optimizer.cpp

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

/*XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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XX                                                                           XX
XX                              Optimizer                                    XX
XX                                                                           XX
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*/

#include "jitpch.h"
#ifdef _MSC_VER
#pragma hdrstop
#endif

/*****************************************************************************/

void Compiler::optInit()
{
    fgHasLoops = false;

    optLoopsRequirePreHeaders = false;
    optNumNaturalLoopsFound   = 0;

#ifdef DEBUG
    loopAlignCandidates = 0;
    loopsAligned        = 0;
#endif

    /* Keep track of the number of calls and indirect calls made by this method */
    optCallCount         = 0;
    optIndirectCallCount = 0;
    optNativeCallCount   = 0;
    optAssertionCount    = 0;
    optAssertionDep      = nullptr;
    optCSEstart          = BAD_VAR_NUM;
    optCSEcount          = 0;
    optCSECandidateCount = 0;
    optCSEattempt        = 0;
    optCSEheuristic      = nullptr;
}

DataFlow::DataFlow(Compiler* pCompiler) : m_pCompiler(pCompiler)
{
}

//------------------------------------------------------------------------
// optSetBlockWeights: adjust block weights, as follows:
// 1. A block that is not reachable from the entry block is marked "run rarely".
// 2. If we're not using profile weights, then any block with a non-zero weight
//    that doesn't dominate all the return blocks has its weight dropped in half
//    (but only if the first block *does* dominate all the returns).
//
// Returns:
//    Suitable phase status
//
// Notes:
//    Depends on dominators, and fgReturnBlocks being set.
//
PhaseStatus Compiler::optSetBlockWeights()
{
    noway_assert(opts.OptimizationEnabled());
    assert(m_domTree != nullptr);
    assert(fgReturnBlocksComputed);

    bool       madeChanges                = false;
    bool       firstBBDominatesAllReturns = true;
    const bool usingProfileWeights        = fgIsUsingProfileWeights();

    // TODO-Quirk: Previously, this code ran on a dominator tree based only on
    // regular flow. This meant that all handlers were not considered to be
    // dominated by fgFirstBB. When those handlers could reach a return
    // block that return was also not considered to be dominated by fgFirstBB.
    // In practice the code below would then not make any changes for those
    // functions. We emulate that behavior here.
    for (EHblkDsc* eh : EHClauses(this))
    {
        BasicBlock* flowBlock = eh->ExFlowBlock();

        for (BasicBlockList* retBlocks = fgReturnBlocks; retBlocks != nullptr; retBlocks = retBlocks->next)
        {
            if (m_dfsTree->Contains(flowBlock) && m_reachabilitySets->CanReach(flowBlock, retBlocks->block))
            {
                firstBBDominatesAllReturns = false;
                break;
            }
        }

        if (!firstBBDominatesAllReturns)
        {
            break;
        }
    }

    for (BasicBlock* const block : Blocks())
    {
        // Blocks that can't be reached via the first block are rarely executed
        if (!m_reachabilitySets->CanReach(fgFirstBB, block) && !block->isRunRarely())
        {
            madeChanges = true;
            block->bbSetRunRarely();
        }

        if (!usingProfileWeights && firstBBDominatesAllReturns)
        {
            // If the weight is already zero (and thus rarely run), there's no point scaling it.
            if (block->bbWeight != BB_ZERO_WEIGHT)
            {
                // If the block dominates all return blocks, leave the weight alone. Otherwise,
                // scale the weight by 0.5 as a heuristic that some other path gets some of the dynamic flow.
                // Note that `optScaleLoopBlocks` has a similar heuristic for loop blocks that don't dominate
                // their loop back edge.

                bool blockDominatesAllReturns = true; // Assume that we will dominate

                for (BasicBlockList* retBlocks = fgReturnBlocks; retBlocks != nullptr; retBlocks = retBlocks->next)
                {
                    // TODO-Quirk: Returns that are unreachable can just be ignored.
                    if (!m_dfsTree->Contains(retBlocks->block) || !m_domTree->Dominates(block, retBlocks->block))
                    {
                        blockDominatesAllReturns = false;
                        break;
                    }
                }

                if (block == fgFirstBB)
                {
                    firstBBDominatesAllReturns = blockDominatesAllReturns;

                    // Don't scale the weight of the first block, since it is guaranteed to execute.
                    // If the first block does not dominate all the returns, we won't scale any of the function's
                    // block weights.
                }
                else
                {
                    // If we are not using profile weight then we lower the weight
                    // of blocks that do not dominate a return block
                    //
                    if (!blockDominatesAllReturns)
                    {
                        madeChanges = true;

                        // TODO-Cleanup: we should use:
                        //    block->scaleBBWeight(0.5);
                        // since we are inheriting "from ourselves", but that leads to asm diffs due to minutely
                        // different floating-point value in the calculation, and some code that compares weights
                        // for equality.
                        block->inheritWeightPercentage(block, 50);
                    }
                }
            }
        }
    }

    return madeChanges ? PhaseStatus::MODIFIED_EVERYTHING : PhaseStatus::MODIFIED_NOTHING;
}

//------------------------------------------------------------------------
// optScaleLoopBlocks: Scale the weight of loop blocks from 'begBlk' to 'endBlk'.
//
// Arguments:
//      begBlk - first block of range. Must be marked as a loop head (BBF_LOOP_HEAD).
//      endBlk - last block of range (inclusive). Must be reachable from `begBlk`.
//
// Operation:
//      Calculate the 'loop weight'. This is the amount to scale the weight of each block in the loop.
//      Our heuristic is that loops are weighted eight times more than straight-line code
//      (scale factor is BB_LOOP_WEIGHT_SCALE). If the loops are all properly formed this gives us these weights:
//
//          1 -- non-loop basic block
//          8 -- single loop nesting
//         64 -- double loop nesting
//        512 -- triple loop nesting
//
void Compiler::optScaleLoopBlocks(BasicBlock* begBlk, BasicBlock* endBlk)
{
    noway_assert(begBlk->bbNum <= endBlk->bbNum);
    noway_assert(begBlk->isLoopHead());
    noway_assert(m_reachabilitySets->CanReach(begBlk, endBlk));
    noway_assert(!opts.MinOpts());

#ifdef DEBUG
    if (verbose)
    {
        printf("\nMarking a loop from " FMT_BB " to " FMT_BB, begBlk->bbNum, endBlk->bbNum);
    }
#endif

    // Build list of back edges for block begBlk.
    FlowEdge* backedgeList = nullptr;

    for (BasicBlock* const predBlock : begBlk->PredBlocks())
    {
        // Is this a back edge?
        if (predBlock->bbNum >= begBlk->bbNum)
        {
            backedgeList = new (this, CMK_FlowEdge) FlowEdge(predBlock, backedgeList);

#if MEASURE_BLOCK_SIZE
            genFlowNodeCnt += 1;
            genFlowNodeSize += sizeof(FlowEdge);
#endif // MEASURE_BLOCK_SIZE
        }
    }

    // At least one backedge must have been found (the one from endBlk).
    noway_assert(backedgeList);

    auto reportBlockWeight = [&](BasicBlock* blk, const char* message) {
#ifdef DEBUG
        if (verbose)
        {
            printf("\n    " FMT_BB "(wt=" FMT_WT ")%s", blk->bbNum, blk->getBBWeight(this), message);
        }
#endif // DEBUG
    };

    for (BasicBlock* const curBlk : BasicBlockRangeList(begBlk, endBlk))
    {
        // Don't change the block weight if it came from profile data.
        if (curBlk->hasProfileWeight() && fgHaveProfileData())
        {
            reportBlockWeight(curBlk, "; unchanged: has profile weight");
            continue;
        }

        // Don't change the block weight if it's known to be rarely run.
        if (curBlk->isRunRarely())
        {
            reportBlockWeight(curBlk, "; unchanged: run rarely");
            continue;
        }

        // For curBlk to be part of a loop that starts at begBlk, curBlk must be reachable from begBlk and
        // (since this is a loop) begBlk must likewise be reachable from curBlk.

        if (m_reachabilitySets->CanReach(curBlk, begBlk) && m_reachabilitySets->CanReach(begBlk, curBlk))
        {
            // If `curBlk` reaches any of the back edge blocks we set `reachable`.
            // If `curBlk` dominates any of the back edge blocks we set `dominates`.
            bool reachable = false;
            bool dominates = false;

            for (FlowEdge* tmp = backedgeList; tmp != nullptr; tmp = tmp->getNextPredEdge())
            {
                BasicBlock* backedge = tmp->getSourceBlock();

                reachable |= m_reachabilitySets->CanReach(curBlk, backedge);
                dominates |= m_domTree->Dominates(curBlk, backedge);

                if (dominates && reachable)
                {
                    // No need to keep looking; we've already found all the info we need.
                    break;
                }
            }

            if (reachable)
            {
                // If the block has BB_ZERO_WEIGHT, then it should be marked as rarely run, and skipped, above.
                noway_assert(curBlk->bbWeight > BB_ZERO_WEIGHT);

                weight_t scale = BB_LOOP_WEIGHT_SCALE;

                if (!dominates)
                {
                    // If `curBlk` reaches but doesn't dominate any back edge to `endBlk` then there must be at least
                    // some other path to `endBlk`, so don't give `curBlk` all the execution weight.
                    scale = scale / 2;
                }

                curBlk->scaleBBWeight(scale);

                reportBlockWeight(curBlk, "");
            }
            else
            {
                reportBlockWeight(curBlk, "; unchanged: back edge unreachable");
            }
        }
        else
        {
            reportBlockWeight(curBlk, "; unchanged: block not in loop");
        }
    }
}

//----------------------------------------------------------------------------------
// optIsLoopIncrTree: Check if loop is a tree of form v = v op const.
//
// Arguments:
//      incr - The incr tree to be checked.
//
//  Return Value:
//      iterVar local num if the iterVar is found, otherwise BAD_VAR_NUM.
//
unsigned Compiler::optIsLoopIncrTree(GenTree* incr)
{
    GenTree*   incrVal;
    genTreeOps updateOper;
    unsigned   iterVar = incr->IsLclVarUpdateTree(&incrVal, &updateOper);
    if (iterVar != BAD_VAR_NUM)
    {
        // We have v = v op y type node.
        switch (updateOper)
        {
            case GT_ADD:
            case GT_SUB:
            case GT_MUL:
            case GT_RSH:
            case GT_LSH:
                break;
            default:
                return BAD_VAR_NUM;
        }

        // Increment should be by a const int.
        // TODO-CQ: CLONE: allow variable increments.
        if ((incrVal->gtOper != GT_CNS_INT) || (incrVal->TypeGet() != TYP_INT))
        {
            return BAD_VAR_NUM;
        }
    }

    return iterVar;
}

//----------------------------------------------------------------------------------
// optIsLoopTestEvalIntoTemp:
//      Pattern match if the test tree is computed into a tmp
//      and the "tmp" is used as jump condition for loop termination.
//
// Arguments:
//      testStmt    - is the JTRUE statement that is of the form: jmpTrue (Vtmp != 0)
//                    where Vtmp contains the actual loop test result.
//      newTestStmt - contains the statement that is the actual test stmt involving
//                    the loop iterator.
//
//  Return Value:
//      Returns true if a new test tree can be obtained.
//
//  Operation:
//      Scan if the current stmt is a jtrue with (Vtmp != 0) as condition
//      Then returns the rhs for def of Vtmp as the "test" node.
//
//  Note:
//      This method just retrieves what it thinks is the "test" node,
//      the callers are expected to verify that "iterVar" is used in the test.
//
bool Compiler::optIsLoopTestEvalIntoTemp(Statement* testStmt, Statement** newTestStmt)
{
    GenTree* test = testStmt->GetRootNode();

    if (test->gtOper != GT_JTRUE)
    {
        return false;
    }

    GenTree* relop = test->gtGetOp1();
    noway_assert(relop->OperIsCompare());

    GenTree* opr1 = relop->AsOp()->gtOp1;
    GenTree* opr2 = relop->AsOp()->gtOp2;

    // Make sure we have jtrue (vtmp != 0)
    if ((relop->OperGet() == GT_NE) && (opr1->OperGet() == GT_LCL_VAR) && (opr2->OperGet() == GT_CNS_INT) &&
        opr2->IsIntegralConst(0))
    {
        // Get the previous statement to get the def (rhs) of Vtmp to see
        // if the "test" is evaluated into Vtmp.
        Statement* prevStmt = testStmt->GetPrevStmt();
        if (prevStmt == nullptr)
        {
            return false;
        }

        GenTree* tree = prevStmt->GetRootNode();
        if (tree->OperIs(GT_STORE_LCL_VAR) && (tree->AsLclVar()->GetLclNum() == opr1->AsLclVar()->GetLclNum()) &&
            tree->AsLclVar()->Data()->OperIsCompare())
        {
            *newTestStmt = prevStmt;
            return true;
        }
    }
    return false;
}

//----------------------------------------------------------------------------------
// optExtractInitTestIncr:
//      Extract the "init", "test" and "incr" nodes of the loop.
//
// Arguments:
//      pInitBlock - [IN/OUT] *pInitBlock is the loop head block on entry, and is set to the initBlock on exit,
//                   if `**ppInit` is non-null.
//      cond       - A BBJ_COND block that exits the loop
//      header     - Loop header block
//      ppInit     - [out] The init stmt of the loop if found.
//      ppTest     - [out] The test stmt of the loop if found.
//      ppIncr     - [out] The incr stmt of the loop if found.
//
//  Return Value:
//      The results are put in "ppInit", "ppTest" and "ppIncr" if the method
//      returns true. Returns false if the information can't be extracted.
//      Extracting the `init` is optional; if one is not found, *ppInit is set
//      to nullptr. Return value will never be false if `init` is not found.
//
//  Operation:
//      Check if the "test" stmt is last stmt in an exiting BBJ_COND block of the loop. Try to find the "incr" stmt.
//      Check previous stmt of "test" to get the "incr" stmt.
//
//  Note:
//      This method just retrieves what it thinks is the "test" node,
//      the callers are expected to verify that "iterVar" is used in the test.
//
bool Compiler::optExtractInitTestIncr(
    BasicBlock** pInitBlock, BasicBlock* cond, BasicBlock* header, GenTree** ppInit, GenTree** ppTest, GenTree** ppIncr)
{
    assert(pInitBlock != nullptr);
    assert(ppInit != nullptr);
    assert(ppTest != nullptr);
    assert(ppIncr != nullptr);

    // Check if last two statements in the loop body are the increment of the iterator
    // and the loop termination test.
    noway_assert(cond->bbStmtList != nullptr);
    Statement* testStmt = cond->lastStmt();
    noway_assert(testStmt != nullptr && testStmt->GetNextStmt() == nullptr);

    Statement* newTestStmt;
    if (optIsLoopTestEvalIntoTemp(testStmt, &newTestStmt))
    {
        testStmt = newTestStmt;
    }

    // Check if we have the incr stmt before the test stmt, if we don't,
    // check if incr is part of the loop "header".
    Statement* incrStmt = testStmt->GetPrevStmt();

    // If we've added profile instrumentation, we may need to skip past a BB counter update.
    //
    if (opts.jitFlags->IsSet(JitFlags::JIT_FLAG_BBINSTR) && (incrStmt != nullptr) &&
        incrStmt->GetRootNode()->IsBlockProfileUpdate())
    {
        incrStmt = incrStmt->GetPrevStmt();
    }

    if (incrStmt == nullptr || (optIsLoopIncrTree(incrStmt->GetRootNode()) == BAD_VAR_NUM))
    {
        return false;
    }

    assert(testStmt != incrStmt);

    // Find the last statement in the loop pre-header which we expect to be the initialization of
    // the loop iterator.
    BasicBlock* initBlock = *pInitBlock;
    Statement*  phdrStmt  = initBlock->firstStmt();
    if (phdrStmt == nullptr)
    {
        // When we build the loops, we canonicalize by introducing loop pre-headers for all loops.
        // If we are rebuilding the loops, we would already have the pre-header block introduced
        // the first time, which might be empty if no hoisting has yet occurred. In this case, look a
        // little harder for the possible loop initialization statement.
        if (initBlock->KindIs(BBJ_ALWAYS) && initBlock->TargetIs(header))
        {
            BasicBlock* uniquePred = initBlock->GetUniquePred(this);
            if (uniquePred != nullptr)
            {
                initBlock = uniquePred;
                phdrStmt  = initBlock->firstStmt();
            }
        }
    }

    if (phdrStmt != nullptr)
    {
        Statement* initStmt = phdrStmt->GetPrevStmt();
        noway_assert(initStmt != nullptr && (initStmt->GetNextStmt() == nullptr));

        // If it is a duplicated loop condition, skip it.
        if (initStmt->GetRootNode()->OperIs(GT_JTRUE))
        {
            bool doGetPrev = true;
#ifdef DEBUG
            if (opts.optRepeat)
            {
                // Previous optimization passes may have inserted compiler-generated
                // statements other than duplicated loop conditions.
                doGetPrev = (initStmt->GetPrevStmt() != nullptr);
            }
#endif // DEBUG
            if (doGetPrev)
            {
                initStmt = initStmt->GetPrevStmt();
            }
            noway_assert(initStmt != nullptr);
        }

        *ppInit     = initStmt->GetRootNode();
        *pInitBlock = initBlock;
    }
    else
    {
        *ppInit = nullptr;
    }

    *ppTest = testStmt->GetRootNode();
    *ppIncr = incrStmt->GetRootNode();

    return true;
}

#ifdef DEBUG
void Compiler::optCheckPreds()
{
    for (BasicBlock* const block : Blocks())
    {
        for (BasicBlock* const predBlock : block->PredBlocks())
        {
            // make sure this pred is part of the BB list
            BasicBlock* bb;
            for (bb = fgFirstBB; bb; bb = bb->Next())
            {
                if (bb == predBlock)
                {
                    break;
                }
            }
            noway_assert(bb);
            switch (bb->GetKind())
            {
                case BBJ_COND:
                    if (bb->TrueTargetIs(block))
                    {
                        break;
                    }
                    noway_assert(bb->FalseTargetIs(block));
                    break;
                case BBJ_EHFILTERRET:
                case BBJ_ALWAYS:
                case BBJ_EHCATCHRET:
                    noway_assert(bb->TargetIs(block));
                    break;
                default:
                    break;
            }
        }
    }
}

#endif // DEBUG

//------------------------------------------------------------------------
// optRedirectBlock: Replace the branch successors of a block based on a block map.
//
// Updates the successors of `blk`: if `blk2` is a branch successor of `blk`, and there is a mapping
// for `blk2->blk3` in `redirectMap`, change `blk` so that `blk3` is this branch successor.
//
// Arguments:
//     blk          - block to redirect
//     redirectMap  - block->block map specifying how the `blk` target will be redirected.
//     predOption   - specifies how to update the pred lists
//
// Notes:
//     Pred lists for successors of `blk` may be changed, depending on `predOption`.
//
void Compiler::optRedirectBlock(BasicBlock* blk, BlockToBlockMap* redirectMap, RedirectBlockOption predOption)
{
    const bool updatePreds = (predOption == RedirectBlockOption::UpdatePredLists);
    const bool addPreds    = (predOption == RedirectBlockOption::AddToPredLists);

    BasicBlock* newJumpDest = nullptr;

    switch (blk->GetKind())
    {
        case BBJ_THROW:
        case BBJ_RETURN:
        case BBJ_EHFILTERRET:
        case BBJ_EHFAULTRET:
        case BBJ_EHCATCHRET:
            // These have no jump destination to update.
            break;

        case BBJ_CALLFINALLY:
            if (addPreds && blk->bbFallsThrough())
            {
                fgAddRefPred(blk->Next(), blk);
            }

            FALLTHROUGH;
        case BBJ_ALWAYS:
        case BBJ_LEAVE:
        case BBJ_CALLFINALLYRET:
            // All of these have a single jump destination to update.
            if (redirectMap->Lookup(blk->GetTarget(), &newJumpDest))
            {
                if (updatePreds)
                {
                    fgRemoveRefPred(blk->GetTarget(), blk);
                }
                blk->SetTarget(newJumpDest);
                if (updatePreds || addPreds)
                {
                    fgAddRefPred(newJumpDest, blk);
                }
            }
            else if (addPreds)
            {
                fgAddRefPred(blk->GetTarget(), blk);
            }
            break;

        case BBJ_COND:
            // Update jump taken when condition is true
            if (redirectMap->Lookup(blk->GetTrueTarget(), &newJumpDest))
            {
                if (updatePreds)
                {
                    fgRemoveRefPred(blk->GetTrueTarget(), blk);
                }
                blk->SetTrueTarget(newJumpDest);
                if (updatePreds || addPreds)
                {
                    fgAddRefPred(newJumpDest, blk);
                }
            }
            else if (addPreds)
            {
                fgAddRefPred(blk->GetTrueTarget(), blk);
            }

            // Update jump taken when condition is false
            if (redirectMap->Lookup(blk->GetFalseTarget(), &newJumpDest))
            {
                if (updatePreds)
                {
                    fgRemoveRefPred(blk->GetFalseTarget(), blk);
                }
                blk->SetFalseTarget(newJumpDest);
                if (updatePreds || addPreds)
                {
                    fgAddRefPred(newJumpDest, blk);
                }
            }
            else if (addPreds)
            {
                fgAddRefPred(blk->GetFalseTarget(), blk);
            }
            break;

        case BBJ_EHFINALLYRET:
        {
            BBehfDesc*  ehfDesc = blk->GetEhfTargets();
            BasicBlock* newSucc = nullptr;
            for (unsigned i = 0; i < ehfDesc->bbeCount; i++)
            {
                BasicBlock* const succ = ehfDesc->bbeSuccs[i];
                if (redirectMap->Lookup(succ, &newSucc))
                {
                    if (updatePreds)
                    {
                        fgRemoveRefPred(succ, blk);
                    }
                    if (updatePreds || addPreds)
                    {
                        fgAddRefPred(newSucc, blk);
                    }
                    ehfDesc->bbeSuccs[i] = newSucc;
                }
                else if (addPreds)
                {
                    fgAddRefPred(succ, blk);
                }
            }
        }
        break;

        case BBJ_SWITCH:
        {
            bool redirected = false;
            for (unsigned i = 0; i < blk->GetSwitchTargets()->bbsCount; i++)
            {
                BasicBlock* const switchDest = blk->GetSwitchTargets()->bbsDstTab[i];
                if (redirectMap->Lookup(switchDest, &newJumpDest))
                {
                    if (updatePreds)
                    {
                        fgRemoveRefPred(switchDest, blk);
                    }
                    if (updatePreds || addPreds)
                    {
                        fgAddRefPred(newJumpDest, blk);
                    }
                    blk->GetSwitchTargets()->bbsDstTab[i] = newJumpDest;
                    redirected                            = true;
                }
                else if (addPreds)
                {
                    fgAddRefPred(switchDest, blk);
                }
            }
            // If any redirections happened, invalidate the switch table map for the switch.
            if (redirected)
            {
                // Don't create a new map just to try to remove an entry.
                BlockToSwitchDescMap* switchMap = GetSwitchDescMap(/* createIfNull */ false);
                if (switchMap != nullptr)
                {
                    switchMap->Remove(blk);
                }
            }
        }
        break;

        default:
            unreached();
    }
}

//-----------------------------------------------------------------------------
// optIterSmallOverflow: Helper for loop unrolling. Determine if "i += const" will
// cause an overflow exception for the small types.
//
// Arguments:
//    iterAtExit - iteration constant at loop exit
//    incrType   - type of increment
//
// Returns:
//   true if overflow
//
// static
bool Compiler::optIterSmallOverflow(int iterAtExit, var_types incrType)
{
    int type_MAX;

    switch (incrType)
    {
        case TYP_BYTE:
            type_MAX = SCHAR_MAX;
            break;
        case TYP_UBYTE:
            type_MAX = UCHAR_MAX;
            break;
        case TYP_SHORT:
            type_MAX = SHRT_MAX;
            break;
        case TYP_USHORT:
            type_MAX = USHRT_MAX;
            break;

        case TYP_UINT: // Detected by checking for 32bit ....
        case TYP_INT:
            return false; // ... overflow same as done for TYP_INT

        default:
            NO_WAY("Bad type");
    }

    if (iterAtExit > type_MAX)
    {
        return true;
    }
    else
    {
        return false;
    }
}

//-----------------------------------------------------------------------------
// optIterSmallUnderflow: Helper for loop unrolling. Determine if "i -= const" will
// cause an underflow exception for the small types.
//
// Arguments:
//    iterAtExit - iteration constant at loop exit
//    decrType   - type of decrement
//
// Returns:
//   true if overflow
//
// static
bool Compiler::optIterSmallUnderflow(int iterAtExit, var_types decrType)
{
    int type_MIN;

    switch (decrType)
    {
        case TYP_BYTE:
            type_MIN = SCHAR_MIN;
            break;
        case TYP_SHORT:
            type_MIN = SHRT_MIN;
            break;
        case TYP_UBYTE:
            type_MIN = 0;
            break;
        case TYP_USHORT:
            type_MIN = 0;
            break;

        case TYP_UINT: // Detected by checking for 32bit ....
        case TYP_INT:
            return false; // ... underflow same as done for TYP_INT

        default:
            NO_WAY("Bad type");
    }

    if (iterAtExit < type_MIN)
    {
        return true;
    }
    else
    {
        return false;
    }
}

//-----------------------------------------------------------------------------
// optComputeLoopRep: Helper for loop unrolling. Computes the number of times
// the test block of a loop is executed.
//
// Arguments:
//    constInit     - loop constant initial value
//    constLimit    - loop constant limit
//    iterInc       - loop iteration increment
//    iterOper      - loop iteration increment operator (ADD, SUB, etc.)
//    iterOperType  - iteration operator type
//    testOper      - type of loop test (i.e. GT_LE, GT_GE, etc.)
//    unsTest       - true if test is unsigned
//    iterCount     - *iterCount is set to the iteration count, if the function returns `true`
//
// Returns:
//   true if the loop has a constant repetition count, false if that cannot be proven
//
bool Compiler::optComputeLoopRep(int        constInit,
                                 int        constLimit,
                                 int        iterInc,
                                 genTreeOps iterOper,
                                 var_types  iterOperType,
                                 genTreeOps testOper,
                                 bool       unsTest,
                                 unsigned*  iterCount)
{
    noway_assert(genActualType(iterOperType) == TYP_INT);

    __int64 constInitX;
    __int64 constLimitX;

    unsigned loopCount;
    int      iterSign;

    // Using this, we can just do a signed comparison with other 32 bit values.
    if (unsTest)
    {
        constLimitX = (unsigned int)constLimit;
    }
    else
    {
        constLimitX = (signed int)constLimit;
    }

    switch (iterOperType)
    {
// For small types, the iteration operator will narrow these values if big

#define INIT_ITER_BY_TYPE(type)                                                                                        \
    constInitX = (type)constInit;                                                                                      \
    iterInc    = (type)iterInc;

        case TYP_BYTE:
            INIT_ITER_BY_TYPE(signed char);
            break;
        case TYP_UBYTE:
            INIT_ITER_BY_TYPE(unsigned char);
            break;
        case TYP_SHORT:
            INIT_ITER_BY_TYPE(signed short);
            break;
        case TYP_USHORT:
            INIT_ITER_BY_TYPE(unsigned short);
            break;

        // For the big types, 32 bit arithmetic is performed

        case TYP_INT:
            if (unsTest)
            {
                constInitX = (unsigned int)constInit;
            }
            else
            {
                constInitX = (signed int)constInit;
            }
            break;

        default:
            noway_assert(!"Bad type");
            NO_WAY("Bad type");
    }

    // If iterInc is zero we have an infinite loop.
    if (iterInc == 0)
    {
        return false;
    }

    iterSign  = (iterInc > 0) ? +1 : -1;
    loopCount = 0;

    // bail if count is based on wrap-around math
    if (iterInc > 0)
    {
        if (constLimitX < constInitX)
        {
            return false;
        }
    }
    else if (constLimitX > constInitX)
    {
        return false;
    }

    // Compute the number of repetitions.

    switch (testOper)
    {
        __int64 iterAtExitX;

        case GT_EQ:
            // Something like "for (i=init; i == lim; i++)" doesn't make any sense.
            return false;

        case GT_NE:
            // Consider: "for (i = init; i != lim; i += const)"
            // This is tricky since it may have a constant number of iterations or loop forever.
            // We have to compute "(lim - init) mod iterInc" to see if it is zero.
            // If "mod iterInc" is not zero then the limit test will miss and a wrap will occur
            // which is probably not what the end user wanted, but it is legal.

            if (iterInc > 0)
            {
                // Stepping by one, i.e. Mod with 1 is always zero.
                if (iterInc != 1)
                {
                    if (((constLimitX - constInitX) % iterInc) != 0)
                    {
                        return false;
                    }
                }
            }
            else
            {
                // Stepping by -1, i.e. Mod with 1 is always zero.
                if (iterInc != -1)
                {
                    if (((constInitX - constLimitX) % (-iterInc)) != 0)
                    {
                        return false;
                    }
                }
            }

            switch (iterOper)
            {
                case GT_SUB:
                    iterInc = -iterInc;
                    FALLTHROUGH;

                case GT_ADD:
                    if (constInitX != constLimitX)
                    {
                        loopCount += (unsigned)((constLimitX - constInitX - iterSign) / iterInc) + 1;
                    }

                    iterAtExitX = (int)(constInitX + iterInc * (int)loopCount);

                    if (unsTest)
                    {
                        iterAtExitX = (unsigned)iterAtExitX;
                    }

                    // Check if iteration incr will cause overflow for small types
                    if (optIterSmallOverflow((int)iterAtExitX, iterOperType))
                    {
                        return false;
                    }

                    // iterator with 32bit overflow. Bad for TYP_(U)INT
                    if (iterAtExitX < constLimitX)
                    {
                        return false;
                    }

                    *iterCount = loopCount;
                    return true;

                case GT_MUL:
                case GT_DIV:
                case GT_RSH:
                case GT_LSH:
                case GT_UDIV:
                    return false;

                default:
                    noway_assert(!"Unknown operator for loop iterator");
                    return false;
            }

        case GT_LT:
            switch (iterOper)
            {
                case GT_SUB:
                    iterInc = -iterInc;
                    FALLTHROUGH;

                case GT_ADD:
                    if (constInitX < constLimitX)
                    {
                        loopCount += (unsigned)((constLimitX - constInitX - iterSign) / iterInc) + 1;
                    }

                    iterAtExitX = (int)(constInitX + iterInc * (int)loopCount);

                    if (unsTest)
                    {
                        iterAtExitX = (unsigned)iterAtExitX;
                    }

                    // Check if iteration incr will cause overflow for small types
                    if (optIterSmallOverflow((int)iterAtExitX, iterOperType))
                    {
                        return false;
                    }

                    // iterator with 32bit overflow. Bad for TYP_(U)INT
                    if (iterAtExitX < constLimitX)
                    {
                        return false;
                    }

                    *iterCount = loopCount;
                    return true;

                case GT_MUL:
                case GT_DIV:
                case GT_RSH:
                case GT_LSH:
                case GT_UDIV:
                    return false;

                default:
                    noway_assert(!"Unknown operator for loop iterator");
                    return false;
            }

        case GT_LE:
            switch (iterOper)
            {
                case GT_SUB:
                    iterInc = -iterInc;
                    FALLTHROUGH;

                case GT_ADD:
                    if (constInitX <= constLimitX)
                    {
                        loopCount += (unsigned)((constLimitX - constInitX) / iterInc) + 1;
                    }

                    iterAtExitX = (int)(constInitX + iterInc * (int)loopCount);

                    if (unsTest)
                    {
                        iterAtExitX = (unsigned)iterAtExitX;
                    }

                    // Check if iteration incr will cause overflow for small types
                    if (optIterSmallOverflow((int)iterAtExitX, iterOperType))
                    {
                        return false;
                    }

                    // iterator with 32bit overflow. Bad for TYP_(U)INT
                    if (iterAtExitX <= constLimitX)
                    {
                        return false;
                    }

                    *iterCount = loopCount;
                    return true;

                case GT_MUL:
                case GT_DIV:
                case GT_RSH:
                case GT_LSH:
                case GT_UDIV:
                    return false;

                default:
                    noway_assert(!"Unknown operator for loop iterator");
                    return false;
            }

        case GT_GT:
            switch (iterOper)
            {
                case GT_SUB:
                    iterInc = -iterInc;
                    FALLTHROUGH;

                case GT_ADD:
                    if (constInitX > constLimitX)
                    {
                        loopCount += (unsigned)((constLimitX - constInitX - iterSign) / iterInc) + 1;
                    }

                    iterAtExitX = (int)(constInitX + iterInc * (int)loopCount);

                    if (unsTest)
                    {
                        iterAtExitX = (unsigned)iterAtExitX;
                    }

                    // Check if small types will underflow
                    if (optIterSmallUnderflow((int)iterAtExitX, iterOperType))
                    {
                        return false;
                    }

                    // iterator with 32bit underflow. Bad for TYP_INT and unsigneds
                    if (iterAtExitX > constLimitX)
                    {
                        return false;
                    }

                    *iterCount = loopCount;
                    return true;

                case GT_MUL:
                case GT_DIV:
                case GT_RSH:
                case GT_LSH:
                case GT_UDIV:
                    return false;

                default:
                    noway_assert(!"Unknown operator for loop iterator");
                    return false;
            }

        case GT_GE:
            switch (iterOper)
            {
                case GT_SUB:
                    iterInc = -iterInc;
                    FALLTHROUGH;

                case GT_ADD:
                    if (constInitX >= constLimitX)
                    {
                        loopCount += (unsigned)((constLimitX - constInitX) / iterInc) + 1;
                    }

                    iterAtExitX = (int)(constInitX + iterInc * (int)loopCount);

                    if (unsTest)
                    {
                        iterAtExitX = (unsigned)iterAtExitX;
                    }

                    // Check if small types will underflow
                    if (optIterSmallUnderflow((int)iterAtExitX, iterOperType))
                    {
                        return false;
                    }

                    // iterator with 32bit underflow. Bad for TYP_INT and unsigneds
                    if (iterAtExitX >= constLimitX)
                    {
                        return false;
                    }

                    *iterCount = loopCount;
                    return true;

                case GT_MUL:
                case GT_DIV:
                case GT_RSH:
                case GT_LSH:
                case GT_UDIV:
                    return false;

                default:
                    noway_assert(!"Unknown operator for loop iterator");
                    return false;
            }

        default:
            noway_assert(!"Unknown operator for loop condition");
    }

    return false;
}

//-----------------------------------------------------------------------------
// optUnrollLoops: Look for loop unrolling candidates and unroll them.
//
// Loops must be of the form:
//   for (i=icon; i<icon; i++) { ... }
//
// Loops handled are fully unrolled; there is no partial unrolling.
//
// Limitations: only the following loop types are handled:
// 1. constant initializer, constant bound
// 2. The entire loop must be in the same EH region.
// 3. The loop iteration variable can't be address exposed.
// 4. The loop iteration variable can't be a promoted struct field.
// 5. We must be able to calculate the total constant iteration count.
//
// Cost heuristics:
// 1. there are cost metrics for maximum number of allowed iterations, and maximum unroll size
// 2. constant trip count loops are always allowed, up to a limit of 4
// 3. otherwise, only loops where the limit is Vector<T>.Length are currently allowed
//
// In stress modes, these heuristic limits are expanded, and loops aren't required to have the
// Vector<T>.Length limit.
//
// Loops are processed from innermost to outermost order, to attempt to unroll the most nested loops first.
//
// Returns:
//   suitable phase status
//
PhaseStatus Compiler::optUnrollLoops()
{
    if (compCodeOpt() == SMALL_CODE)
    {
        return PhaseStatus::MODIFIED_NOTHING;
    }

    if (m_loops->NumLoops() == 0)
    {
        return PhaseStatus::MODIFIED_NOTHING;
    }

#ifdef DEBUG
    if (JitConfig.JitNoUnroll())
    {
        return PhaseStatus::MODIFIED_NOTHING;
    }
#endif

    // Look for loop unrolling candidates

    int  unrollCount = 0;
    bool anyIRchange = false;

    int passes = 0;

    while (true)
    {
        // We track loops for which we unrolled a descendant loop. Since unrolling
        // introduces/removes blocks, we retry unrolling for the parent loops
        // separately, to avoid having to maintain the removed/added blocks.
        BitVecTraits loopTraits((unsigned)m_loops->NumLoops(), this);
        BitVec       loopsWithUnrolledDescendant(BitVecOps::MakeEmpty(&loopTraits));

        // Visit loops in post order (inner loops before outer loops).
        for (FlowGraphNaturalLoop* loop : m_loops->InPostOrder())
        {
            if (BitVecOps::IsMember(&loopTraits, loopsWithUnrolledDescendant, loop->GetIndex()))
            {
                continue;
            }

            if (!optTryUnrollLoop(loop, &anyIRchange))
            {
                continue;
            }

            unrollCount++;

            // Mark in all ancestors now that one of their descendant loops was
            // unrolled to indicate that the set of loop blocks changed.
            for (FlowGraphNaturalLoop* ancestor = loop->GetParent(); ancestor != nullptr;
                 ancestor                       = ancestor->GetParent())
            {
                BitVecOps::AddElemD(&loopTraits, loopsWithUnrolledDescendant, ancestor->GetIndex());
            }
        }

        if ((unrollCount == 0) || BitVecOps::IsEmpty(&loopTraits, loopsWithUnrolledDescendant) || (passes >= 10))
        {
            break;
        }

        JITDUMP("A nested loop was unrolled. Doing another pass (pass %d)\n", passes + 1);
        fgRenumberBlocks();
        fgInvalidateDfsTree();
        m_dfsTree = fgComputeDfs();
        m_loops   = FlowGraphNaturalLoops::Find(m_dfsTree);
        passes++;
    }

    if (unrollCount > 0)
    {
        assert(anyIRchange);

#ifdef DEBUG
        if (verbose)
        {
            printf("\nFinished unrolling %d loops in %d passes", unrollCount, passes);
            printf("\n");
        }
#endif // DEBUG

        // We left the old loops unreachable as part of unrolling, so get rid of
        // those blocks now.
        fgDfsBlocksAndRemove();
        m_loops = FlowGraphNaturalLoops::Find(m_dfsTree);

        fgRenumberBlocks();

        DBEXEC(verbose, fgDispBasicBlocks());
    }

#ifdef DEBUG
    fgDebugCheckBBlist(true);
#endif // DEBUG

    return anyIRchange ? PhaseStatus::MODIFIED_EVERYTHING : PhaseStatus::MODIFIED_NOTHING;
}

//-----------------------------------------------------------------------------
// optTryUnrollLoop: Do legality and profitability checks and try to unroll a
// single loop.
//
// Parameters:
//   loop      - The loop to try unrolling
//   changedIR - [out] Whether or not the IR was changed. Can be true even if
//               the function returns false.
//
// Returns:
//   True if the loop was unrolled, in which case the flow graph was changed.
//
bool Compiler::optTryUnrollLoop(FlowGraphNaturalLoop* loop, bool* changedIR)
{
    static const unsigned ITER_LIMIT[COUNT_OPT_CODE + 1] = {
        10, // BLENDED_CODE
        0,  // SMALL_CODE
        20, // FAST_CODE
        0   // COUNT_OPT_CODE
    };

    assert(ITER_LIMIT[SMALL_CODE] == 0);
    assert(ITER_LIMIT[COUNT_OPT_CODE] == 0);

    unsigned iterLimit = ITER_LIMIT[compCodeOpt()];

#ifdef DEBUG
    if (compStressCompile(STRESS_UNROLL_LOOPS, 50))
    {
        iterLimit *= 10;
    }
#endif

    static const int UNROLL_LIMIT_SZ[COUNT_OPT_CODE + 1] = {
        300, // BLENDED_CODE
        0,   // SMALL_CODE
        600, // FAST_CODE
        0    // COUNT_OPT_CODE
    };

    assert(UNROLL_LIMIT_SZ[SMALL_CODE] == 0);
    assert(UNROLL_LIMIT_SZ[COUNT_OPT_CODE] == 0);

    NaturalLoopIterInfo iterInfo;
    if (!loop->AnalyzeIteration(&iterInfo))
    {
        return false;
    }

    // Check for required flags:
    // HasConstInit  - required because this transform only handles full unrolls
    // HasConstLimit - required because this transform only handles full unrolls
    if (!iterInfo.HasConstInit || !iterInfo.HasConstLimit)
    {
        // Don't print to the JitDump about this common case.
        return false;
    }

    // The loop test must be both an exit and a backedge.
    // FlowGraphNaturalLoop::AnalyzeIteration ensures it is an exit but we must
    // make sure it is a backedge so that we can legally redirect it to the
    // next iteration. If it isn't a backedge then redirecting it would skip
    // all code between the loop test and the backedge.
    assert(loop->ContainsBlock(iterInfo.TestBlock->GetTrueTarget()) !=
           loop->ContainsBlock(iterInfo.TestBlock->GetFalseTarget()));
    if (!iterInfo.TestBlock->TrueTargetIs(loop->GetHeader()) && !iterInfo.TestBlock->FalseTargetIs(loop->GetHeader()))
    {
        JITDUMP("Failed to unroll loop " FMT_LP ": test block is not a backedge\n", loop->GetIndex());
        return false;
    }

    // Get the loop data:
    //  - initial constant
    //  - limit constant
    //  - iterator
    //  - iterator increment
    //  - increment operation type (i.e. ADD, SUB, etc...)
    //  - loop test type (i.e. GT_GE, GT_LT, etc...)

    int        lbeg         = iterInfo.ConstInitValue;
    int        llim         = iterInfo.ConstLimit();
    genTreeOps testOper     = iterInfo.TestOper();
    unsigned   lvar         = iterInfo.IterVar;
    int        iterInc      = iterInfo.IterConst();
    genTreeOps iterOper     = iterInfo.IterOper();
    var_types  iterOperType = iterInfo.IterOperType();
    bool       unsTest      = (iterInfo.TestTree->gtFlags & GTF_UNSIGNED) != 0;

    assert(!lvaGetDesc(lvar)->IsAddressExposed());
    assert(!lvaGetDesc(lvar)->lvIsStructField);

    JITDUMP("Analyzing candidate for loop unrolling:\n");
    DBEXEC(verbose, FlowGraphNaturalLoop::Dump(loop));

    // Find the number of iterations - the function returns false if not a constant number.
    unsigned totalIter;
    if (!optComputeLoopRep(lbeg, llim, iterInc, iterOper, iterOperType, testOper, unsTest, &totalIter))
    {
        JITDUMP("Failed to unroll loop " FMT_LP ": not a constant iteration count\n", loop->GetIndex());
        return false;
    }

    JITDUMP("Computed loop repetition count (number of test block executions) to be %u\n", totalIter);

    // Forget it if there are too many repetitions or not a constant loop.

    if (totalIter > iterLimit)
    {
        JITDUMP("Failed to unroll loop " FMT_LP ": too many iterations (%d > %d) (heuristic)\n", loop->GetIndex(),
                totalIter, iterLimit);
        return false;
    }

    int unrollLimitSz = UNROLL_LIMIT_SZ[compCodeOpt()];

    if (INDEBUG(compStressCompile(STRESS_UNROLL_LOOPS, 50) ||) false)
    {
        // In stress mode, quadruple the size limit, and drop
        // the restriction that loop limit must be vector element count.
        unrollLimitSz *= 4;
    }
    else if (totalIter <= 1)
    {
        // No limit for single iteration loops
        // If there is no iteration (totalIter == 0), we will remove the loop body entirely.
        unrollLimitSz = INT_MAX;
    }
    else if (totalIter <= opts.compJitUnrollLoopMaxIterationCount)
    {
        // We can unroll this
    }
    else if (iterInfo.HasSimdLimit)
    {
        // We can unroll this
    }
    else
    {
        JITDUMP("Failed to unroll loop " FMT_LP ": insufficiently simple loop (heuristic)\n", loop->GetIndex());
        return false;
    }

    GenTree* incr = iterInfo.IterTree;

    // Don't unroll loops we don't understand.
    if (!incr->OperIs(GT_STORE_LCL_VAR))
    {
        JITDUMP("Failed to unroll loop " FMT_LP ": unknown increment op (%s)\n", loop->GetIndex(),
                GenTree::OpName(incr->gtOper));
        return false;
    }
    incr = incr->AsLclVar()->Data();

    // Make sure everything looks ok.
    assert((iterInfo.TestBlock != nullptr) && iterInfo.TestBlock->KindIs(BBJ_COND));

    // clang-format off
    if (!incr->OperIs(GT_ADD, GT_SUB) ||
        !incr->AsOp()->gtOp1->OperIs(GT_LCL_VAR) ||
        (incr->AsOp()->gtOp1->AsLclVarCommon()->GetLclNum() != lvar) ||
        !incr->AsOp()->gtOp2->OperIs(GT_CNS_INT) ||
        (incr->AsOp()->gtOp2->AsIntCon()->gtIconVal != iterInc) ||

        (iterInfo.TestBlock->lastStmt()->GetRootNode()->gtGetOp1() != iterInfo.TestTree))
    {
        noway_assert(!"Bad precondition in Compiler::optUnrollLoops()");
        return false;
    }
    // clang-format on

    INDEBUG(const char* reason);
    if (!loop->CanDuplicate(INDEBUG(&reason)))
    {
        JITDUMP("Failed to unroll loop " FMT_LP ": %s\n", loop->GetIndex(), reason);
        return false;
    }

    // After this point, assume we've changed the IR. In particular, we call
    // gtSetStmtInfo() which can modify the IR.
    *changedIR = true;

    // Heuristic: Estimated cost in code size of the unrolled loop.

    ClrSafeInt<unsigned> loopCostSz; // Cost is size of one iteration

    loop->VisitLoopBlocksReversePostOrder([=, &loopCostSz](BasicBlock* block) {
        for (Statement* const stmt : block->Statements())
        {
            gtSetStmtInfo(stmt);
            loopCostSz += stmt->GetCostSz();
        }

        return BasicBlockVisit::Continue;
    });

#ifdef DEBUG
    // Today we will never see any BBJ_RETURN blocks because we cannot
    // duplicate loops with EH in them. When we have no try-regions that start
    // in the loop it is not possible for BBJ_RETURN blocks to be part of the
    // loop; a BBJ_RETURN block can only be part of the loop if its exceptional
    // flow can reach the header, but that would require the handler to also be
    // part of the loop, which guarantees that the loop contains two distinct
    // EH regions.
    loop->VisitLoopBlocks([](BasicBlock* block) {
        assert(!block->KindIs(BBJ_RETURN));
        return BasicBlockVisit::Continue;
    });
#endif

    // Compute the estimated increase in code size for the unrolled loop.

    ClrSafeInt<unsigned> fixedLoopCostSz(8);

    ClrSafeInt<int> unrollCostSz =
        ClrSafeInt<int>(loopCostSz * ClrSafeInt<unsigned>(totalIter)) - ClrSafeInt<int>(loopCostSz + fixedLoopCostSz);

    // Don't unroll if too much code duplication would result.

    if (unrollCostSz.IsOverflow() || (unrollCostSz.Value() > unrollLimitSz))
    {
        JITDUMP("Failed to unroll loop " FMT_LP ": size constraint (%d > %d) (heuristic)\n", loop->GetIndex(),
                unrollCostSz.Value(), unrollLimitSz);
        return false;
    }

    // Looks like a good idea to unroll this loop, let's do it!
    JITDUMP("\nUnrolling loop " FMT_LP " unrollCostSz = %d\n", loop->GetIndex(), unrollCostSz.Value());
    JITDUMPEXEC(FlowGraphNaturalLoop::Dump(loop));

    // We unroll a loop focused around the test and IV that was
    // identified by FlowGraphNaturalLoop::AnalyzeIteration. Note that:
    //
    // * The loop can have multiple exits. The exit guarded on the IV
    //   is the one we can optimize away when we unroll, since we know
    //   the value of the IV in each iteration. The other exits will
    //   remain in place in each iteration.
    //
    // * The loop can have multiple backedges. Often, there is a
    //   single backedge that becomes statically unreachable when we
    //   optimize the exit guarded on the IV. In that case the loop
    //   structure disappears. However, if there were multiple backedges,
    //   the loop structure can remain in each unrolled iteration.
    //
    // * The loop being unrolled can also have nested loops, which will
    //   be duplicated for each unrolled iteration.
    //
    // * Unrolling a loop creates or removes basic blocks, depending on
    //   whether the iter count is 0. When nested loops are unrolled,
    //   instead of trying to maintain the new right set of loop blocks
    //   that exist in all ancestor loops, we skip unrolling for all
    //   ancestor loops and instead recompute the loop structure and
    //   retry unrolling. It is rare to have multiple nested unrollings
    //   of loops, so this is not a TP issue.

    BlockToBlockMap blockMap(getAllocator(CMK_LoopUnroll));

    BasicBlock* bottom        = loop->GetLexicallyBottomMostBlock();
    BasicBlock* insertAfter   = bottom;
    BasicBlock* prevTestBlock = nullptr;
    unsigned    iterToUnroll  = totalIter; // The number of iterations left to unroll

    // Find the exit block of the IV test first. We need to do that
    // here since it may have implicit fallthrough that we'll change
    // below.
    BasicBlock* exiting = iterInfo.TestBlock;
    assert(exiting->KindIs(BBJ_COND));
    assert(loop->ContainsBlock(exiting->GetTrueTarget()) != loop->ContainsBlock(exiting->GetFalseTarget()));
    BasicBlock* exit =
        loop->ContainsBlock(exiting->GetTrueTarget()) ? exiting->GetFalseTarget() : exiting->GetTrueTarget();

    for (int lval = lbeg; iterToUnroll > 0; iterToUnroll--)
    {
        // Block weight should no longer have the loop multiplier
        //
        // Note this is not quite right, as we may not have upscaled by this amount
        // and we might not have upscaled at all, if we had profile data.
        //
        weight_t scaleWeight = 1.0 / BB_LOOP_WEIGHT_SCALE;
        loop->Duplicate(&insertAfter, &blockMap, scaleWeight);

        // Replace all uses of the loop iterator with the current value.
        loop->VisitLoopBlocks([=, &blockMap](BasicBlock* block) {
            optReplaceScalarUsesWithConst(blockMap[block], lvar, lval);
            return BasicBlockVisit::Continue;
        });

        // Remove the test we created in the duplicate; we're doing a full unroll.
        BasicBlock* testBlock = blockMap[iterInfo.TestBlock];

        optRedirectPrevUnrollIteration(loop, prevTestBlock, blockMap[loop->GetHeader()]);

        // Save the test block of the previously unrolled
        // iteration, so that we can redirect it when we create
        // the next iteration (or to the exit for the last
        // iteration).
        prevTestBlock = testBlock;

        // update the new value for the unrolled iterator

        switch (iterOper)
        {
            case GT_ADD:
                lval += iterInc;
                break;

            case GT_SUB:
                lval -= iterInc;
                break;

            default:
                unreached();
        }
    }

    // If we get here, we successfully cloned all the blocks in the
    // unrolled loop. Note we may not have done any cloning at all if
    // the loop iteration count was computed to be zero. Such loops are
    // guaranteed to be unreachable since if the repetition count is
    // zero the loop invariant is false on the first iteration, yet
    // FlowGraphNaturalLoop::AnalyzeIteration only returns true if the
    // loop invariant is true on every iteration. That means we have a
    // guarding check before we enter the loop that will always be
    // false.
    optRedirectPrevUnrollIteration(loop, prevTestBlock, exit);

    // The old loop body is unreachable now, but we will remove those
    // blocks after we finish unrolling.
    CLANG_FORMAT_COMMENT_ANCHOR;

#ifdef DEBUG
    if (verbose)
    {
        printf("Whole unrolled loop:\n");

        gtDispTree(iterInfo.InitTree);
        printf("\n");
        fgDumpTrees(bottom->Next(), insertAfter);
    }
#endif // DEBUG

    return true;
}

//-----------------------------------------------------------------------------
// optRedirectPrevUnrollIteration:
//   Redirect the previous unrolled loop iteration (or entry) to a new target.
//
// Parameters:
//   loop          - The loop that is being unrolled
//   prevTestBlock - The test block of the previous iteration, or nullptr if
//                   this is the first unrolled iteration.
//   target        - The new target for the previous iteration.
//
//
// Remarks:
//   If "prevTestBlock" is nullptr, then the entry edges of the loop are
//   redirected to the target. Otherwise "prevTestBlock" has its terminating
//   statement removed and is changed to a BBJ_ALWAYS that goes to the target.
//
void Compiler::optRedirectPrevUnrollIteration(FlowGraphNaturalLoop* loop, BasicBlock* prevTestBlock, BasicBlock* target)
{
    if (prevTestBlock != nullptr)
    {
        assert(prevTestBlock->KindIs(BBJ_COND));
        Statement* testCopyStmt = prevTestBlock->lastStmt();
        GenTree*   testCopyExpr = testCopyStmt->GetRootNode();
        assert(testCopyExpr->gtOper == GT_JTRUE);
        GenTree* sideEffList = nullptr;
        gtExtractSideEffList(testCopyExpr, &sideEffList, GTF_SIDE_EFFECT | GTF_ORDER_SIDEEFF);
        if (sideEffList == nullptr)
        {
            fgRemoveStmt(prevTestBlock, testCopyStmt);
        }
        else
        {
            testCopyStmt->SetRootNode(sideEffList);
        }

        fgRemoveRefPred(prevTestBlock->GetTrueTarget(), prevTestBlock);
        fgRemoveRefPred(prevTestBlock->GetFalseTarget(), prevTestBlock);

        // Redirect exit edge from previous iteration to new entry.
        prevTestBlock->SetKindAndTarget(BBJ_ALWAYS, target);
        fgAddRefPred(target, prevTestBlock);

        JITDUMP("Redirecting previously created exiting " FMT_BB " -> " FMT_BB "\n", prevTestBlock->bbNum,
                target->bbNum);
    }
    else
    {
        // Redirect all predecessors to the new one.
        for (FlowEdge* enterEdge : loop->EntryEdges())
        {
            BasicBlock* entering = enterEdge->getSourceBlock();
            JITDUMP("Redirecting " FMT_BB " -> " FMT_BB " to " FMT_BB " -> " FMT_BB "\n", entering->bbNum,
                    loop->GetHeader()->bbNum, entering->bbNum, target->bbNum);
            assert(!entering->KindIs(BBJ_COND)); // Ensured by canonicalization
            fgReplaceJumpTarget(entering, target, loop->GetHeader());
        }
    }
}

//-----------------------------------------------------------------------------
// optReplaceScalarUsesWithConst: Replace all GT_LCL_VAR occurrences of a local
// with a constant.
//
// Arguments:
//   block   - The block to replace in
//   lclNum  - The local to replace
//   cnsVal  - The constant to replace with
//
// Remarks:
//   This is used to replace the loop iterator with the constant value when
//   unrolling.
//
void Compiler::optReplaceScalarUsesWithConst(BasicBlock* block, unsigned lclNum, ssize_t cnsVal)
{
    class ReplaceVisitor final : public GenTreeVisitor<ReplaceVisitor>
    {
        unsigned m_lclNum;
        ssize_t  m_cnsVal;

    public:
        enum
        {
            DoPreOrder    = true,
            DoLclVarsOnly = true,
        };

        bool MadeChanges = false;

        ReplaceVisitor(Compiler* comp, unsigned lclNum, ssize_t cnsVal)
            : GenTreeVisitor(comp), m_lclNum(lclNum), m_cnsVal(cnsVal)
        {
        }

        fgWalkResult PreOrderVisit(GenTree** use, GenTree* user)
        {
            if ((*use)->OperIs(GT_LCL_VAR) && ((*use)->AsLclVarCommon()->GetLclNum() == m_lclNum))
            {
                *use        = m_compiler->gtNewIconNode(m_cnsVal, genActualType(*use));
                MadeChanges = true;
            }

            return fgWalkResult::WALK_CONTINUE;
        }
    };

    ReplaceVisitor visitor(this, lclNum, cnsVal);

    for (Statement* stmt : block->Statements())
    {
        visitor.WalkTree(stmt->GetRootNodePointer(), nullptr);

        if (visitor.MadeChanges)
        {
            // Replacing locals with constants can change whether we consider
            // something to have side effects. For example, `fgAddrCouldBeNull`
            // can switch from true to false if the address changes from
            // ADD(LCL_ADDR, LCL_VAR) -> ADD(LCL_ADDR, CNS_INT).
            gtUpdateStmtSideEffects(stmt);
            visitor.MadeChanges = false;
        }
    }
}

Compiler::OptInvertCountTreeInfoType Compiler::optInvertCountTreeInfo(GenTree* tree)
{
    class CountTreeInfoVisitor : public GenTreeVisitor<CountTreeInfoVisitor>
    {
    public:
        enum
        {
            DoPreOrder = true,
        };

        Compiler::OptInvertCountTreeInfoType Result = {};

        CountTreeInfoVisitor(Compiler* comp) : GenTreeVisitor(comp)
        {
        }

        fgWalkResult PreOrderVisit(GenTree** use, GenTree* user)
        {
            if (Compiler::IsSharedStaticHelper(*use))
            {
                Result.sharedStaticHelperCount++;
            }

            if ((*use)->OperIsArrLength())
            {
                Result.arrayLengthCount++;
            }

            return fgWalkResult::WALK_CONTINUE;
        }
    };

    CountTreeInfoVisitor walker(this);
    walker.WalkTree(&tree, nullptr);
    return walker.Result;
}

//-----------------------------------------------------------------------------
// optInvertWhileLoop: modify flow and duplicate code so that for/while loops are
//   entered at top and tested at bottom (aka loop rotation or bottom testing).
//   Creates a "zero trip test" condition which guards entry to the loop.
//   Enables loop invariant hoisting and loop cloning, which depend on
//   `do {} while` format loops. Enables creation of a pre-header block after the
//   zero trip test to place code that only runs if the loop is guaranteed to
//   run at least once.
//
// Arguments:
//   block -- block that may be the predecessor of the un-rotated loop's test block.
//
// Returns:
//   true if any IR changes possibly made (used to determine phase return status)
//
// Notes:
//   Uses a simple lexical screen to detect likely loops.
//
//   Specifically, we're looking for the following case:
//
//          ...
//          jmp test                // `block` argument
//   loop:
//          ...
//          ...
//   test:
//          ..stmts..
//          cond
//          jtrue loop
//
//   If we find this, and the condition is simple enough, we change
//   the loop to the following:
//
//          ...
//          ..stmts..               // duplicated cond block statements
//          cond                    // duplicated cond
//          jfalse done
//          // else fall-through
//   loop:
//          ...
//          ...
//   test:
//          ..stmts..
//          cond
//          jtrue loop
//   done:
//
//  Makes no changes if the flow pattern match fails.
//
//  May not modify a loop if profile is unfavorable, if the cost of duplicating
//  code is large (factoring in potential CSEs).
//
bool Compiler::optInvertWhileLoop(BasicBlock* block)
{
    assert(opts.OptimizationEnabled());
    assert(compCodeOpt() != SMALL_CODE);

    // Does the BB end with an unconditional jump?

    if (!block->KindIs(BBJ_ALWAYS) || block->JumpsToNext())
    {
        return false;
    }

    if (block->HasFlag(BBF_KEEP_BBJ_ALWAYS))
    {
        // It can't be one of the ones we use for our exception magic
        return false;
    }

    // Get hold of the jump target
    BasicBlock* const bTest = block->GetTarget();

    // Does the bTest consist of 'jtrue(cond) block' ?
    if (!bTest->KindIs(BBJ_COND))
    {
        return false;
    }

    // bTest must be a backwards jump to block->bbNext
    // This will be the top of the loop.
    //
    BasicBlock* const bTop = bTest->GetTrueTarget();

    if (!block->NextIs(bTop))
    {
        return false;
    }

    // Since bTest is a BBJ_COND it will have a bbFalseTarget
    //
    BasicBlock* const bJoin = bTest->GetFalseTarget();
    noway_assert(bJoin != nullptr);

    // 'block' must be in the same try region as the condition, since we're going to insert a duplicated condition
    // in a new block after 'block', and the condition might include exception throwing code.
    // On non-funclet platforms (x86), the catch exit is a BBJ_ALWAYS, but we don't want that to
    // be considered as the head of a loop, so also disallow different handler regions.
    if (!BasicBlock::sameEHRegion(block, bTest))
    {
        return false;
    }

    // The duplicated condition block will branch to bTest->GetFalseTarget(), so that also better be in the
    // same try region (or no try region) to avoid generating illegal flow.
    if (bJoin->hasTryIndex() && !BasicBlock::sameTryRegion(block, bJoin))
    {
        return false;
    }

    // It has to be a forward jump. Defer this check until after all the cheap checks
    // are done, since it iterates forward in the block list looking for bbTarget.
    //  TODO-CQ: Check if we can also optimize the backwards jump as well.
    //
    if (!fgIsForwardBranch(block, block->GetTarget()))
    {
        return false;
    }

    // Find the loop termination test at the bottom of the loop.
    Statement* const condStmt = bTest->lastStmt();

    // Verify the test block ends with a conditional that we can manipulate.
    GenTree* const condTree = condStmt->GetRootNode();
    noway_assert(condTree->gtOper == GT_JTRUE);
    if (!condTree->AsOp()->gtOp1->OperIsCompare())
    {
        return false;
    }

    JITDUMP("Matched flow pattern for loop inversion: block " FMT_BB " bTop " FMT_BB " bTest " FMT_BB "\n",
            block->bbNum, bTop->bbNum, bTest->bbNum);

    // Estimate the cost of cloning the entire test block.
    //
    // Note: it would help throughput to compute the maximum cost
    // first and early out for large bTest blocks, as we are doing two
    // tree walks per tree. But because of this helper call scan, the
    // maximum cost depends on the trees in the block.
    //
    // We might consider flagging blocks with hoistable helper calls
    // during importation, so we can avoid the helper search and
    // implement an early bail out for large blocks with no helper calls.
    //
    // Note that gtPrepareCost can cause operand swapping, so we must
    // return `true` (possible IR change) from here on.

    unsigned estDupCostSz = 0;

    for (Statement* const stmt : bTest->Statements())
    {
        GenTree* tree = stmt->GetRootNode();
        gtPrepareCost(tree);
        estDupCostSz += tree->GetCostSz();
    }

    weight_t       loopIterations            = BB_LOOP_WEIGHT_SCALE;
    bool           allProfileWeightsAreValid = false;
    weight_t const weightBlock               = block->bbWeight;
    weight_t const weightTest                = bTest->bbWeight;
    weight_t const weightTop                 = bTop->bbWeight;

    // If we have profile data then we calculate the number of times
    // the loop will iterate into loopIterations
    if (fgIsUsingProfileWeights())
    {
        // Only rely upon the profile weight when all three of these blocks
        // have good profile weights
        if (block->hasProfileWeight() && bTest->hasProfileWeight() && bTop->hasProfileWeight())
        {
            // If this while loop never iterates then don't bother transforming
            //
            if (weightTop == BB_ZERO_WEIGHT)
            {
                return true;
            }

            // We generally expect weightTest > weightTop
            //
            // Tolerate small inconsistencies...
            //
            if (!fgProfileWeightsConsistent(weightBlock + weightTop, weightTest))
            {
                JITDUMP("Profile weights locally inconsistent: block " FMT_WT ", next " FMT_WT ", test " FMT_WT "\n",
                        weightBlock, weightTop, weightTest);
            }
            else
            {
                allProfileWeightsAreValid = true;

                // Determine average iteration count
                //
                //   weightTop is the number of time this loop executes
                //   weightTest is the number of times that we consider entering or remaining in the loop
                //   loopIterations is the average number of times that this loop iterates
                //
                weight_t loopEntries = weightTest - weightTop;

                // If profile is inaccurate, try and use other data to provide a credible estimate.
                // The value should at least be >= weightBlock.
                //
                if (loopEntries < weightBlock)
                {
                    loopEntries = weightBlock;
                }

                loopIterations = weightTop / loopEntries;
            }
        }
        else
        {
            JITDUMP("Missing profile data for loop!\n");
        }
    }

    unsigned maxDupCostSz = 34;

    if ((compCodeOpt() == FAST_CODE) || compStressCompile(STRESS_DO_WHILE_LOOPS, 30))
    {
        maxDupCostSz *= 4;
    }

    // If this loop iterates a lot then raise the maxDupCost
    if (loopIterations >= 12.0)
    {
        maxDupCostSz *= 2;
        if (loopIterations >= 96.0)
        {
            maxDupCostSz *= 2;
        }
    }

    // If the compare has too high cost then we don't want to dup.

    bool costIsTooHigh = (estDupCostSz > maxDupCostSz);

    OptInvertCountTreeInfoType optInvertTotalInfo = {};
    if (costIsTooHigh)
    {
        // If we already know that the cost is acceptable, then don't waste time walking the tree
        // counting things to boost the maximum allowed cost.
        //
        // If the loop condition has a shared static helper, we really want this loop converted
        // as not converting the loop will disable loop hoisting, meaning the shared helper will
        // be executed on every loop iteration.
        //
        // If the condition has array.Length operations, also boost, as they are likely to be CSE'd.

        for (Statement* const stmt : bTest->Statements())
        {
            GenTree* tree = stmt->GetRootNode();

            OptInvertCountTreeInfoType optInvertInfo = optInvertCountTreeInfo(tree);
            optInvertTotalInfo.sharedStaticHelperCount += optInvertInfo.sharedStaticHelperCount;
            optInvertTotalInfo.arrayLengthCount += optInvertInfo.arrayLengthCount;

            if ((optInvertInfo.sharedStaticHelperCount > 0) || (optInvertInfo.arrayLengthCount > 0))
            {
                // Calculate a new maximum cost. We might be able to early exit.

                unsigned newMaxDupCostSz =
                    maxDupCostSz + 24 * min(optInvertTotalInfo.sharedStaticHelperCount, (int)(loopIterations + 1.5)) +
                    8 * optInvertTotalInfo.arrayLengthCount;

                // Is the cost too high now?
                costIsTooHigh = (estDupCostSz > newMaxDupCostSz);
                if (!costIsTooHigh)
                {
                    // No need counting any more trees; we're going to do the transformation.
                    JITDUMP("Decided to duplicate loop condition block after counting helpers in tree [%06u] in "
                            "block " FMT_BB,
                            dspTreeID(tree), bTest->bbNum);
                    maxDupCostSz = newMaxDupCostSz; // for the JitDump output below
                    break;
                }
            }
        }
    }

#ifdef DEBUG
    if (verbose)
    {
        // Note that `optInvertTotalInfo.sharedStaticHelperCount = 0` means either there were zero helpers, or the
        // tree walk to count them was not done.
        printf(
            "\nDuplication of loop condition [%06u] is %s, because the cost of duplication (%i) is %s than %i,"
            "\n   loopIterations = %7.3f, optInvertTotalInfo.sharedStaticHelperCount >= %d, validProfileWeights = %s\n",
            dspTreeID(condTree), costIsTooHigh ? "not done" : "performed", estDupCostSz,
            costIsTooHigh ? "greater" : "less or equal", maxDupCostSz, loopIterations,
            optInvertTotalInfo.sharedStaticHelperCount, dspBool(allProfileWeightsAreValid));
    }
#endif

    if (costIsTooHigh)
    {
        return true;
    }

    bool foundCondTree = false;

    // Create a new block after `block` to put the copied condition code.
    BasicBlock* bNewCond = fgNewBBafter(BBJ_COND, block, /*extendRegion*/ true, bJoin);
    block->SetKindAndTarget(BBJ_ALWAYS, bNewCond);
    block->SetFlags(BBF_NONE_QUIRK);
    assert(block->JumpsToNext());

    // Clone each statement in bTest and append to bNewCond.
    for (Statement* const stmt : bTest->Statements())
    {
        GenTree* originalTree = stmt->GetRootNode();
        GenTree* clonedTree   = gtCloneExpr(originalTree);

        // Special case handling needed for the conditional jump tree
        if (originalTree == condTree)
        {
            foundCondTree = true;

            // Get the compare subtrees
            GenTree* originalCompareTree = originalTree->AsOp()->gtOp1;
            GenTree* clonedCompareTree   = clonedTree->AsOp()->gtOp1;
            assert(originalCompareTree->OperIsCompare());
            assert(clonedCompareTree->OperIsCompare());

            // Flag compare and cloned copy so later we know this loop
            // has a proper zero trip test.
            originalCompareTree->gtFlags |= GTF_RELOP_ZTT;
            clonedCompareTree->gtFlags |= GTF_RELOP_ZTT;

            // The original test branches to remain in the loop.  The
            // new cloned test will branch to avoid the loop.  So the
            // cloned compare needs to reverse the branch condition.
            gtReverseCond(clonedCompareTree);
        }

        Statement* clonedStmt = fgNewStmtAtEnd(bNewCond, clonedTree);

        if (opts.compDbgInfo)
        {
            clonedStmt->SetDebugInfo(stmt->GetDebugInfo());
        }
    }

    assert(foundCondTree);

    // Flag the block that received the copy as potentially having various constructs.
    bNewCond->CopyFlags(bTest, BBF_COPY_PROPAGATE);

    // Fix flow and profile
    //
    bNewCond->inheritWeight(block);

    if (allProfileWeightsAreValid)
    {
        weight_t const delta = weightTest - weightTop;

        // If there is just one outside edge incident on bTest, then ideally delta == block->bbWeight.
        // But this might not be the case if profile data is inconsistent.
        //
        // And if bTest has multiple outside edges we want to account for the weight of them all.
        //
        if (delta > block->bbWeight)
        {
            bNewCond->setBBProfileWeight(delta);
        }
    }

    // Update pred info
    //
    bNewCond->SetFalseTarget(bTop);
    fgAddRefPred(bJoin, bNewCond);
    fgAddRefPred(bTop, bNewCond);

    fgAddRefPred(bNewCond, block);
    fgRemoveRefPred(bTest, block);

    // Move all predecessor edges that look like loop entry edges to point to the new cloned condition
    // block, not the existing condition block. The idea is that if we only move `block` to point to
    // `bNewCond`, but leave other `bTest` predecessors still pointing to `bTest`, when we eventually
    // recognize loops, the loop will appear to have multiple entries, which will prevent optimization.
    // We don't have loops yet, but blocks should be in increasing lexical numbered order, so use that
    // as the proxy for predecessors that are "in" versus "out" of the potential loop. Note that correctness
    // is maintained no matter which condition block we point to, but we'll lose optimization potential
    // (and create spaghetti code) if we get it wrong.
    //
    BlockToBlockMap blockMap(getAllocator(CMK_LoopOpt));
    bool            blockMapInitialized = false;

    unsigned const loopFirstNum  = bTop->bbNum;
    unsigned const loopBottomNum = bTest->bbNum;
    for (BasicBlock* const predBlock : bTest->PredBlocks())
    {
        unsigned const bNum = predBlock->bbNum;
        if ((loopFirstNum <= bNum) && (bNum <= loopBottomNum))
        {
            // Looks like the predecessor is from within the potential loop; skip it.
            continue;
        }

        if (!blockMapInitialized)
        {
            blockMapInitialized = true;
            blockMap.Set(bTest, bNewCond);
        }

        // Redirect the predecessor to the new block.
        JITDUMP("Redirecting non-loop " FMT_BB " -> " FMT_BB " to " FMT_BB " -> " FMT_BB "\n", predBlock->bbNum,
                bTest->bbNum, predBlock->bbNum, bNewCond->bbNum);
        optRedirectBlock(predBlock, &blockMap, RedirectBlockOption::UpdatePredLists);
    }

    // If we have profile data for all blocks and we know that we are cloning the
    // `bTest` block into `bNewCond` and thus changing the control flow from `block` so
    // that it no longer goes directly to `bTest` anymore, we have to adjust
    // various weights.
    //
    if (allProfileWeightsAreValid)
    {
        // Update the weight for bTest. Normally, this reduces the weight of the bTest, except in odd
        // cases of stress modes with inconsistent weights.
        //
        JITDUMP("Reducing profile weight of " FMT_BB " from " FMT_WT " to " FMT_WT "\n", bTest->bbNum, weightTest,
                weightTop);
        bTest->inheritWeight(bTop);

        // Determine the new edge weights.
        //
        // We project the next/jump ratio for block and bTest by using
        // the original likelihoods out of bTest.
        //
        // Note "next" is the loop top block, not bTest's bbNext,
        // we'll call this latter block "after".
        //
        weight_t const testToNextLikelihood  = min(1.0, weightTop / weightTest);
        weight_t const testToAfterLikelihood = 1.0 - testToNextLikelihood;

        // Adjust edges out of bTest (which now has weight weightTop)
        //
        weight_t const testToNextWeight  = weightTop * testToNextLikelihood;
        weight_t const testToAfterWeight = weightTop * testToAfterLikelihood;

        FlowEdge* const edgeTestToNext  = fgGetPredForBlock(bTop, bTest);
        FlowEdge* const edgeTestToAfter = fgGetPredForBlock(bTest->GetFalseTarget(), bTest);

        JITDUMP("Setting weight of " FMT_BB " -> " FMT_BB " to " FMT_WT " (iterate loop)\n", bTest->bbNum, bTop->bbNum,
                testToNextWeight);
        JITDUMP("Setting weight of " FMT_BB " -> " FMT_BB " to " FMT_WT " (exit loop)\n", bTest->bbNum,
                bTest->Next()->bbNum, testToAfterWeight);

        edgeTestToNext->setEdgeWeights(testToNextWeight, testToNextWeight, bTop);
        edgeTestToAfter->setEdgeWeights(testToAfterWeight, testToAfterWeight, bTest->GetFalseTarget());

        // Adjust edges out of block, using the same distribution.
        //
        JITDUMP("Profile weight of " FMT_BB " remains unchanged at " FMT_WT "\n", block->bbNum, weightBlock);

        weight_t const blockToNextLikelihood  = testToNextLikelihood;
        weight_t const blockToAfterLikelihood = testToAfterLikelihood;

        weight_t const blockToNextWeight  = weightBlock * blockToNextLikelihood;
        weight_t const blockToAfterWeight = weightBlock * blockToAfterLikelihood;

        FlowEdge* const edgeBlockToNext  = fgGetPredForBlock(bNewCond->GetFalseTarget(), bNewCond);
        FlowEdge* const edgeBlockToAfter = fgGetPredForBlock(bNewCond->GetTrueTarget(), bNewCond);

        JITDUMP("Setting weight of " FMT_BB " -> " FMT_BB " to " FMT_WT " (enter loop)\n", bNewCond->bbNum,
                bNewCond->GetFalseTarget()->bbNum, blockToNextWeight);
        JITDUMP("Setting weight of " FMT_BB " -> " FMT_BB " to " FMT_WT " (avoid loop)\n", bNewCond->bbNum,
                bNewCond->GetTrueTarget()->bbNum, blockToAfterWeight);

        edgeBlockToNext->setEdgeWeights(blockToNextWeight, blockToNextWeight, bNewCond->GetFalseTarget());
        edgeBlockToAfter->setEdgeWeights(blockToAfterWeight, blockToAfterWeight, bNewCond->GetTrueTarget());

#ifdef DEBUG
        // If we're checkig profile data, see if profile for the two target blocks is consistent.
        //
        if ((activePhaseChecks & PhaseChecks::CHECK_PROFILE) == PhaseChecks::CHECK_PROFILE)
        {
            const ProfileChecks checks        = (ProfileChecks)JitConfig.JitProfileChecks();
            const bool          nextProfileOk = fgDebugCheckIncomingProfileData(bNewCond->GetFalseTarget(), checks);
            const bool          jumpProfileOk = fgDebugCheckIncomingProfileData(bNewCond->GetTrueTarget(), checks);

            if (hasFlag(checks, ProfileChecks::RAISE_ASSERT))
            {
                assert(nextProfileOk);
                assert(jumpProfileOk);
            }
        }
#endif // DEBUG
    }

#ifdef DEBUG
    if (verbose)
    {
        printf("\nDuplicated loop exit block at " FMT_BB " for loop (" FMT_BB " - " FMT_BB ")\n", bNewCond->bbNum,
               bNewCond->GetFalseTarget()->bbNum, bTest->bbNum);
        printf("Estimated code size expansion is %d\n", estDupCostSz);

        fgDumpBlock(bNewCond);
        fgDumpBlock(bTest);
    }
#endif // DEBUG

    return true;
}

//-----------------------------------------------------------------------------
// optInvertLoops: invert while loops in the method
//
// Returns:
//   suitable phase status
//
PhaseStatus Compiler::optInvertLoops()
{
    noway_assert(opts.OptimizationEnabled());
    noway_assert(fgModified == false);

#if defined(OPT_CONFIG)
    if (!JitConfig.JitDoLoopInversion())
    {
        JITDUMP("Loop inversion disabled\n");
        return PhaseStatus::MODIFIED_NOTHING;
    }
#endif // OPT_CONFIG

    bool madeChanges = fgRenumberBlocks();

    if (compCodeOpt() == SMALL_CODE)
    {
        // do not invert any loops
    }
    else
    {
        for (BasicBlock* const block : Blocks())
        {
            // Make sure the appropriate fields are initialized
            //
            if (block->bbWeight == BB_ZERO_WEIGHT)
            {
                // Zero weighted block can't have a LOOP_HEAD flag
                noway_assert(block->isLoopHead() == false);
                continue;
            }

            if (optInvertWhileLoop(block))
            {
                madeChanges = true;
            }
        }
    }

    if (fgModified)
    {
        // Reset fgModified here as we've done a consistent set of edits.
        //
        fgModified = false;
    }

    return madeChanges ? PhaseStatus::MODIFIED_EVERYTHING : PhaseStatus::MODIFIED_NOTHING;
}

//-----------------------------------------------------------------------------
// optOptimizeFlow: simplify flow graph
//
// Returns:
//   suitable phase status
//
// Notes:
//   Does not do profile-based reordering to try and ensure that
//   that we recognize and represent as many loops as possible.
//
PhaseStatus Compiler::optOptimizeFlow()
{
    noway_assert(opts.OptimizationEnabled());
    noway_assert(fgModified == false);

    fgUpdateFlowGraph(/* doTailDuplication */ true);
    fgReorderBlocks(/* useProfile */ false);

    // fgReorderBlocks can cause IR changes even if it does not modify
    // the flow graph. It calls gtPrepareCost which can cause operand swapping.
    // Work around this for now.
    //
    // Note phase status only impacts dumping and checking done post-phase,
    // it has no impact on a release build.
    //
    return PhaseStatus::MODIFIED_EVERYTHING;
}

//-----------------------------------------------------------------------------
// optOptimizeLayout: reorder blocks to reduce cost of control flow
//
// Returns:
//   suitable phase status
//
// Notes:
//   Reorders using profile data, if available.
//
PhaseStatus Compiler::optOptimizeLayout()
{
    noway_assert(opts.OptimizationEnabled());

    fgUpdateFlowGraph(/* doTailDuplication */ false);
    fgReorderBlocks(/* useProfile */ true);
    fgUpdateFlowGraph(/* doTailDuplication */ false, /* isPhase */ false);

    // fgReorderBlocks can cause IR changes even if it does not modify
    // the flow graph. It calls gtPrepareCost which can cause operand swapping.
    // Work around this for now.
    //
    // Note phase status only impacts dumping and checking done post-phase,
    // it has no impact on a release build.
    //
    return PhaseStatus::MODIFIED_EVERYTHING;
}

//------------------------------------------------------------------------
// optMarkLoopHeads: Mark all potential loop heads as BBF_LOOP_HEAD. A potential loop head is a block
// targeted by a lexical back edge, where the source of the back edge is reachable from the block.
// Note that if there are no lexical back edges, there can't be any loops.
//
// If there are any potential loop heads, set `fgHasLoops` to `true`.
//
// Assumptions:
//    The reachability sets must be computed and valid.
//
void Compiler::optMarkLoopHeads()
{
#ifdef DEBUG
    if (verbose)
    {
        printf("*************** In optMarkLoopHeads()\n");
    }

    assert(m_reachabilitySets != nullptr);
    fgDebugCheckBBNumIncreasing();

    int loopHeadsMarked = 0;
#endif

    bool hasLoops = false;

    for (BasicBlock* const block : Blocks())
    {
        // Set BBF_LOOP_HEAD if we have backwards branches to this block.

        for (BasicBlock* const predBlock : block->PredBlocks())
        {
            if (block->bbNum <= predBlock->bbNum)
            {
                if (predBlock->KindIs(BBJ_CALLFINALLY))
                {
                    // Loops never have BBJ_CALLFINALLY as the source of their "back edge".
                    continue;
                }

                // If block can reach predBlock then we have a loop head
                if (m_reachabilitySets->CanReach(block, predBlock))
                {
                    hasLoops = true;
                    block->SetFlags(BBF_LOOP_HEAD);
                    INDEBUG(++loopHeadsMarked);
                    break; // No need to look at more `block` predecessors
                }
            }
        }
    }

    JITDUMP("%d loop heads marked\n", loopHeadsMarked);
    fgHasLoops = hasLoops;
}

//-----------------------------------------------------------------------------
// optResetLoopInfo: reset all loop info in preparation for refinding the loops
// and scaling blocks based on it.
//
void Compiler::optResetLoopInfo()
{
#ifdef DEBUG
    if (verbose)
    {
        printf("*************** In optResetLoopInfo()\n");
    }
#endif

    for (BasicBlock* const block : Blocks())
    {
        // If the block weight didn't come from profile data, reset it so it can be calculated again.
        if (!block->hasProfileWeight())
        {
            block->bbWeight = BB_UNITY_WEIGHT;
            block->RemoveFlags(BBF_RUN_RARELY);
        }

        block->RemoveFlags(BBF_LOOP_HEAD);
    }
}

//-----------------------------------------------------------------------------
// optFindAndScaleGeneralLoopBlocks: scale block weights based on loop nesting depth.
// Note that this uses a very general notion of "loop": any block targeted by a reachable
// back-edge is considered a loop.
//
void Compiler::optFindAndScaleGeneralLoopBlocks()
{
#ifdef DEBUG
    if (verbose)
    {
        printf("*************** In optFindAndScaleGeneralLoopBlocks()\n");
    }
#endif

    // This code depends on block number ordering.
    INDEBUG(fgDebugCheckBBNumIncreasing());

    assert(m_dfsTree != nullptr);
    if (m_reachabilitySets == nullptr)
    {
        m_reachabilitySets = BlockReachabilitySets::Build(m_dfsTree);
    }
    if (m_domTree == nullptr)
    {
        m_domTree = FlowGraphDominatorTree::Build(m_dfsTree);
    }

    unsigned generalLoopCount = 0;

    // We will use the following terminology:
    // top        - the first basic block in the loop (i.e. the head of the backward edge)
    // bottom     - the last block in the loop (i.e. the block from which we jump to the top)
    // lastBottom - used when we have multiple back edges to the same top

    for (BasicBlock* const top : Blocks())
    {
        // Only consider `top` blocks already determined to be potential loop heads.
        if (!top->isLoopHead())
        {
            continue;
        }

        BasicBlock* foundBottom = nullptr;

        for (BasicBlock* const bottom : top->PredBlocks())
        {
            // Is this a loop candidate? - We look for "back edges"

            // Is this a backward edge? (from BOTTOM to TOP)
            if (top->bbNum > bottom->bbNum)
            {
                continue;
            }

            // We only consider back-edges of these kinds for loops.
            if (!bottom->KindIs(BBJ_COND, BBJ_ALWAYS, BBJ_CALLFINALLYRET))
            {
                continue;
            }

            /* the top block must be able to reach the bottom block */
            if (!m_reachabilitySets->CanReach(top, bottom))
            {
                continue;
            }

            /* Found a new loop, record the longest backedge in foundBottom */

            if ((foundBottom == nullptr) || (bottom->bbNum > foundBottom->bbNum))
            {
                foundBottom = bottom;
            }
        }

        if (foundBottom)
        {
            generalLoopCount++;

            /* Mark all blocks between 'top' and 'bottom' */

            optScaleLoopBlocks(top, foundBottom);
        }

        // We track at most 255 loops
        if (generalLoopCount == 255)
        {
#if COUNT_LOOPS
            totalUnnatLoopOverflows++;
#endif
            break;
        }
    }

    JITDUMP("\nFound a total of %d general loops.\n", generalLoopCount);

#if COUNT_LOOPS
    totalUnnatLoopCount += generalLoopCount;
#endif
}

//-----------------------------------------------------------------------------
// optFindLoops: find loops in the function.
//
// The JIT recognizes two types of loops in a function: natural loops and "general" (or "unnatural") loops.
// Natural loops are those which get added to Compiler::m_loops. Most downstream optimizations require
// using natural loops. See `FlowGraphNaturalLoop` for a definition of the criteria satisfied by a natural loop.
// A general loop is defined as a lexical (program order) range of blocks where a later block branches to an
// earlier block (that is, there is a back edge in the flow graph), and the later block is reachable from the earlier
// block. General loops are used for weighting flow graph blocks (when there is no block profile data).
//
// Notes:
//  Also (re)sets all non-IBC block weights.
//
PhaseStatus Compiler::optFindLoopsPhase()
{
#ifdef DEBUG
    if (verbose)
    {
        printf("*************** In optFindLoopsPhase()\n");
    }
#endif

    optMarkLoopHeads();

    assert(m_dfsTree != nullptr);
    optFindLoops();

    if (fgHasLoops)
    {
        optFindAndScaleGeneralLoopBlocks();
    }

    optNumNaturalLoopsFound = (unsigned)m_loops->NumLoops();

    return PhaseStatus::MODIFIED_EVERYTHING;
}

//-----------------------------------------------------------------------------
// optFindLoops: Find, compact and canonicalize natural loops.
//
void Compiler::optFindLoops()
{
    m_loops = FlowGraphNaturalLoops::Find(m_dfsTree);

    optCompactLoops();

    if (optCanonicalizeLoops())
    {
        fgInvalidateDfsTree();
        m_dfsTree = fgComputeDfs();
        m_loops   = FlowGraphNaturalLoops::Find(m_dfsTree);
    }

    fgRenumberBlocks();

    // Starting now, we require all loops to have pre-headers.
    optLoopsRequirePreHeaders = true;

    // Leave a bread crumb for future phases like loop alignment about whether
    // looking for loops makes sense. We generally do not expect phases to
    // introduce new cycles/loops in the flow graph; if they do, they should
    // set this to true themselves.
    // We use more general cycles over "m_loops->NumLoops() > 0" here because
    // future optimizations can easily cause general cycles to become natural
    // loops by removing edges.
    fgMightHaveNaturalLoops = m_dfsTree->HasCycle();
    assert(fgMightHaveNaturalLoops || (m_loops->NumLoops() == 0));
}

//-----------------------------------------------------------------------------
// optCanonicalizeLoops: Canonicalize natural loops.
//
// Parameters:
//   loops - Structure containing loops
//
// Returns:
//   True if any flow graph modifications were made
//
// Remarks:
//   Guarantees that all natural loops have preheaders.
//
bool Compiler::optCanonicalizeLoops()
{
    bool changed = false;
    for (FlowGraphNaturalLoop* loop : m_loops->InReversePostOrder())
    {
        changed |= optCreatePreheader(loop);
    }

    return changed;
}

//-----------------------------------------------------------------------------
// optCompactLoops: Compact loops to make their loop blocks lexical if possible.
//
void Compiler::optCompactLoops()
{
    for (FlowGraphNaturalLoop* loop : m_loops->InReversePostOrder())
    {
        optCompactLoop(loop);
    }
}

//-----------------------------------------------------------------------------
// optCompactLoop: Compact a specific loop.
//
// Parameters:
//   loop - The loop
//
void Compiler::optCompactLoop(FlowGraphNaturalLoop* loop)
{
    BasicBlock* insertionPoint = nullptr;

    BasicBlock* top           = loop->GetLexicallyTopMostBlock();
    unsigned    numLoopBlocks = loop->NumLoopBlocks();

    BasicBlock* cur = top;
    while (numLoopBlocks > 0)
    {
        if (loop->ContainsBlock(cur))
        {
            numLoopBlocks--;
            cur = cur->Next();
            continue;
        }

        // If this is a CALLFINALLYRET that is not in the loop, but the
        // CALLFINALLY was, then we have to leave it in place. For compaction
        // purposes this doesn't really make any difference, since no codegen
        // is associated with the CALLFINALLYRET anyway.
        if (cur->isBBCallFinallyPairTail())
        {
            cur = cur->Next();
            continue;
        }

        BasicBlock* lastNonLoopBlock = cur;
        while (true)
        {
            // Should always have a "bottom" block of the loop where we stop.
            assert(lastNonLoopBlock->Next() != nullptr);
            if (loop->ContainsBlock(lastNonLoopBlock->Next()))
            {
                break;
            }

            lastNonLoopBlock = lastNonLoopBlock->Next();
        }

        if (insertionPoint == nullptr)
        {
            insertionPoint = optFindLoopCompactionInsertionPoint(loop, top);
        }

        BasicBlock* previous      = cur->Prev();
        BasicBlock* nextLoopBlock = lastNonLoopBlock->Next();
        assert(previous != nullptr);
        if (!BasicBlock::sameEHRegion(previous, nextLoopBlock) || !BasicBlock::sameEHRegion(previous, insertionPoint))
        {
            // EH regions would be ill-formed if we moved these blocks out.
            cur = nextLoopBlock;
            continue;
        }

        // Now physically move the blocks.
        BasicBlock* moveBefore = insertionPoint->Next();

        fgUnlinkRange(cur, lastNonLoopBlock);
        fgMoveBlocksAfter(cur, lastNonLoopBlock, insertionPoint);
        ehUpdateLastBlocks(insertionPoint, lastNonLoopBlock);

        // Update insertionPoint for the next insertion.
        insertionPoint = lastNonLoopBlock;

        cur = nextLoopBlock;
    }
}

//-----------------------------------------------------------------------------
// optFindLoopCompactionInsertionPoint: Find a good insertion point at which to
// move blocks from the lexical range of "loop" that is not part of the loop.
//
// Parameters:
//   loop - The loop
//   top  - Lexical top block of the loop.
//
// Returns:
//   Non-null insertion point.
//
BasicBlock* Compiler::optFindLoopCompactionInsertionPoint(FlowGraphNaturalLoop* loop, BasicBlock* top)
{
    // Find an insertion point for blocks we're going to move.  Move them down
    // out of the loop, and if possible find a spot that won't break up fall-through.
    BasicBlock* bottom         = loop->GetLexicallyBottomMostBlock();
    BasicBlock* insertionPoint = bottom;
    while (insertionPoint->bbFallsThrough() && !insertionPoint->IsLast())
    {
        // Keep looking for a better insertion point if we can.
        BasicBlock* newInsertionPoint = optTryAdvanceLoopCompactionInsertionPoint(loop, insertionPoint, top, bottom);
        if (newInsertionPoint == nullptr)
        {
            // Ran out of candidate insertion points, so just split up the fall-through.
            break;
        }

        insertionPoint = newInsertionPoint;
    }

    return insertionPoint;
}

//-----------------------------------------------------------------------------
// optTryAdvanceLoopCompactionInsertionPoint: Advance the insertion point to
// avoid having to insert new blocks due to fallthrough.
//
// Parameters:
//   loop           - The loop
//   insertionPoint - Current insertion point
//   top            - Lexical top block of the loop.
//   bottom         - Lexical bottom block of the loop.
//
// Returns:
//   New insertion point.
//
BasicBlock* Compiler::optTryAdvanceLoopCompactionInsertionPoint(FlowGraphNaturalLoop* loop,
                                                                BasicBlock*           insertionPoint,
                                                                BasicBlock*           top,
                                                                BasicBlock*           bottom)
{
    BasicBlock* newInsertionPoint = insertionPoint->Next();

    if (!BasicBlock::sameEHRegion(insertionPoint, newInsertionPoint))
    {
        // Don't cross an EH region boundary.
        return nullptr;
    }

    // TODO-Quirk: Compatibility with old compaction
    if (newInsertionPoint->KindIs(BBJ_ALWAYS, BBJ_COND))
    {
        BasicBlock* dest =
            newInsertionPoint->KindIs(BBJ_ALWAYS) ? newInsertionPoint->GetTarget() : newInsertionPoint->GetTrueTarget();
        if ((dest->bbNum >= top->bbNum) && (dest->bbNum <= bottom->bbNum) && !loop->ContainsBlock(dest))
        {
            return nullptr;
        }
    }

    // TODO-Quirk: Compatibility with old compaction
    for (BasicBlock* const predBlock : newInsertionPoint->PredBlocks())
    {
        if ((predBlock->bbNum >= top->bbNum) && (predBlock->bbNum <= bottom->bbNum) && !loop->ContainsBlock(predBlock))
        {
            // Don't make this forward edge a backwards edge.
            return nullptr;
        }
    }

    // Compaction runs on outer loops before inner loops. That means all
    // unlexical blocks here are part of an ancestor loop (or trivial
    // BBJ_ALWAYS exit blocks). To avoid breaking lexicality of ancestor loops
    // we avoid moving any block past the bottom of an ancestor loop.
    for (FlowGraphNaturalLoop* ancestor = loop->GetParent(); ancestor != nullptr; ancestor = ancestor->GetParent())
    {
        if (newInsertionPoint == ancestor->GetLexicallyBottomMostBlock())
        {
            return nullptr;
        }
    }

    // Advancing the insertion point is ok, except that we can't split up any call finally
    // pair, so if we've got such a pair recurse to see if we can move past the whole thing.
    return newInsertionPoint->isBBCallFinallyPair()
               ? optTryAdvanceLoopCompactionInsertionPoint(loop, newInsertionPoint, top, bottom)
               : newInsertionPoint;
}

//-----------------------------------------------------------------------------
// optCreatePreheader: Create (or find) a preheader for a natural loop.
//
// Parameters:
//   loop - The loop to create the preheader for
//
// Returns:
//   True if a new preheader block had to be created.
//
bool Compiler::optCreatePreheader(FlowGraphNaturalLoop* loop)
{
    BasicBlock* header = loop->GetHeader();

    // If the header is already a try entry then we need to keep it as such
    // since blocks from within the loop will be jumping back to it after we're
    // done. Thus, in that case we insert the preheader in the enclosing try
    // region.
    unsigned headerEHRegion    = header->hasTryIndex() ? header->getTryIndex() : EHblkDsc::NO_ENCLOSING_INDEX;
    unsigned preheaderEHRegion = headerEHRegion;
    if ((headerEHRegion != EHblkDsc::NO_ENCLOSING_INDEX) && bbIsTryBeg(header))
    {
        preheaderEHRegion = ehTrueEnclosingTryIndexIL(headerEHRegion);
    }

    if (!bbIsHandlerBeg(header) && (loop->EntryEdges().size() == 1))
    {
        BasicBlock* preheaderCandidate = loop->EntryEdges()[0]->getSourceBlock();
        unsigned    candidateEHRegion =
            preheaderCandidate->hasTryIndex() ? preheaderCandidate->getTryIndex() : EHblkDsc::NO_ENCLOSING_INDEX;
        if (preheaderCandidate->KindIs(BBJ_ALWAYS) && preheaderCandidate->TargetIs(loop->GetHeader()) &&
            (candidateEHRegion == preheaderEHRegion))
        {
            JITDUMP("Natural loop " FMT_LP " already has preheader " FMT_BB "\n", loop->GetIndex(),
                    preheaderCandidate->bbNum);
            return false;
        }
    }

    BasicBlock* insertBefore = loop->GetLexicallyTopMostBlock();
    if (!BasicBlock::sameEHRegion(insertBefore, header))
    {
        insertBefore = header;
    }

    BasicBlock* preheader = fgNewBBbefore(BBJ_ALWAYS, insertBefore, false, header);
    preheader->SetFlags(BBF_INTERNAL);
    fgSetEHRegionForNewPreheader(preheader);

    if (preheader->NextIs(header))
    {
        preheader->SetFlags(BBF_NONE_QUIRK);
    }

    preheader->bbCodeOffs = insertBefore->bbCodeOffs;

    JITDUMP("Created new preheader " FMT_BB " for " FMT_LP "\n", preheader->bbNum, loop->GetIndex());

    fgAddRefPred(header, preheader);

    for (FlowEdge* enterEdge : loop->EntryEdges())
    {
        BasicBlock* enterBlock = enterEdge->getSourceBlock();
        JITDUMP("Entry edge " FMT_BB " -> " FMT_BB " becomes " FMT_BB " -> " FMT_BB "\n", enterBlock->bbNum,
                header->bbNum, enterBlock->bbNum, preheader->bbNum);

        fgReplaceJumpTarget(enterBlock, preheader, header);
    }

    optSetPreheaderWeight(loop, preheader);

    return true;
}

//-----------------------------------------------------------------------------
// optSetPreheaderWeight: Set the weight of a newly created preheader, after it
// has been added to the flowgraph.
//
// Parameters:
//   loop      - The loop
//   preheader - The new preheader block
//
void Compiler::optSetPreheaderWeight(FlowGraphNaturalLoop* loop, BasicBlock* preheader)
{
    if (loop->EntryEdges().size() == 1)
    {
        // TODO-Quirk: If we have just one entry block then get the weight from there.
        // This doesn't really make sense for BBJ_COND, but it's what old loop
        // finding used to do.

        BasicBlock* prevEntering = loop->EntryEdge(0)->getSourceBlock();
        preheader->inheritWeight(prevEntering);
        preheader->RemoveFlags(BBF_PROF_WEIGHT);

        if (!fgIsUsingProfileWeights() || !prevEntering->KindIs(BBJ_COND))
        {
            return;
        }

        if ((prevEntering->bbWeight == BB_ZERO_WEIGHT) || (loop->GetHeader()->bbWeight == BB_ZERO_WEIGHT))
        {
            preheader->bbWeight = BB_ZERO_WEIGHT;
            preheader->SetFlags(BBF_RUN_RARELY);
            return;
        }

        // Allow for either the fall-through or branch to target entry.
        BasicBlock* skipLoopBlock;
        if (prevEntering->FalseTargetIs(preheader))
        {
            skipLoopBlock = prevEntering->GetTrueTarget();
        }
        else
        {
            skipLoopBlock = prevEntering->GetFalseTarget();
        }
        assert(skipLoopBlock != loop->GetHeader());

        bool allValidProfileWeights = (prevEntering->hasProfileWeight() && skipLoopBlock->hasProfileWeight() &&
                                       loop->GetHeader()->hasProfileWeight());

        if (!allValidProfileWeights)
        {
            return;
        }

        weight_t loopEnteredCount = 0;
        weight_t loopSkippedCount = 0;
        bool     useEdgeWeights   = fgHaveValidEdgeWeights;

        if (useEdgeWeights)
        {
            const FlowEdge* edgeToEntry    = fgGetPredForBlock(preheader, prevEntering);
            const FlowEdge* edgeToSkipLoop = fgGetPredForBlock(skipLoopBlock, prevEntering);
            assert(edgeToEntry != nullptr);
            assert(edgeToSkipLoop != nullptr);

            loopEnteredCount = (edgeToEntry->edgeWeightMin() + edgeToEntry->edgeWeightMax()) / 2.0;
            loopSkippedCount = (edgeToSkipLoop->edgeWeightMin() + edgeToSkipLoop->edgeWeightMax()) / 2.0;

            // Watch out for cases where edge weights were not properly maintained
            // so that it appears no profile flow enters the loop.
            //
            useEdgeWeights = !fgProfileWeightsConsistent(loopEnteredCount, BB_ZERO_WEIGHT);
        }

        if (!useEdgeWeights)
        {
            loopEnteredCount = loop->GetHeader()->bbWeight;
            loopSkippedCount = skipLoopBlock->bbWeight;
        }

        weight_t loopTakenRatio = loopEnteredCount / (loopEnteredCount + loopSkippedCount);

        JITDUMP("%s edge weights; loopEnterCount " FMT_WT " loopSkipCount " FMT_WT " taken ratio " FMT_WT "\n",
                fgHaveValidEdgeWeights ? (useEdgeWeights ? "valid" : "ignored") : "invalid", loopEnteredCount,
                loopSkippedCount, loopTakenRatio);

        // Calculate a good approximation of the preheader's block weight
        weight_t preheaderWeight = (prevEntering->bbWeight * loopTakenRatio);
        preheader->setBBProfileWeight(preheaderWeight);
        assert(!preheader->isRunRarely());

        // Normalize edge weights
        FlowEdge* const edgeToPreheader = fgGetPredForBlock(preheader, prevEntering);
        assert(edgeToPreheader != nullptr);
        edgeToPreheader->setEdgeWeights(preheader->bbWeight, preheader->bbWeight, preheader);

        FlowEdge* const edgeFromPreheader = fgGetPredForBlock(loop->GetHeader(), preheader);
        edgeFromPreheader->setEdgeWeights(preheader->bbWeight, preheader->bbWeight, loop->GetHeader());
        return;
    }
}

/*****************************************************************************
 *
 *  See if the given tree can be computed in the given precision (which must
 *  be smaller than the type of the tree for this to make sense). If 'doit'
 *  is false, we merely check to see whether narrowing is possible; if we
 *  get called with 'doit' being true, we actually perform the narrowing.
 */

bool Compiler::optNarrowTree(GenTree* tree, var_types srct, var_types dstt, ValueNumPair vnpNarrow, bool doit)
{
    genTreeOps oper;
    unsigned   kind;

    noway_assert(tree);
    noway_assert(genActualType(tree->gtType) == genActualType(srct));

    /* Assume we're only handling integer types */
    noway_assert(varTypeIsIntegral(srct));
    noway_assert(varTypeIsIntegral(dstt));

    unsigned srcSize = genTypeSize(srct);
    unsigned dstSize = genTypeSize(dstt);

    /* dstt must be smaller than srct to narrow */
    if (dstSize >= srcSize)
    {
        return false;
    }

    /* Figure out what kind of a node we have */
    oper = tree->OperGet();
    kind = tree->OperKind();

    ValueNumPair NoVNPair = ValueNumPair();

    if (kind & GTK_LEAF)
    {
        switch (oper)
        {
            /* Constants can usually be narrowed by changing their value */
            CLANG_FORMAT_COMMENT_ANCHOR;

#ifndef TARGET_64BIT
            __int64 lval;
            __int64 lmask;

            case GT_CNS_LNG:
                lval  = tree->AsIntConCommon()->LngValue();
                lmask = 0;

                switch (dstt)
                {
                    case TYP_BYTE:
                        lmask = 0x0000007F;
                        break;
                    case TYP_UBYTE:
                        lmask = 0x000000FF;
                        break;
                    case TYP_SHORT:
                        lmask = 0x00007FFF;
                        break;
                    case TYP_USHORT:
                        lmask = 0x0000FFFF;
                        break;
                    case TYP_INT:
                        lmask = 0x7FFFFFFF;
                        break;
                    case TYP_UINT:
                        lmask = 0xFFFFFFFF;
                        break;

                    default:
                        return false;
                }

                if ((lval & lmask) != lval)
                    return false;

                if (doit)
                {
                    tree->BashToConst(static_cast<int32_t>(lval));
                    if (vnStore != nullptr)
                    {
                        fgValueNumberTreeConst(tree);
                    }
                }

                return true;
#endif

            case GT_CNS_INT:

                ssize_t ival;
                ival = tree->AsIntCon()->gtIconVal;
                ssize_t imask;
                imask = 0;

                switch (dstt)
                {
                    case TYP_BYTE:
                        imask = 0x0000007F;
                        break;
                    case TYP_UBYTE:
                        imask = 0x000000FF;
                        break;
                    case TYP_SHORT:
                        imask = 0x00007FFF;
                        break;
                    case TYP_USHORT:
                        imask = 0x0000FFFF;
                        break;
#ifdef TARGET_64BIT
                    case TYP_INT:
                        imask = 0x7FFFFFFF;
                        break;
                    case TYP_UINT:
                        imask = 0xFFFFFFFF;
                        break;
#endif // TARGET_64BIT
                    default:
                        return false;
                }

                if ((ival & imask) != ival)
                {
                    return false;
                }

#ifdef TARGET_64BIT
                if (doit)
                {
                    tree->gtType                = TYP_INT;
                    tree->AsIntCon()->gtIconVal = (int)ival;
                    if (vnStore != nullptr)
                    {
                        fgValueNumberTreeConst(tree);
                    }
                }
#endif // TARGET_64BIT

                return true;

            /* Operands that are in memory can usually be narrowed
               simply by changing their gtType */

            case GT_LCL_VAR:
                /* We only allow narrowing long -> int for a GT_LCL_VAR */
                if (dstSize == sizeof(int))
                {
                    goto NARROW_IND;
                }
                break;

            case GT_LCL_FLD:
                goto NARROW_IND;
            default:
                break;
        }

        noway_assert(doit == false);
        return false;
    }

    if (kind & (GTK_BINOP | GTK_UNOP))
    {
        GenTree* op1;
        op1 = tree->AsOp()->gtOp1;
        GenTree* op2;
        op2 = tree->AsOp()->gtOp2;

        switch (tree->gtOper)
        {
            case GT_AND:
                noway_assert(genActualType(tree->gtType) == genActualType(op1->gtType));
                noway_assert(genActualType(tree->gtType) == genActualType(op2->gtType));

                GenTree* opToNarrow;
                opToNarrow = nullptr;
                GenTree** otherOpPtr;
                otherOpPtr = nullptr;
                bool foundOperandThatBlocksNarrowing;
                foundOperandThatBlocksNarrowing = false;

                // If 'dstt' is unsigned and one of the operands can be narrowed into 'dsst',
                // the result of the GT_AND will also fit into 'dstt' and can be narrowed.
                // The same is true if one of the operands is an int const and can be narrowed into 'dsst'.
                if (!gtIsActiveCSE_Candidate(op2) && ((op2->gtOper == GT_CNS_INT) || varTypeIsUnsigned(dstt)))
                {
                    if (optNarrowTree(op2, srct, dstt, NoVNPair, false))
                    {
                        opToNarrow = op2;
                        otherOpPtr = &tree->AsOp()->gtOp1;
                    }
                    else
                    {
                        foundOperandThatBlocksNarrowing = true;
                    }
                }

                if ((opToNarrow == nullptr) && !gtIsActiveCSE_Candidate(op1) &&
                    ((op1->gtOper == GT_CNS_INT) || varTypeIsUnsigned(dstt)))
                {
                    if (optNarrowTree(op1, srct, dstt, NoVNPair, false))
                    {
                        opToNarrow = op1;
                        otherOpPtr = &tree->AsOp()->gtOp2;
                    }
                    else
                    {
                        foundOperandThatBlocksNarrowing = true;
                    }
                }

                if (opToNarrow != nullptr)
                {
                    // We will change the type of the tree and narrow opToNarrow
                    //
                    if (doit)
                    {
                        tree->gtType = genActualType(dstt);
                        tree->SetVNs(vnpNarrow);

                        optNarrowTree(opToNarrow, srct, dstt, NoVNPair, true);
                        // We may also need to cast away the upper bits of *otherOpPtr
                        if (srcSize == 8)
                        {
                            assert(tree->gtType == TYP_INT);
                            GenTree* castOp = gtNewCastNode(TYP_INT, *otherOpPtr, false, TYP_INT);
#ifdef DEBUG
                            castOp->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED;
#endif
                            *otherOpPtr = castOp;
                        }
                    }
                    return true;
                }

                if (foundOperandThatBlocksNarrowing)
                {
                    noway_assert(doit == false);
                    return false;
                }

                goto COMMON_BINOP;

            case GT_ADD:
            case GT_MUL:

                if (tree->gtOverflow() || varTypeIsSmall(dstt))
                {
                    noway_assert(doit == false);
                    return false;
                }
                FALLTHROUGH;

            case GT_OR:
            case GT_XOR:
                noway_assert(genActualType(tree->gtType) == genActualType(op1->gtType));
                noway_assert(genActualType(tree->gtType) == genActualType(op2->gtType));
            COMMON_BINOP:
                if (gtIsActiveCSE_Candidate(op1) || gtIsActiveCSE_Candidate(op2) ||
                    !optNarrowTree(op1, srct, dstt, NoVNPair, doit) || !optNarrowTree(op2, srct, dstt, NoVNPair, doit))
                {
                    noway_assert(doit == false);
                    return false;
                }

                /* Simply change the type of the tree */

                if (doit)
                {
                    if (tree->gtOper == GT_MUL && (tree->gtFlags & GTF_MUL_64RSLT))
                    {
                        tree->gtFlags &= ~GTF_MUL_64RSLT;
                    }

                    tree->gtType = genActualType(dstt);
                    tree->SetVNs(vnpNarrow);
                }

                return true;

            case GT_IND:

            NARROW_IND:

                if ((dstSize > genTypeSize(tree->gtType)) &&
                    (varTypeIsUnsigned(dstt) && !varTypeIsUnsigned(tree->gtType)))
                {
                    return false;
                }

                /* Simply change the type of the tree */

                if (doit && (dstSize <= genTypeSize(tree->gtType)))
                {
                    if (!varTypeIsSmall(dstt))
                    {
                        dstt = varTypeToSigned(dstt);
                    }

                    tree->gtType = dstt;
                    tree->SetVNs(vnpNarrow);
                }

                return true;

            case GT_EQ:
            case GT_NE:
            case GT_LT:
            case GT_LE:
            case GT_GT:
            case GT_GE:

                /* These can always be narrowed since they only represent 0 or 1 */
                return true;

            case GT_CAST:
            {
#ifdef DEBUG
                if ((tree->gtDebugFlags & GTF_DEBUG_CAST_DONT_FOLD) != 0)
                {
                    return false;
                }
#endif

                if ((tree->CastToType() != srct) || tree->gtOverflow())
                {
                    return false;
                }

                if (varTypeIsInt(op1) && varTypeIsInt(dstt) && tree->TypeIs(TYP_LONG))
                {
                    // We have a CAST that converts into to long while dstt is int.
                    // so we can just convert the cast to int -> int and someone will clean it up.
                    if (doit)
                    {
                        tree->CastToType() = TYP_INT;
                        tree->ChangeType(TYP_INT);
                        tree->ClearUnsigned();
                    }
                    return true;
                }
            }
                return false;

            case GT_COMMA:
                if (!gtIsActiveCSE_Candidate(op2) && optNarrowTree(op2, srct, dstt, vnpNarrow, doit))
                {
                    /* Simply change the type of the tree */

                    if (doit)
                    {
                        tree->gtType = genActualType(dstt);
                        tree->SetVNs(vnpNarrow);
                    }
                    return true;
                }
                return false;

            default:
                noway_assert(doit == false);
                return false;
        }
    }

    return false;
}

//------------------------------------------------------------------------
// optRecordSsaUses: note any SSA uses within tree
//
// Arguments:
//   tree     - tree to examine
//   block    - block that does (or will) contain tree
//
// Notes:
//   Ignores SSA defs. We assume optimizations that modify trees with
//   SSA defs are introducing new defs for locals that do not require PHIs
//   or updating existing defs in place.
//
//   Currently does not examine PHI_ARG nodes as no opt phases introduce new PHIs.
//
//   Assumes block is a block that was rewritten by SSA or introduced post-SSA
//   (in particular, block is not unreachable).
//
void Compiler::optRecordSsaUses(GenTree* tree, BasicBlock* block)
{
    class SsaRecordingVisitor : public GenTreeVisitor<SsaRecordingVisitor>
    {
    private:
        BasicBlock* const m_block;

    public:
        enum
        {
            DoPreOrder    = true,
            DoLclVarsOnly = true
        };

        SsaRecordingVisitor(Compiler* compiler, BasicBlock* block)
            : GenTreeVisitor<SsaRecordingVisitor>(compiler), m_block(block)
        {
        }

        Compiler::fgWalkResult PreOrderVisit(GenTree** use, GenTree* user)
        {
            GenTreeLclVarCommon* const tree  = (*use)->AsLclVarCommon();
            const bool                 isUse = (tree->gtFlags & GTF_VAR_DEF) == 0;

            if (isUse)
            {
                if (tree->HasSsaName())
                {
                    unsigned const      lclNum    = tree->GetLclNum();
                    unsigned const      ssaNum    = tree->GetSsaNum();
                    LclVarDsc* const    varDsc    = m_compiler->lvaGetDesc(lclNum);
                    LclSsaVarDsc* const ssaVarDsc = varDsc->GetPerSsaData(ssaNum);
                    ssaVarDsc->AddUse(m_block);
                }
                else
                {
                    assert(!m_compiler->lvaInSsa(tree->GetLclNum()));
                    assert(!tree->HasCompositeSsaName());
                }
            }

            return fgWalkResult::WALK_CONTINUE;
        }
    };

    SsaRecordingVisitor srv(this, block);
    srv.WalkTree(&tree, nullptr);
}

//------------------------------------------------------------------------
// optPerformHoistExpr: hoist an expression into the preheader of a loop
//
// Arguments:
//   origExpr - tree to hoist
//   exprBb   - block containing the tree
//   loop     - loop that we're hoisting origExpr out of
//
void Compiler::optPerformHoistExpr(GenTree* origExpr, BasicBlock* exprBb, FlowGraphNaturalLoop* loop)
{
    assert(exprBb != nullptr);
    assert(loop->EntryEdges().size() == 1);

    BasicBlock* preheader = loop->EntryEdge(0)->getSourceBlock();
#ifdef DEBUG
    if (verbose)
    {
        printf("\nHoisting a copy of ");
        printTreeID(origExpr);
        printf(" " FMT_VN, origExpr->gtVNPair.GetLiberal());
        printf(" from " FMT_BB " into PreHeader " FMT_BB " for loop " FMT_LP " (head: " FMT_BB "):\n", exprBb->bbNum,
               preheader->bbNum, loop->GetIndex(), loop->GetHeader()->bbNum);
        gtDispTree(origExpr);
        printf("\n");
    }
#endif

    // Create a copy of the expression and mark it for CSE's.
    GenTree* hoistExpr = gtCloneExpr(origExpr);

    // The hoist Expr does not have to computed into a specific register,
    // so clear the RegNum if it was set in the original expression
    hoistExpr->ClearRegNum();

    // Copy any loop memory dependence.
    optCopyLoopMemoryDependence(origExpr, hoistExpr);

    // At this point we should have a cloned expression
    hoistExpr->gtFlags |= GTF_MAKE_CSE;
    assert(hoistExpr != origExpr);

    // The value of the expression isn't used.
    GenTree* hoist = gtUnusedValNode(hoistExpr);

    // Scan the tree for any new SSA uses.
    //
    optRecordSsaUses(hoist, preheader);

    preheader->CopyFlags(exprBb, BBF_COPY_PROPAGATE);

    Statement* hoistStmt = gtNewStmt(hoist);

    // Simply append the statement at the end of the preHead's list.
    Statement* firstStmt = preheader->firstStmt();
    if (firstStmt != nullptr)
    {
        /* append after last statement */

        Statement* lastStmt = preheader->lastStmt();
        assert(lastStmt->GetNextStmt() == nullptr);

        lastStmt->SetNextStmt(hoistStmt);
        hoistStmt->SetPrevStmt(lastStmt);
        firstStmt->SetPrevStmt(hoistStmt);
    }
    else
    {
        /* Empty pre-header - store the single statement in the block */

        preheader->bbStmtList = hoistStmt;
        hoistStmt->SetPrevStmt(hoistStmt);
    }

    hoistStmt->SetNextStmt(nullptr);

#ifdef DEBUG
    if (verbose)
    {
        printf("This hoisted copy placed in PreHeader (" FMT_BB "):\n", preheader->bbNum);
        gtDispTree(hoist);
        printf("\n");
    }
#endif

    if (fgNodeThreading == NodeThreading::AllTrees)
    {
        gtSetStmtInfo(hoistStmt);
        fgSetStmtSeq(hoistStmt);
    }

#ifdef DEBUG
    if (m_nodeTestData != nullptr)
    {

        // What is the depth of the loop "lnum"?
        ssize_t depth = loop->GetDepth();

        NodeToTestDataMap* testData = GetNodeTestData();

        TestLabelAndNum tlAndN;
        if (testData->Lookup(origExpr, &tlAndN) && tlAndN.m_tl == TL_LoopHoist)
        {
            if (tlAndN.m_num == -1)
            {
                printf("Node ");
                printTreeID(origExpr);
                printf(" was declared 'do not hoist', but is being hoisted.\n");
                assert(false);
            }
            else if (tlAndN.m_num != depth)
            {
                printf("Node ");
                printTreeID(origExpr);
                printf(" was declared as hoistable from loop at nesting depth %d; actually hoisted from loop at depth "
                       "%d.\n",
                       tlAndN.m_num, depth);
                assert(false);
            }
            else
            {
                // We've correctly hoisted this, so remove the annotation.  Later, we'll check for any remaining "must
                // hoist" annotations.
                testData->Remove(origExpr);
                // Now we insert an annotation to make sure that "hoistExpr" is actually CSE'd.
                tlAndN.m_tl  = TL_CSE_Def;
                tlAndN.m_num = m_loopHoistCSEClass++;
                testData->Set(hoistExpr, tlAndN);
            }
        }
    }
#endif

#if LOOP_HOIST_STATS
    if (!m_curLoopHasHoistedExpression)
    {
        m_loopsWithHoistedExpressions++;
        m_curLoopHasHoistedExpression = true;
    }
    m_totalHoistedExpressions++;
#endif // LOOP_HOIST_STATS
}

//------------------------------------------------------------------------
// optHoistLoopCode: run loop hoisting phase
//
// Returns:
//    suitable phase status
//
PhaseStatus Compiler::optHoistLoopCode()
{
    // If we don't have any loops in the method then take an early out now.
    if (m_loops->NumLoops() == 0)
    {
        JITDUMP("\nNo loops; no hoisting\n");
        return PhaseStatus::MODIFIED_NOTHING;
    }

#ifdef DEBUG
    unsigned jitNoHoist = JitConfig.JitNoHoist();
    if (jitNoHoist > 0)
    {
        JITDUMP("\nJitNoHoist set; no hoisting\n");
        return PhaseStatus::MODIFIED_NOTHING;
    }
#endif

#if 0
    // The code in this #if has been useful in debugging loop hoisting issues, by
    // enabling selective enablement of the loop hoisting optimization according to
    // method hash.
#ifdef DEBUG
    unsigned methHash = info.compMethodHash();
    char* lostr = getenv("loophoisthashlo");
    unsigned methHashLo = 0;
    if (lostr != NULL)
    {
        sscanf_s(lostr, "%x", &methHashLo);
        // methHashLo = (unsigned(atoi(lostr)) << 2);  // So we don't have to use negative numbers.
    }
    char* histr = getenv("loophoisthashhi");
    unsigned methHashHi = UINT32_MAX;
    if (histr != NULL)
    {
        sscanf_s(histr, "%x", &methHashHi);
        // methHashHi = (unsigned(atoi(histr)) << 2);  // So we don't have to use negative numbers.
    }
    if (methHash < methHashLo || methHash > methHashHi)
    {
        return PhaseStatus::MODIFIED_NOTHING;
    }
    printf("Doing loop hoisting in %s (0x%x).\n", info.compFullName, methHash);
#endif // DEBUG
#endif // 0     -- debugging loop hoisting issues

#ifdef DEBUG
    if (verbose)
    {
        printf("\n*************** In optHoistLoopCode()\n");
        fgDispHandlerTab();
    }
#endif

    optComputeInterestingVarSets();

    // Consider all the loops, visiting child loops first.
    //
    bool             modified = false;
    LoopHoistContext hoistCtxt(this);
    for (FlowGraphNaturalLoop* loop : m_loops->InPostOrder())
    {
#if LOOP_HOIST_STATS
        // Record stats
        m_curLoopHasHoistedExpression = false;
        m_loopsConsidered++;
#endif // LOOP_HOIST_STATS

        modified |= optHoistThisLoop(loop, &hoistCtxt);
    }

#ifdef DEBUG
    // Test Data stuff..
    //
    if (m_nodeTestData != nullptr)
    {
        NodeToTestDataMap* testData = GetNodeTestData();
        for (GenTree* const node : NodeToTestDataMap::KeyIteration(testData))
        {
            TestLabelAndNum tlAndN;
            bool            b = testData->Lookup(node, &tlAndN);
            assert(b);
            if (tlAndN.m_tl != TL_LoopHoist)
            {
                continue;
            }
            // Otherwise, it is a loop hoist annotation.
            assert(tlAndN.m_num < 100); // >= 100 indicates nested static field address, should already have been moved.
            if (tlAndN.m_num >= 0)
            {
                printf("Node ");
                printTreeID(node);
                printf(" was declared 'must hoist', but has not been hoisted.\n");
                assert(false);
            }
        }
    }
#endif // DEBUG

    return modified ? PhaseStatus::MODIFIED_EVERYTHING : PhaseStatus::MODIFIED_NOTHING;
}

//------------------------------------------------------------------------
// optHoistThisLoop: run loop hoisting for the indicated loop
//
// Arguments:
//    loop - loop to process
//    hoistCtxt - context for the hoisting
//
// Returns:
//    true if any hoisting was done
//
bool Compiler::optHoistThisLoop(FlowGraphNaturalLoop* loop, LoopHoistContext* hoistCtxt)
{
    // Ensure the per-loop sets/tables are empty.
    hoistCtxt->m_curLoopVnInvariantCache.RemoveAll();

    const LoopSideEffects& sideEffs = m_loopSideEffects[loop->GetIndex()];

#ifdef DEBUG
    if (verbose)
    {
        printf("optHoistThisLoop processing ");
        FlowGraphNaturalLoop::Dump(loop);
        printf("  Loop body %s a call\n", sideEffs.ContainsCall ? "contains" : "does not contain");
    }
#endif

    VARSET_TP loopVars(VarSetOps::Intersection(this, sideEffs.VarInOut, sideEffs.VarUseDef));

    hoistCtxt->m_loopVarInOutCount = VarSetOps::Count(this, sideEffs.VarInOut);
    hoistCtxt->m_loopVarCount      = VarSetOps::Count(this, loopVars);
    hoistCtxt->m_hoistedExprCount  = 0;

#ifndef TARGET_64BIT

    if (!VarSetOps::IsEmpty(this, lvaLongVars))
    {
        // Since 64-bit variables take up two registers on 32-bit targets, we increase
        //  the Counts such that each TYP_LONG variable counts twice.
        //
        VARSET_TP loopLongVars(VarSetOps::Intersection(this, loopVars, lvaLongVars));
        VARSET_TP inOutLongVars(VarSetOps::Intersection(this, sideEffs.VarInOut, lvaLongVars));

#ifdef DEBUG
        if (verbose)
        {
            printf("\n  LONGVARS(%d)=", VarSetOps::Count(this, lvaLongVars));
            dumpConvertedVarSet(this, lvaLongVars);
        }
#endif
        hoistCtxt->m_loopVarCount += VarSetOps::Count(this, loopLongVars);
        hoistCtxt->m_loopVarInOutCount += VarSetOps::Count(this, inOutLongVars);
    }
#endif // !TARGET_64BIT

#ifdef DEBUG
    if (verbose)
    {
        printf("\n  USEDEF  (%d)=", VarSetOps::Count(this, sideEffs.VarUseDef));
        dumpConvertedVarSet(this, sideEffs.VarUseDef);

        printf("\n  INOUT   (%d)=", hoistCtxt->m_loopVarInOutCount);
        dumpConvertedVarSet(this, sideEffs.VarInOut);

        printf("\n  LOOPVARS(%d)=", hoistCtxt->m_loopVarCount);
        dumpConvertedVarSet(this, loopVars);
        printf("\n");
    }
#endif

    if (!VarSetOps::IsEmpty(this, lvaFloatVars))
    {
        VARSET_TP loopFPVars(VarSetOps::Intersection(this, loopVars, lvaFloatVars));
        VARSET_TP inOutFPVars(VarSetOps::Intersection(this, sideEffs.VarInOut, lvaFloatVars));

        hoistCtxt->m_loopVarFPCount      = VarSetOps::Count(this, loopFPVars);
        hoistCtxt->m_loopVarInOutFPCount = VarSetOps::Count(this, inOutFPVars);
        hoistCtxt->m_hoistedFPExprCount  = 0;
        hoistCtxt->m_loopVarCount -= hoistCtxt->m_loopVarFPCount;
        hoistCtxt->m_loopVarInOutCount -= hoistCtxt->m_loopVarInOutFPCount;

#ifdef DEBUG
        if (verbose)
        {
            printf("  INOUT-FP(%d)=", hoistCtxt->m_loopVarInOutFPCount);
            dumpConvertedVarSet(this, inOutFPVars);

            printf("\n  LOOPV-FP(%d)=", hoistCtxt->m_loopVarFPCount);
            dumpConvertedVarSet(this, loopFPVars);

            printf("\n");
        }
#endif
    }
    else // lvaFloatVars is empty
    {
        hoistCtxt->m_loopVarFPCount      = 0;
        hoistCtxt->m_loopVarInOutFPCount = 0;
        hoistCtxt->m_hoistedFPExprCount  = 0;
    }

#ifdef TARGET_XARCH
    if (!VarSetOps::IsEmpty(this, lvaMaskVars))
    {
        VARSET_TP loopMskVars(VarSetOps::Intersection(this, loopVars, lvaMaskVars));
        VARSET_TP inOutMskVars(VarSetOps::Intersection(this, sideEffs.VarInOut, lvaMaskVars));

        hoistCtxt->m_loopVarMskCount      = VarSetOps::Count(this, loopMskVars);
        hoistCtxt->m_loopVarInOutMskCount = VarSetOps::Count(this, inOutMskVars);
        hoistCtxt->m_hoistedMskExprCount  = 0;
        hoistCtxt->m_loopVarCount -= hoistCtxt->m_loopVarMskCount;
        hoistCtxt->m_loopVarInOutCount -= hoistCtxt->m_loopVarInOutMskCount;

#ifdef DEBUG
        if (verbose)
        {
            printf("  INOUT-MSK(%d)=", hoistCtxt->m_loopVarInOutMskCount);
            dumpConvertedVarSet(this, inOutMskVars);

            printf("\n  LOOPV-MSK(%d)=", hoistCtxt->m_loopVarMskCount);
            dumpConvertedVarSet(this, loopMskVars);

            printf("\n");
        }
#endif
    }
    else // lvaMaskVars is empty
    {
        hoistCtxt->m_loopVarMskCount      = 0;
        hoistCtxt->m_loopVarInOutMskCount = 0;
        hoistCtxt->m_hoistedMskExprCount  = 0;
    }
#endif // TARGET_XARCH

    // Find the set of definitely-executed blocks.
    // Ideally, the definitely-executed blocks are the ones that post-dominate the entry block.
    // Until we have post-dominators, we'll special-case for single-exit blocks.
    //
    // Todo: it is not clear if this is a correctness requirement or a profitability heuristic.
    // It seems like the latter. Ideally there are enough safeguards to prevent hoisting exception
    // or side-effect dependent things. Note that HoistVisitor uses `m_beforeSideEffect` to determine if it's
    // ok to hoist a side-effect. It allows this only for the first block (the entry block), before any
    // side-effect has been seen. After the first block, it assumes that there has been a side effect and
    // no further side-effect can be hoisted. It is true that we don't analyze any program behavior in the
    // flow graph between the entry block and the subsequent blocks, whether they be the next block dominating
    // the exit block, or the pre-headers of nested loops.
    //
    // We really should consider hoisting from conditionally executed blocks, if they are frequently executed
    // and it is safe to evaluate the tree early.
    //
    ArrayStack<BasicBlock*> defExec(getAllocatorLoopHoist());

    // Add the pre-headers of any child loops to the list of blocks to consider for hoisting.
    // Note that these are not necessarily definitely executed. However, it is a heuristic that they will
    // often provide good opportunities for further hoisting since we hoist from inside-out,
    // and the inner loop may have already hoisted something loop-invariant to them. If the child
    // loop pre-header block would be added anyway (by dominating the loop exit block), we don't
    // add it here, and let it be added naturally, below.
    //
    // Note that all pre-headers get added first, which means they get considered for hoisting last. It is
    // assumed that the order does not matter for correctness.
    // Note that the order does matter for the hoisting profitability heuristics, as we might
    // run out of hoisting budget when processing the blocks.
    //
    // For example, consider this loop nest:
    //
    // for (....) { // loop L00
    //    pre-header 1
    //    for (...) { // loop L01
    //    }
    //    // pre-header 2
    //    for (...) { // loop L02
    //       // pre-header 3
    //       for (...) { // loop L03
    //       }
    //    }
    // }
    //
    // The order in the siblink links is RPO, so the loop below will push pre-header 1, then pre-header 2.
    // Then we will push the loop exit block, any IDom tree blocks leading to the header block, and finally
    // the header block itself. optHoistLoopBlocks performs hoisting in reverse, so we will hoist the header
    // block first and the pre-headers last.
    //
    // Note that pre-header 3 is not pushed, since it is not a direct child. It would have been processed
    // when loop L02 was considered for hoisting.

    for (FlowGraphNaturalLoop* childLoop = loop->GetChild(); childLoop != nullptr; childLoop = childLoop->GetSibling())
    {
        assert(childLoop->EntryEdges().size() == 1);
        BasicBlock* childPreHead = childLoop->EntryEdge(0)->getSourceBlock();
        if (loop->ExitEdges().size() == 1)
        {
            if (m_domTree->Dominates(childPreHead, loop->ExitEdges()[0]->getSourceBlock()))
            {
                // If the child loop pre-header dominates the exit, it will get added in the dominator tree
                // loop below.
                continue;
            }
        }
        else
        {
            // If the child loop pre-header is the loop entry for a multi-exit loop, it will get added below.
            if (childPreHead == loop->GetHeader())
            {
                continue;
            }
        }
        JITDUMP("  --  " FMT_BB " (child loop pre-header)\n", childPreHead->bbNum);
        defExec.Push(childPreHead);
    }

    if (loop->ExitEdges().size() == 1)
    {
        BasicBlock* exiting = loop->ExitEdges()[0]->getSourceBlock();
        JITDUMP("  Considering hoisting in blocks that either dominate exit block " FMT_BB
                ", or pre-headers of nested loops, if any:\n",
                exiting->bbNum);

        // Push dominators, until we reach the header or exit the loop.
        //
        // Note that there is a mismatch between the dominator tree dominance
        // and loop header dominance; the dominator tree dominance relation
        // guarantees that a block A that dominates B was exited before B is
        // entered, meaning it could not possibly have thrown an exception. On
        // the other hand loop finding guarantees only that the header was
        // entered before other blocks in the loop. If the header is a
        // try-begin then blocks inside the catch may not necessarily be fully
        // dominated by the header, but may still be part of the loop.
        //
        BasicBlock* cur = exiting;
        while ((cur != nullptr) && (cur != loop->GetHeader()) && loop->ContainsBlock(cur))
        {
            JITDUMP("  --  " FMT_BB " (dominate exit block)\n", cur->bbNum);
            defExec.Push(cur);
            cur = cur->bbIDom;
        }

        assert((cur == loop->GetHeader()) || bbIsTryBeg(loop->GetHeader()));
    }
    else // More than one exit
    {
        // We'll assume that only the entry block is definitely executed.
        // We could in the future do better.

        JITDUMP("  Considering hoisting in entry block " FMT_BB " because " FMT_LP " has more than one exit\n",
                loop->GetHeader()->bbNum, loop->GetIndex());
    }

    JITDUMP("  --  " FMT_BB " (header block)\n", loop->GetHeader()->bbNum);
    defExec.Push(loop->GetHeader());

    optHoistLoopBlocks(loop, &defExec, hoistCtxt);

    unsigned numHoisted = hoistCtxt->m_hoistedFPExprCount + hoistCtxt->m_hoistedExprCount;
#ifdef TARGET_XARCH
    numHoisted += hoistCtxt->m_hoistedMskExprCount;
#endif // TARGET_XARCH
    return numHoisted > 0;
}

bool Compiler::optIsProfitableToHoistTree(GenTree* tree, FlowGraphNaturalLoop* loop, LoopHoistContext* hoistCtxt)
{
    bool loopContainsCall = m_loopSideEffects[loop->GetIndex()].ContainsCall;

    int availRegCount;
    int hoistedExprCount;
    int loopVarCount;
    int varInOutCount;

    if (varTypeUsesIntReg(tree))
    {
        hoistedExprCount = hoistCtxt->m_hoistedExprCount;
        loopVarCount     = hoistCtxt->m_loopVarCount;
        varInOutCount    = hoistCtxt->m_loopVarInOutCount;

        availRegCount = CNT_CALLEE_SAVED - 1;
        if (!loopContainsCall)
        {
            availRegCount += CNT_CALLEE_TRASH - 1;
        }
#ifndef TARGET_64BIT
        // For our 32-bit targets Long types take two registers.
        if (varTypeIsLong(tree->TypeGet()))
        {
            availRegCount = (availRegCount + 1) / 2;
        }
#endif
    }
#ifdef TARGET_XARCH
    else if (varTypeUsesMaskReg(tree))
    {
        hoistedExprCount = hoistCtxt->m_hoistedMskExprCount;
        loopVarCount     = hoistCtxt->m_loopVarMskCount;
        varInOutCount    = hoistCtxt->m_loopVarInOutMskCount;

        availRegCount = CNT_CALLEE_SAVED_MASK;
        if (!loopContainsCall)
        {
            availRegCount += CNT_CALLEE_TRASH_MASK - 1;
        }
    }
#endif // TARGET_XARCH
    else
    {
        assert(varTypeUsesFloatReg(tree));

        hoistedExprCount = hoistCtxt->m_hoistedFPExprCount;
        loopVarCount     = hoistCtxt->m_loopVarFPCount;
        varInOutCount    = hoistCtxt->m_loopVarInOutFPCount;

        availRegCount = CNT_CALLEE_SAVED_FLOAT;
        if (!loopContainsCall)
        {
            availRegCount += CNT_CALLEE_TRASH_FLOAT - 1;
        }
#ifdef TARGET_ARM
        // For ARM each double takes two FP registers
        // For now on ARM we won't track singles/doubles
        // and instead just assume that we always have doubles.
        //
        availRegCount /= 2;
#endif
    }

    // decrement the availRegCount by the count of expression that we have already hoisted.
    availRegCount -= hoistedExprCount;

    // the variables that are read/written inside the loop should
    // always be a subset of the InOut variables for the loop
    assert(loopVarCount <= varInOutCount);

    // When loopVarCount >= availRegCount we believe that all of the
    // available registers will get used to hold LclVars inside the loop.
    // This pessimistically assumes that each loopVar has a conflicting
    // lifetime with every other loopVar.
    // For this case we will hoist the expression only if is profitable
    // to place it in a stack home location (GetCostEx() >= 2*IND_COST_EX)
    // as we believe it will be placed in the stack or one of the other
    // loopVars will be spilled into the stack
    //
    if (loopVarCount >= availRegCount)
    {
        // Don't hoist expressions that are not heavy: tree->GetCostEx() < (2*IND_COST_EX)
        if (tree->GetCostEx() < (2 * IND_COST_EX))
        {
            JITDUMP("    tree cost too low: %d < %d (loopVarCount %u >= availRegCount %u)\n", tree->GetCostEx(),
                    2 * IND_COST_EX, loopVarCount, availRegCount);
            return false;
        }
    }

    // When varInOutCount < availRegCount we are know that there are
    // some available register(s) when we enter the loop body.
    // When varInOutCount == availRegCount there often will be a register
    // available when we enter the loop body, since a loop often defines a
    // LclVar on exit or there is often at least one LclVar that is worth
    // spilling to the stack to make way for this hoisted expression.
    // So we are willing hoist an expression with GetCostEx() == MIN_CSE_COST
    //
    if (varInOutCount > availRegCount)
    {
        // Don't hoist expressions that barely meet CSE cost requirements: tree->GetCostEx() == MIN_CSE_COST
        if (tree->GetCostEx() <= MIN_CSE_COST + 1)
        {
            JITDUMP("    tree not good CSE: %d <= %d (varInOutCount %u > availRegCount %u)\n", tree->GetCostEx(),
                    2 * MIN_CSE_COST + 1, varInOutCount, availRegCount)
            return false;
        }
    }

    return true;
}

//------------------------------------------------------------------------
// optRecordLoopMemoryDependence: record that tree's value number
//   is dependent on a particular memory VN
//
// Arguments:
//   tree -- tree in question
//   block -- block containing tree
//   memoryVN -- VN for a "map" from a select operation encounterd
//     while computing the tree's VN
//
// Notes:
//   Only tracks trees in loops, and memory updates in the same loop nest.
//   So this is a coarse-grained dependence that is only usable for
//   hoisting tree out of its enclosing loops.
//
void Compiler::optRecordLoopMemoryDependence(GenTree* tree, BasicBlock* block, ValueNum memoryVN)
{
    // Find the loop associated with this memory VN.
    //
    FlowGraphNaturalLoop* updateLoop = vnStore->LoopOfVN(memoryVN);

    if (updateLoop == nullptr)
    {
        // memoryVN defined outside of any loop, we can ignore.
        //
        JITDUMP("      ==> Not updating loop memory dependence of [%06u], memory " FMT_VN " not defined in a loop\n",
                dspTreeID(tree), memoryVN);
        return;
    }

    // If the update block is not the header of a loop containing
    // block, we can also ignore the update.
    //
    if (!updateLoop->ContainsBlock(block))
    {
#ifdef DEBUG
        FlowGraphNaturalLoop* blockLoop = m_blockToLoop->GetLoop(block);

        JITDUMP("      ==> Not updating loop memory dependence of [%06u]/" FMT_LP ", memory " FMT_VN "/" FMT_LP
                " is not defined in a contained block\n",
                dspTreeID(tree), blockLoop->GetIndex(), memoryVN, updateLoop->GetIndex());
#endif
        return;
    }

    // If we already have a recorded a loop entry block for this
    // tree, see if the new update is for a more closely nested
    // loop.
    //
    NodeToLoopMemoryBlockMap* const map      = GetNodeToLoopMemoryBlockMap();
    BasicBlock*                     mapBlock = nullptr;

    if (map->Lookup(tree, &mapBlock))
    {
        // If the update loop contains the existing map block,
        // the existing entry is more constraining. So no
        // update needed.
        //
        if (updateLoop->ContainsBlock(mapBlock))
        {
#ifdef DEBUG
            FlowGraphNaturalLoop* mapLoop = m_blockToLoop->GetLoop(mapBlock);

            JITDUMP("      ==> Not updating loop memory dependence of [%06u]; alrady constrained to " FMT_LP
                    " nested in " FMT_LP "\n",
                    dspTreeID(tree), mapLoop->GetIndex(), updateLoop->GetIndex());
#endif
            return;
        }
    }

    // MemoryVN now describes the most constraining loop memory dependence
    // we know of. Update the map.
    //
    JITDUMP("      ==> Updating loop memory dependence of [%06u] to " FMT_LP "\n", dspTreeID(tree),
            updateLoop->GetIndex());
    map->Set(tree, updateLoop->GetHeader(), NodeToLoopMemoryBlockMap::Overwrite);
}

//------------------------------------------------------------------------
// optCopyLoopMemoryDependence: record that tree's loop memory dependence
//   is the same as some other tree.
//
// Arguments:
//   fromTree -- tree to copy dependence from
//   toTree -- tree in question
//
void Compiler::optCopyLoopMemoryDependence(GenTree* fromTree, GenTree* toTree)
{
    NodeToLoopMemoryBlockMap* const map      = GetNodeToLoopMemoryBlockMap();
    BasicBlock*                     mapBlock = nullptr;

    if (map->Lookup(fromTree, &mapBlock))
    {
        map->Set(toTree, mapBlock);
    }
}

//------------------------------------------------------------------------
// AddVariableLiveness: Adds the variable liveness information for 'blk'
//
// Arguments:
//   comp - Compiler instance
//   blk  - Block whose liveness is to be added
//
void LoopSideEffects::AddVariableLiveness(Compiler* comp, BasicBlock* blk)
{
    VarSetOps::UnionD(comp, VarInOut, blk->bbLiveIn);
    VarSetOps::UnionD(comp, VarInOut, blk->bbLiveOut);

    VarSetOps::UnionD(comp, VarUseDef, blk->bbVarUse);
    VarSetOps::UnionD(comp, VarUseDef, blk->bbVarDef);
}

//------------------------------------------------------------------------
// AddModifiedField: Record that a field is modified in the loop.
//
// Arguments:
//   comp      - Compiler instance
//   fldHnd    - Field handle being modified
//   fieldKind - Kind of field
//
void LoopSideEffects::AddModifiedField(Compiler* comp, CORINFO_FIELD_HANDLE fldHnd, FieldKindForVN fieldKind)
{
    if (FieldsModified == nullptr)
    {
        FieldsModified = new (comp->getAllocatorLoopHoist()) FieldHandleSet(comp->getAllocatorLoopHoist());
    }
    FieldsModified->Set(fldHnd, fieldKind, FieldHandleSet::Overwrite);
}

//------------------------------------------------------------------------
// AddModifiedElemType: Record that an array with the specified element type is
// being modified.
//
// Arguments:
//   comp      - Compiler instance
//   structHnd - Handle for struct. Can also be an encoding of a primitive
//               handle, see {Encode/Decode}ElemType.
//
void LoopSideEffects::AddModifiedElemType(Compiler* comp, CORINFO_CLASS_HANDLE structHnd)
{
    if (ArrayElemTypesModified == nullptr)
    {
        ArrayElemTypesModified = new (comp->getAllocatorLoopHoist()) ClassHandleSet(comp->getAllocatorLoopHoist());
    }
    ArrayElemTypesModified->Set(structHnd, true, ClassHandleSet::Overwrite);
}

//------------------------------------------------------------------------
// optHoistLoopBlocks: Hoist invariant expression out of the loop.
//
// Arguments:
//    loop - The loop
//    blocks - A stack of blocks belonging to the loop
//    hoistContext - The loop hoist context
//
// Assumptions:
//    The `blocks` stack contains the definitely-executed blocks in
//    the loop, in the execution order, starting with the loop entry
//    block on top of the stack.
//
void Compiler::optHoistLoopBlocks(FlowGraphNaturalLoop*    loop,
                                  ArrayStack<BasicBlock*>* blocks,
                                  LoopHoistContext*        hoistContext)
{
    class HoistVisitor : public GenTreeVisitor<HoistVisitor>
    {
        class Value
        {
            GenTree* m_node;

        public:
            bool m_hoistable;
            bool m_cctorDependent;
            bool m_invariant;

#ifdef DEBUG
            const char* m_failReason;
#endif

            Value(GenTree* node) : m_node(node), m_hoistable(false), m_cctorDependent(false), m_invariant(false)
            {
#ifdef DEBUG
                m_failReason = "unset";
#endif
            }

            GenTree* Node()
            {
                return m_node;
            }
        };

        ArrayStack<Value>     m_valueStack;
        bool                  m_beforeSideEffect;
        FlowGraphNaturalLoop* m_loop;
        LoopHoistContext*     m_hoistContext;
        BasicBlock*           m_currentBlock;

        bool IsNodeHoistable(GenTree* node)
        {
            // TODO-CQ: This is a more restrictive version of a check that optIsCSEcandidate already does - it allows
            // a struct typed node if a class handle can be recovered from it.
            if (node->TypeGet() == TYP_STRUCT)
            {
                return false;
            }
            else if (node->OperIs(GT_NULLCHECK))
            {
                // If a null-check is for `this` object, it is safe to
                // hoist it out of the loop. Assertionprop will get rid
                // of left over nullchecks present inside the loop. Also,
                // since NULLCHECK has no value, it will never be CSE,
                // hence this check is not present in optIsCSEcandidate().
                return true;
            }

            // Tree must be a suitable CSE candidate for us to be able to hoist it.
            return m_compiler->optIsCSEcandidate(node);
        }

        bool IsTreeVNInvariant(GenTree* tree)
        {
            ValueNum vn = tree->gtVNPair.GetLiberal();
            bool     vnIsInvariant =
                m_compiler->optVNIsLoopInvariant(vn, m_loop, &m_hoistContext->m_curLoopVnInvariantCache);

            // Even though VN is invariant in the loop (say a constant) its value may depend on position
            // of tree, so for loop hoisting we must also check that any memory read by tree
            // is also invariant in the loop.
            //
            if (vnIsInvariant)
            {
                vnIsInvariant = IsTreeLoopMemoryInvariant(tree);
            }
            return vnIsInvariant;
        }

        bool IsHoistableOverExcepSibling(GenTree* node, bool siblingHasExcep)
        {
            JITDUMP("      [%06u]", dspTreeID(node));

            if ((node->gtFlags & GTF_ALL_EFFECT) != 0)
            {
                // If the hoistable node has any side effects, make sure
                // we don't hoist it past a sibling that throws any exception.
                if (siblingHasExcep)
                {
                    JITDUMP(" not hoistable: cannot move past node that throws exception.\n");
                    return false;
                }
            }
            JITDUMP(" hoistable\n");
            return true;
        }

        //------------------------------------------------------------------------
        // IsTreeLoopMemoryInvariant: determine if the value number of tree
        //   is dependent on the tree being executed within the current loop
        //
        // Arguments:
        //   tree -- tree in question
        //
        // Returns:
        //   true if tree could be evaluated just before loop and get the
        //   same value.
        //
        // Note:
        //   Calls are optimistically assumed to be invariant.
        //   Caller must do their own analysis for these tree types.
        //
        bool IsTreeLoopMemoryInvariant(GenTree* tree)
        {
            if (tree->IsCall())
            {
                // Calls are handled specially by hoisting, and loop memory dependence
                // must be checked by other means.
                //
                return true;
            }

            NodeToLoopMemoryBlockMap* const map            = m_compiler->GetNodeToLoopMemoryBlockMap();
            BasicBlock*                     loopEntryBlock = nullptr;
            if (map->Lookup(tree, &loopEntryBlock))
            {
                for (MemoryKind memoryKind : allMemoryKinds())
                {
                    ValueNum loopMemoryVN =
                        m_compiler->GetMemoryPerSsaData(loopEntryBlock->bbMemorySsaNumIn[memoryKind])
                            ->m_vnPair.GetLiberal();
                    if (!m_compiler->optVNIsLoopInvariant(loopMemoryVN, m_loop,
                                                          &m_hoistContext->m_curLoopVnInvariantCache))
                    {
                        return false;
                    }
                }
            }

            return true;
        }

    public:
        enum
        {
            ComputeStack      = false,
            DoPreOrder        = true,
            DoPostOrder       = true,
            DoLclVarsOnly     = false,
            UseExecutionOrder = true,
        };

        HoistVisitor(Compiler* compiler, FlowGraphNaturalLoop* loop, LoopHoistContext* hoistContext)
            : GenTreeVisitor(compiler)
            , m_valueStack(compiler->getAllocator(CMK_LoopHoist))
            , m_beforeSideEffect(true)
            , m_loop(loop)
            , m_hoistContext(hoistContext)
            , m_currentBlock(nullptr)
        {
        }

        void HoistBlock(BasicBlock* block)
        {
            m_currentBlock = block;
            for (Statement* const stmt : block->NonPhiStatements())
            {
                WalkTree(stmt->GetRootNodePointer(), nullptr);
                Value& top = m_valueStack.TopRef();
                assert(top.Node() == stmt->GetRootNode());

                // hoist the top node?
                if (top.m_hoistable)
                {
                    m_compiler->optHoistCandidate(stmt->GetRootNode(), block, m_loop, m_hoistContext);
                }
                else
                {
                    JITDUMP("      [%06u] %s: %s\n", dspTreeID(top.Node()),
                            top.m_invariant ? "not hoistable" : "not invariant", top.m_failReason);
                }

                m_valueStack.Reset();
            }

            // Only unconditionally executed blocks in the loop are visited (see optHoistThisLoop)
            // so after we're done visiting the first block we need to assume the worst, that the
            // blocks that are not visited have side effects.
            m_beforeSideEffect = false;
        }

        fgWalkResult PreOrderVisit(GenTree** use, GenTree* user)
        {
            GenTree* node = *use;
            JITDUMP("----- PreOrderVisit for [%06u] %s\n", dspTreeID(node), GenTree::OpName(node->OperGet()));
            m_valueStack.Emplace(node);
            return fgWalkResult::WALK_CONTINUE;
        }

        fgWalkResult PostOrderVisit(GenTree** use, GenTree* user)
        {
            GenTree* tree = *use;
            JITDUMP("----- PostOrderVisit for [%06u] %s\n", dspTreeID(tree), GenTree::OpName(tree->OperGet()));

            if (tree->OperIsLocalRead())
            {
                GenTreeLclVarCommon* lclVar = tree->AsLclVarCommon();
                unsigned             lclNum = lclVar->GetLclNum();

                // To be invariant the variable must be in SSA ...
                bool isInvariant = lclVar->HasSsaName();
                // and the SSA definition must be outside the loop we're hoisting from ...
                isInvariant = isInvariant &&
                              !m_loop->ContainsBlock(
                                  m_compiler->lvaGetDesc(lclNum)->GetPerSsaData(lclVar->GetSsaNum())->GetBlock());

                // and the VN of the tree is considered invariant as well.
                //
                // TODO-CQ: This VN invariance check should not be necessary and in some cases it is conservative - it
                // is possible that the SSA def is outside the loop but VN does not understand what the node is doing
                // (e.g. LCL_FLD-based type reinterpretation) and assigns a "new, unique VN" to the node. This VN is
                // associated with the block where the node is, a loop block, and thus the VN is considered to not be
                // invariant.
                // On the other hand, it is possible for a SSA def to be inside the loop yet the use to be invariant,
                // if the defining expression is also invariant. In such a case the VN invariance would help but it is
                // blocked by the SSA invariance check.
                isInvariant = isInvariant && IsTreeVNInvariant(tree);

                Value& top = m_valueStack.TopRef();
                assert(top.Node() == tree);

                if (isInvariant)
                {
                    top.m_invariant = true;
                    // In general it doesn't make sense to hoist a local node but there are exceptions, for example
                    // LCL_FLD nodes (because then the variable cannot be enregistered and the node always turns
                    // into a memory access).
                    top.m_hoistable = IsNodeHoistable(tree);
                }

#ifdef DEBUG
                if (!isInvariant)
                {
                    top.m_failReason = "local, not rvalue / not in SSA / defined within current loop";
                }
                else if (!top.m_hoistable)
                {
                    top.m_failReason = "not handled by cse";
                }
#endif

                JITDUMP("      [%06u] %s: %s: %s\n", dspTreeID(tree), GenTree::OpName(tree->OperGet()),
                        top.m_invariant ? (top.m_hoistable ? "hoistable" : "not hoistable") : "not invariant",
                        top.m_failReason);

                return fgWalkResult::WALK_CONTINUE;
            }

            bool treeIsCctorDependent     = tree->OperIsIndir() && ((tree->gtFlags & GTF_IND_INITCLASS) != 0);
            bool treeIsInvariant          = true;
            bool treeHasHoistableChildren = false;
            int  childCount;

#ifdef DEBUG
            const char* failReason = "unknown";
#endif

            for (childCount = 0; m_valueStack.TopRef(childCount).Node() != tree; childCount++)
            {
                Value& child = m_valueStack.TopRef(childCount);

                if (child.m_hoistable)
                {
                    treeHasHoistableChildren = true;
                }

                if (!child.m_invariant)
                {
                    treeIsInvariant = false;
                    INDEBUG(failReason = "variant child";)
                }

                if (child.m_cctorDependent)
                {
                    // Normally, a parent of a cctor-dependent tree is also cctor-dependent.
                    treeIsCctorDependent = true;

                    // Check for the case where we can stop propagating cctor-dependent upwards.
                    if (tree->OperIs(GT_COMMA) && (child.Node() == tree->gtGetOp2()))
                    {
                        GenTree* op1 = tree->gtGetOp1();
                        if (op1->OperIs(GT_CALL))
                        {
                            GenTreeCall* call = op1->AsCall();
                            if ((call->gtCallType == CT_HELPER) &&
                                s_helperCallProperties.MayRunCctor(eeGetHelperNum(call->gtCallMethHnd)))
                            {
                                // Hoisting the comma is ok because it would hoist the initialization along
                                // with the static field reference.
                                treeIsCctorDependent = false;
                                // Hoisting the static field without hoisting the initialization would be
                                // incorrect, make sure we consider the field (which we flagged as
                                // cctor-dependent) non-hoistable.
                                noway_assert(!child.m_hoistable);
                            }
                        }
                    }
                }
            }

            // If all the children of "tree" are hoistable, then "tree" itself can be hoisted,
            // unless it has a static var reference that can't be hoisted past its cctor call.
            bool treeIsHoistable = treeIsInvariant && !treeIsCctorDependent;

#ifdef DEBUG
            if (treeIsInvariant && !treeIsHoistable)
            {
                failReason = "cctor dependent";
            }
#endif

            // But we must see if anything else prevents "tree" from being hoisted.
            //
            if (treeIsInvariant)
            {
                if (treeIsHoistable)
                {
                    treeIsHoistable = IsNodeHoistable(tree);
                    if (!treeIsHoistable)
                    {
                        INDEBUG(failReason = "not handled by cse";)
                    }
                }

                // If it's a call, it must be a helper call, and be pure.
                // Further, if it may run a cctor, it must be labeled as "Hoistable"
                // (meaning it won't run a cctor because the class is not precise-init).
                if (treeIsHoistable && tree->IsCall())
                {
                    GenTreeCall* call = tree->AsCall();
                    if (call->gtCallType != CT_HELPER)
                    {
                        INDEBUG(failReason = "non-helper call";)
                        treeIsHoistable = false;
                    }
                    else
                    {
                        CorInfoHelpFunc helpFunc = eeGetHelperNum(call->gtCallMethHnd);
                        if (!s_helperCallProperties.IsPure(helpFunc))
                        {
                            INDEBUG(failReason = "impure helper call";)
                            treeIsHoistable = false;
                        }
                        else if (s_helperCallProperties.MayRunCctor(helpFunc) &&
                                 ((call->gtFlags & GTF_CALL_HOISTABLE) == 0))
                        {
                            INDEBUG(failReason = "non-hoistable helper call";)
                            treeIsHoistable = false;
                        }
                    }
                }

                if (treeIsHoistable)
                {
                    if (!m_beforeSideEffect)
                    {
                        // For now, we give up on an expression that might raise an exception if it is after the
                        // first possible global side effect (and we assume we're after that if we're not in the first
                        // block).
                        // TODO-CQ: this is when we might do loop cloning.
                        //
                        if ((tree->gtFlags & GTF_EXCEPT) != 0)
                        {
                            INDEBUG(failReason = "side effect ordering constraint";)
                            treeIsHoistable = false;
                        }
                    }
                }

                // Is the value of the whole tree loop invariant?
                treeIsInvariant = IsTreeVNInvariant(tree);

                // Is the value of the whole tree loop invariant?
                if (!treeIsInvariant)
                {
                    // Here we have a tree that is not loop invariant and we thus cannot hoist
                    INDEBUG(failReason = "tree VN is loop variant";)
                    treeIsHoistable = false;
                }
            }

            // Next check if we need to set 'm_beforeSideEffect' to false.
            //
            // If we have already set it to false then we can skip these checks
            //
            if (m_beforeSideEffect)
            {
                // Is the value of the whole tree loop invariant?
                if (!treeIsInvariant)
                {
                    // We have a tree that is not loop invariant and we thus cannot hoist
                    assert(treeIsHoistable == false);

                    // Check if we should clear m_beforeSideEffect.
                    // If 'tree' can throw an exception then we need to set m_beforeSideEffect to false.
                    // Note that calls are handled below
                    if (tree->OperMayThrow(m_compiler) && !tree->IsCall())
                    {
                        m_beforeSideEffect = false;
                    }
                }

                // In the section below, we only care about memory side effects.  We assume that expressions will
                // be hoisted so that they are evaluated in the same order as they would have been in the loop,
                // and therefore throw exceptions in the same order.
                //
                if (tree->IsCall())
                {
                    // If it's a call, it must be a helper call that does not mutate the heap.
                    // Further, if it may run a cctor, it must be labeled as "Hoistable"
                    // (meaning it won't run a cctor because the class is not precise-init).
                    GenTreeCall* call = tree->AsCall();
                    if (call->gtCallType != CT_HELPER)
                    {
                        m_beforeSideEffect = false;
                    }
                    else
                    {
                        CorInfoHelpFunc helpFunc = eeGetHelperNum(call->gtCallMethHnd);
                        if (s_helperCallProperties.MutatesHeap(helpFunc))
                        {
                            m_beforeSideEffect = false;
                        }
                        else if (s_helperCallProperties.MayRunCctor(helpFunc) &&
                                 (call->gtFlags & GTF_CALL_HOISTABLE) == 0)
                        {
                            m_beforeSideEffect = false;
                        }

                        // Additional check for helper calls that throw exceptions
                        if (!treeIsInvariant)
                        {
                            // We have a tree that is not loop invariant and we thus cannot hoist
                            assert(treeIsHoistable == false);

                            // Does this helper call throw?
                            if (!s_helperCallProperties.NoThrow(helpFunc))
                            {
                                m_beforeSideEffect = false;
                            }
                        }
                    }
                }
                else if (tree->OperRequiresAsgFlag())
                {
                    // Assume all stores except "STORE_LCL_VAR<non-addr-exposed lcl>(...)" are globally visible.
                    bool isGloballyVisibleStore;
                    if (tree->OperIsLocalStore())
                    {
                        isGloballyVisibleStore = m_compiler->lvaGetDesc(tree->AsLclVarCommon())->IsAddressExposed();
                    }
                    else
                    {
                        isGloballyVisibleStore = true;
                    }

                    if (isGloballyVisibleStore)
                    {
                        INDEBUG(failReason = "store to globally visible memory");
                        treeIsHoistable    = false;
                        m_beforeSideEffect = false;
                    }
                }
            }

            // If this 'tree' is hoistable then we return and the caller will
            // decide to hoist it as part of larger hoistable expression.
            //
            if (!treeIsHoistable && treeHasHoistableChildren)
            {
                // The current tree is not hoistable but it has hoistable children that we need
                // to hoist now.
                //
                // In order to preserve the original execution order, we also need to hoist any
                // other hoistable trees that we encountered so far.
                // At this point the stack contains (in top to bottom order):
                //   - the current node's children
                //   - the current node
                //   - ancestors of the current node and some of their descendants
                //
                // The ancestors have not been visited yet in post order so they're not hoistable
                // (and they cannot become hoistable because the current node is not) but some of
                // their descendants may have already been traversed and be hoistable.
                //
                // The execution order is actually bottom to top so we'll start hoisting from
                // the bottom of the stack, skipping the current node (which is expected to not
                // be hoistable).
                //
                // Note that the treeHasHoistableChildren check avoids unnecessary stack traversing
                // and also prevents hoisting trees too early. If the current tree is not hoistable
                // and it doesn't have any hoistable children then there's no point in hoisting any
                // other trees. Doing so would interfere with the cctor dependent case, where the
                // cctor dependent node is initially not hoistable and may become hoistable later,
                // when its parent comma node is visited.
                //
                // TODO-CQ: Ideally, we should be hoisting all the nodes having side-effects in execution
                // order as well as the ones that don't have side-effects at all. However, currently, we
                // just restrict hoisting a node(s) (that are children of `comma`) if one of the siblings
                // (which is executed before the given node) has side-effects (exceptions). Descendants
                // of ancestors might have side-effects and we might hoist nodes past them. This needs
                // to be addressed properly.
                bool visitedCurr = false;
                bool isCommaTree = tree->OperIs(GT_COMMA);
                bool hasExcep    = false;
                for (int i = 0; i < m_valueStack.Height(); i++)
                {
                    Value& value = m_valueStack.BottomRef(i);

                    if (value.m_hoistable)
                    {
                        assert(value.Node() != tree);

                        if (IsHoistableOverExcepSibling(value.Node(), hasExcep))
                        {
                            m_compiler->optHoistCandidate(value.Node(), m_currentBlock, m_loop, m_hoistContext);
                        }

                        // Don't hoist this tree again.
                        value.m_hoistable = false;
                        value.m_invariant = false;
                    }
                    else if (value.Node() != tree)
                    {
                        if (visitedCurr && isCommaTree)
                        {
                            // If we have visited current tree, now we are visiting children.
                            // For GT_COMMA nodes, we want to track if any children throws and
                            // should not hoist further children past it.
                            hasExcep = (tree->gtFlags & GTF_EXCEPT) != 0;
                        }
                        JITDUMP("      [%06u] %s: %s\n", dspTreeID(value.Node()),
                                value.m_invariant ? "not hoistable" : "not invariant", value.m_failReason);
                    }
                    else
                    {
                        visitedCurr = true;
                        JITDUMP("      [%06u] not hoistable : current node\n", dspTreeID(value.Node()));
                    }
                }
            }

            m_valueStack.Pop(childCount);

            Value& top = m_valueStack.TopRef();
            assert(top.Node() == tree);
            top.m_hoistable      = treeIsHoistable;
            top.m_cctorDependent = treeIsCctorDependent;
            top.m_invariant      = treeIsInvariant;

#ifdef DEBUG
            if (!top.m_invariant || !top.m_hoistable)
            {
                top.m_failReason = failReason;
            }
#endif

            return fgWalkResult::WALK_CONTINUE;
        }
    };

    HoistVisitor visitor(this, loop, hoistContext);

    while (!blocks->Empty())
    {
        BasicBlock* block       = blocks->Pop();
        weight_t    blockWeight = block->getBBWeight(this);

        JITDUMP("\n    optHoistLoopBlocks " FMT_BB " (weight=%6s) of loop " FMT_LP " (head: " FMT_BB ")\n",
                block->bbNum, refCntWtd2str(blockWeight, /* padForDecimalPlaces */ true), loop->GetIndex(),
                loop->GetHeader()->bbNum);

        if (blockWeight < (BB_UNITY_WEIGHT / 10))
        {
            JITDUMP("      block weight is too small to perform hoisting.\n");
            continue;
        }

        visitor.HoistBlock(block);
    }

    hoistContext->ResetHoistedInCurLoop();
}

void Compiler::optHoistCandidate(GenTree*              tree,
                                 BasicBlock*           treeBb,
                                 FlowGraphNaturalLoop* loop,
                                 LoopHoistContext*     hoistCtxt)
{
    // It must pass the hoistable profitablity tests for this loop level
    if (!optIsProfitableToHoistTree(tree, loop, hoistCtxt))
    {
        JITDUMP("   ... not profitable to hoist\n");
        return;
    }

    if (hoistCtxt->GetHoistedInCurLoop(this)->Lookup(tree->gtVNPair.GetLiberal()))
    {
        // already hoisted this expression in the current loop, so don't hoist this expression.

        JITDUMP("      [%06u] ... already hoisted " FMT_VN " in " FMT_LP "\n ", dspTreeID(tree),
                tree->gtVNPair.GetLiberal(), loop->GetIndex());
        return;
    }

    // We should already have a pre-header for the loop.
    assert(loop->EntryEdges().size() == 1);
    BasicBlock* preheader = loop->EntryEdge(0)->getSourceBlock();

    // If the block we're hoisting from and the pre-header are in different EH regions, don't hoist.
    // TODO: we could probably hoist things that won't raise exceptions, such as constants.
    if (!BasicBlock::sameTryRegion(preheader, treeBb))
    {
        JITDUMP("   ... not hoisting in " FMT_LP ", eh region constraint (pre-header try index %d, candidate " FMT_BB
                " try index %d\n",
                loop->GetIndex(), preheader->bbTryIndex, treeBb->bbNum, treeBb->bbTryIndex);
        return;
    }

    // Expression can be hoisted
    optPerformHoistExpr(tree, treeBb, loop);

    // Increment lpHoistedExprCount or lpHoistedFPExprCount
    if (varTypeUsesIntReg(tree))
    {
        hoistCtxt->m_hoistedExprCount++;
#ifndef TARGET_64BIT
        // For our 32-bit targets Long types take two registers.
        if (varTypeIsLong(tree->TypeGet()))
        {
            hoistCtxt->m_hoistedExprCount++;
        }
#endif
    }
#ifdef TARGET_XARCH
    else if (varTypeUsesMaskReg(tree))
    {
        hoistCtxt->m_hoistedMskExprCount++;
    }
#endif // TARGET_XARCH
    else
    {
        assert(varTypeUsesFloatReg(tree));
        hoistCtxt->m_hoistedFPExprCount++;
    }

    // Record the hoisted expression in hoistCtxt
    hoistCtxt->GetHoistedInCurLoop(this)->Set(tree->gtVNPair.GetLiberal(), true);
}

bool Compiler::optVNIsLoopInvariant(ValueNum vn, FlowGraphNaturalLoop* loop, VNSet* loopVnInvariantCache)
{
    // If it is not a VN, is not loop-invariant.
    if (vn == ValueNumStore::NoVN)
    {
        return false;
    }

    // We'll always short-circuit constants.
    if (vnStore->IsVNConstant(vn) || vn == vnStore->VNForVoid())
    {
        return true;
    }

    // If we've done this query previously, don't repeat.
    bool previousRes = false;
    if (loopVnInvariantCache->Lookup(vn, &previousRes))
    {
        return previousRes;
    }

    bool      res = true;
    VNFuncApp funcApp;
    if (vnStore->GetVNFunc(vn, &funcApp))
    {
        if (funcApp.m_func == VNF_PhiDef)
        {
            // Is the definition within the loop?  If so, is not loop-invariant.
            unsigned      lclNum = funcApp.m_args[0];
            unsigned      ssaNum = funcApp.m_args[1];
            LclSsaVarDsc* ssaDef = lvaTable[lclNum].GetPerSsaData(ssaNum);
            res                  = !loop->ContainsBlock(ssaDef->GetBlock());
        }
        else if (funcApp.m_func == VNF_PhiMemoryDef)
        {
            BasicBlock* defnBlk = reinterpret_cast<BasicBlock*>(vnStore->ConstantValue<ssize_t>(funcApp.m_args[0]));
            res                 = !loop->ContainsBlock(defnBlk);
        }
        else if (funcApp.m_func == VNF_MemOpaque)
        {
            const unsigned loopIndex = funcApp.m_args[0];

            // Check for the special "ambiguous" loop index.
            // This is considered variant in every loop.
            //
            if (loopIndex == ValueNumStore::UnknownLoop)
            {
                res = false;
            }
            else if (loopIndex == ValueNumStore::NoLoop)
            {
                res = true;
            }
            else
            {
                FlowGraphNaturalLoop* otherLoop = m_loops->GetLoopByIndex(loopIndex);
                assert(otherLoop != nullptr);
                res = !loop->ContainsLoop(otherLoop);
            }
        }
        else
        {
            for (unsigned i = 0; i < funcApp.m_arity; i++)
            {
                // 4th arg of mapStore identifies the loop where the store happens.
                //
                if (funcApp.m_func == VNF_MapStore)
                {
                    assert(funcApp.m_arity == 4);

                    if (i == 3)
                    {
                        const unsigned loopIndex = funcApp.m_args[3];
                        assert((loopIndex == ValueNumStore::NoLoop) || (loopIndex < m_loops->NumLoops()));
                        if (loopIndex == ValueNumStore::NoLoop)
                        {
                            res = true;
                        }
                        else
                        {
                            FlowGraphNaturalLoop* otherLoop = m_loops->GetLoopByIndex(loopIndex);
                            res                             = !loop->ContainsLoop(otherLoop);
                        }
                        break;
                    }
                }

                // TODO-CQ: We need to either make sure that *all* VN functions
                // always take VN args, or else have a list of arg positions to exempt, as implicitly
                // constant.
                if (!optVNIsLoopInvariant(funcApp.m_args[i], loop, loopVnInvariantCache))
                {
                    res = false;
                    break;
                }
            }
        }
    }

    loopVnInvariantCache->Set(vn, res);
    return res;
}

//------------------------------------------------------------------------------
// fgSetEHRegionForNewPreheader: Set the EH region for a newly inserted
// preheader.
//
// In which EH region should the header live?
//
// The preheader block is expected to have been added immediately before a
// block `next` in the loop that is also in the same EH region as the header.
// This is usually the lexically first block of the loop, but may also be the
// header itself.
//
// If the `next` block is NOT the first block of a `try` region, the preheader
// can simply extend the header block's EH region.
//
// If the `next` block IS the first block of a `try`, we find its parent region
// and use that. For mutual-protect regions, we need to find the actual parent,
// as the block stores the most "nested" mutual region. For non-mutual-protect
// regions, due to EH canonicalization, we are guaranteed that no other EH
// regions begin on the same block, so looking to just the parent is
// sufficient. Note that we can't just extend the EH region of the header to
// the preheader, because the header will still be the target of backward
// branches from within the loop. If those backward branches come from outside
// the `try` (say, only the top half of the loop is a `try` region), then we
// can't branch to a non-first `try` region block (you always must enter the
// `try` in the first block).
//
// Note that hoisting any code out of a try region, for example, to a preheader
// block in a different EH region, needs to ensure that no exceptions will be
// thrown.
//
// Arguments:
//    preheader - the new preheader block, which has already been added to the
//                block list before a block inside the loop that shares EH
//                region with the header.
//
void Compiler::fgSetEHRegionForNewPreheader(BasicBlock* preheader)
{
    BasicBlock* next = preheader->Next();

    if (bbIsTryBeg(next))
    {
        // `next` is the beginning of a try block. Figure out the EH region to use.
        assert(next->hasTryIndex());
        unsigned newTryIndex = ehTrueEnclosingTryIndexIL(next->getTryIndex());
        if (newTryIndex == EHblkDsc::NO_ENCLOSING_INDEX)
        {
            // No EH try index.
            preheader->clearTryIndex();
        }
        else
        {
            preheader->setTryIndex(newTryIndex);
        }

        // What handler region to use? Use the same handler region as `next`.
        preheader->copyHndIndex(next);
    }
    else
    {
        fgExtendEHRegionBefore(next);
    }
}

//------------------------------------------------------------------------------
// fgCanonicalizeFirstBB: Canonicalize the method entry for loop and dominator
// purposes.
//
// Returns:
//   Suitable phase status.
//
PhaseStatus Compiler::fgCanonicalizeFirstBB()
{
    if (fgFirstBB->hasTryIndex())
    {
        JITDUMP("Canonicalizing entry because it currently is the beginning of a try region\n");
    }
    else if (fgFirstBB->bbPreds != nullptr)
    {
        JITDUMP("Canonicalizing entry because it currently has predecessors\n");
    }
    else
    {
        return PhaseStatus::MODIFIED_NOTHING;
    }

    assert(!fgFirstBBisScratch());
    fgEnsureFirstBBisScratch();
    // TODO-Quirk: Remove
    fgCanonicalizedFirstBB = true;
    return PhaseStatus::MODIFIED_EVERYTHING;
}

LoopSideEffects::LoopSideEffects() : VarInOut(VarSetOps::UninitVal()), VarUseDef(VarSetOps::UninitVal())
{
    for (MemoryKind mk : allMemoryKinds())
    {
        HasMemoryHavoc[mk] = false;
    }
}

void Compiler::optComputeLoopSideEffects()
{
    m_loopSideEffects =
        m_loops->NumLoops() == 0 ? nullptr : (new (this, CMK_LoopOpt) LoopSideEffects[m_loops->NumLoops()]);

    for (FlowGraphNaturalLoop* loop : m_loops->InReversePostOrder())
    {
        m_loopSideEffects[loop->GetIndex()].VarInOut  = VarSetOps::MakeEmpty(this);
        m_loopSideEffects[loop->GetIndex()].VarUseDef = VarSetOps::MakeEmpty(this);
    }

    BasicBlock** postOrder      = m_dfsTree->GetPostOrder();
    unsigned     postOrderCount = m_dfsTree->GetPostOrderCount();

    // Iterate all blocks in loops.
    for (FlowGraphNaturalLoop* loop : m_loops->InReversePostOrder())
    {
        if (loop->GetParent() != nullptr)
        {
            continue;
        }

        // The side effect code benefits from seeing things in RPO as it has some
        // limited treatment assignments it has seen the value of.
        loop->VisitLoopBlocksReversePostOrder([=](BasicBlock* loopBlock) {
            FlowGraphNaturalLoop* loop = m_blockToLoop->GetLoop(loopBlock);
            assert(loop != nullptr);
            optComputeLoopSideEffectsOfBlock(loopBlock, loop);

            return BasicBlockVisit::Continue;
        });
    }
}

void Compiler::optComputeInterestingVarSets()
{
    VarSetOps::AssignNoCopy(this, lvaFloatVars, VarSetOps::MakeEmpty(this));
#ifndef TARGET_64BIT
    VarSetOps::AssignNoCopy(this, lvaLongVars, VarSetOps::MakeEmpty(this));
#endif
#ifdef TARGET_XARCH
    VarSetOps::AssignNoCopy(this, lvaMaskVars, VarSetOps::MakeEmpty(this));
#endif

    for (unsigned i = 0; i < lvaCount; i++)
    {
        LclVarDsc* varDsc = lvaGetDesc(i);
        if (varDsc->lvTracked)
        {
            if (varTypeUsesFloatReg(varDsc->lvType))
            {
                VarSetOps::AddElemD(this, lvaFloatVars, varDsc->lvVarIndex);
            }
#ifndef TARGET_64BIT
            else if (varTypeIsLong(varDsc->lvType))
            {
                VarSetOps::AddElemD(this, lvaLongVars, varDsc->lvVarIndex);
            }
#endif
#ifdef TARGET_XARCH
            else if (varTypeUsesMaskReg(varDsc->lvType))
            {
                VarSetOps::AddElemD(this, lvaMaskVars, varDsc->lvVarIndex);
            }
#endif // TARGET_XARCH
        }
    }
}

void Compiler::optRecordLoopNestsMemoryHavoc(FlowGraphNaturalLoop* loop, MemoryKindSet memoryHavoc)
{
    do
    {
        for (MemoryKind memoryKind : allMemoryKinds())
        {
            if ((memoryHavoc & memoryKindSet(memoryKind)) != 0)
            {
                m_loopSideEffects[loop->GetIndex()].HasMemoryHavoc[memoryKind] = true;
            }
        }

        loop = loop->GetParent();
    } while (loop != nullptr);
}

void Compiler::optComputeLoopSideEffectsOfBlock(BasicBlock* blk, FlowGraphNaturalLoop* mostNestedLoop)
{
    JITDUMP("optComputeLoopSideEffectsOfBlock " FMT_BB ", mostNestedLoop " FMT_LP "\n", blk->bbNum,
            mostNestedLoop->GetIndex());
    AddVariableLivenessAllContainingLoops(mostNestedLoop, blk);

    // MemoryKinds for which an in-loop call or store has arbitrary effects.
    MemoryKindSet memoryHavoc = emptyMemoryKindSet;

    // Now iterate over the remaining statements, and their trees.
    for (Statement* const stmt : blk->NonPhiStatements())
    {
        for (GenTree* const tree : stmt->TreeList())
        {
            genTreeOps oper = tree->OperGet();

            // Even after we set memoryHavoc we still may want to know if a loop contains calls
            if (memoryHavoc == fullMemoryKindSet)
            {
                if (oper == GT_CALL)
                {
                    // Record that this loop contains a call
                    AddContainsCallAllContainingLoops(mostNestedLoop);
                }

                // If we just marked it as containing a call or it was previously set
                if (m_loopSideEffects[mostNestedLoop->GetIndex()].ContainsCall)
                {
                    // We can early exit after both memoryHavoc and ContainsCall are both set to true.
                    break;
                }

                // We are just looking for GT_CALL nodes after memoryHavoc was set.
                continue;
            }

            // otherwise memoryHavoc is not set for at least one heap ID
            assert(memoryHavoc != fullMemoryKindSet);

            // This body is a distillation of the memory side-effect code of value numbering.
            // We also do a very limited analysis if byref PtrTo values, to cover some cases
            // that the compiler creates.
            switch (oper)
            {
                case GT_STORE_LCL_VAR:
                case GT_STORE_LCL_FLD:
                {
                    GenTreeLclVarCommon* lcl    = tree->AsLclVarCommon();
                    ValueNum             dataVN = lcl->Data()->gtVNPair.GetLiberal();

                    // If we gave the data a value number, propagate it.
                    if (lcl->OperIs(GT_STORE_LCL_VAR) && (dataVN != ValueNumStore::NoVN))
                    {
                        dataVN = vnStore->VNNormalValue(dataVN);
                        if (lcl->HasSsaName())
                        {
                            lvaTable[lcl->GetLclNum()].GetPerSsaData(lcl->GetSsaNum())->m_vnPair.SetLiberal(dataVN);
                        }
                    }

                    // If the local is address-exposed, count this as ByrefExposed havoc
                    if (lvaVarAddrExposed(lcl->GetLclNum()))
                    {
                        memoryHavoc |= memoryKindSet(ByrefExposed);
                    }
                }
                break;

                case GT_STOREIND:
                case GT_STORE_BLK:
                {
                    if (tree->AsIndir()->IsVolatile())
                    {
                        memoryHavoc |= memoryKindSet(GcHeap, ByrefExposed);
                        continue;
                    }

                    GenTree* addr = tree->AsIndir()->Addr()->gtEffectiveVal();

                    if (addr->TypeGet() == TYP_BYREF && addr->OperGet() == GT_LCL_VAR)
                    {
                        // If it's a local byref for which we recorded a value number, use that...
                        GenTreeLclVar* argLcl = addr->AsLclVar();
                        if (argLcl->HasSsaName())
                        {
                            ValueNum argVN =
                                lvaTable[argLcl->GetLclNum()].GetPerSsaData(argLcl->GetSsaNum())->m_vnPair.GetLiberal();
                            VNFuncApp funcApp;
                            if (argVN != ValueNumStore::NoVN && vnStore->GetVNFunc(argVN, &funcApp) &&
                                funcApp.m_func == VNF_PtrToArrElem)
                            {
                                assert(vnStore->IsVNHandle(funcApp.m_args[0]));
                                CORINFO_CLASS_HANDLE elemType =
                                    CORINFO_CLASS_HANDLE(vnStore->ConstantValue<size_t>(funcApp.m_args[0]));
                                AddModifiedElemTypeAllContainingLoops(mostNestedLoop, elemType);
                                // Don't set memoryHavoc for GcHeap below.  Do set memoryHavoc for ByrefExposed
                                // (conservatively assuming that a byref may alias the array element)
                                memoryHavoc |= memoryKindSet(ByrefExposed);
                                continue;
                            }
                        }
                        // Otherwise...
                        memoryHavoc |= memoryKindSet(GcHeap, ByrefExposed);
                    }
                    else
                    {
                        GenTreeArrAddr* arrAddr  = nullptr;
                        GenTree*        baseAddr = nullptr;
                        FieldSeq*       fldSeq   = nullptr;
                        ssize_t         offset   = 0;

                        if (addr->IsArrayAddr(&arrAddr))
                        {
                            // We will not collect "fldSeq" -- any modification to an S[], at
                            // any field of "S", will lose all information about the array type.
                            CORINFO_CLASS_HANDLE elemTypeEq =
                                EncodeElemType(arrAddr->GetElemType(), arrAddr->GetElemClassHandle());
                            AddModifiedElemTypeAllContainingLoops(mostNestedLoop, elemTypeEq);
                            // Conservatively assume byrefs may alias this array element
                            memoryHavoc |= memoryKindSet(ByrefExposed);
                        }
                        else if (addr->IsFieldAddr(this, &baseAddr, &fldSeq, &offset))
                        {
                            assert(fldSeq != nullptr);

                            FieldKindForVN fieldKind =
                                (baseAddr != nullptr) ? FieldKindForVN::WithBaseAddr : FieldKindForVN::SimpleStatic;
                            AddModifiedFieldAllContainingLoops(mostNestedLoop, fldSeq->GetFieldHandle(), fieldKind);
                            // Conservatively assume byrefs may alias this object.
                            memoryHavoc |= memoryKindSet(ByrefExposed);
                        }
                        else
                        {
                            memoryHavoc |= memoryKindSet(GcHeap, ByrefExposed);
                        }
                    }
                }
                break;

                case GT_COMMA:
                    tree->gtVNPair = tree->AsOp()->gtOp2->gtVNPair;
                    break;

                // Is it an addr of an array index expression?
                case GT_ARR_ADDR:
                {
                    CORINFO_CLASS_HANDLE elemTypeEq =
                        EncodeElemType(tree->AsArrAddr()->GetElemType(), tree->AsArrAddr()->GetElemClassHandle());
                    ValueNum elemTypeEqVN = vnStore->VNForHandle(ssize_t(elemTypeEq), GTF_ICON_CLASS_HDL);

                    // Label this with a "dummy" PtrToArrElem so that we pick it up when looking at the ASG.
                    ValueNum ptrToArrElemVN =
                        vnStore->VNForFunc(TYP_BYREF, VNF_PtrToArrElem, elemTypeEqVN, vnStore->VNForNull(),
                                           vnStore->VNForNull(), vnStore->VNForNull());
                    tree->gtVNPair.SetBoth(ptrToArrElemVN);
                }
                break;

#ifdef FEATURE_HW_INTRINSICS
                case GT_HWINTRINSIC:
                {
                    GenTreeHWIntrinsic* hwintrinsic = tree->AsHWIntrinsic();
                    NamedIntrinsic      intrinsicId = hwintrinsic->GetHWIntrinsicId();

                    if (hwintrinsic->OperIsMemoryStoreOrBarrier())
                    {
                        // For barriers, we model the behavior after GT_MEMORYBARRIER
                        memoryHavoc |= memoryKindSet(GcHeap, ByrefExposed);
                    }
                    break;
                }
#endif // FEATURE_HW_INTRINSICS

                case GT_LOCKADD:
                case GT_XORR:
                case GT_XAND:
                case GT_XADD:
                case GT_XCHG:
                case GT_CMPXCHG:
                case GT_MEMORYBARRIER:
                case GT_STORE_DYN_BLK:
                {
                    memoryHavoc |= memoryKindSet(GcHeap, ByrefExposed);
                }
                break;

                case GT_CALL:
                {
                    GenTreeCall* call = tree->AsCall();

                    // Record that this loop contains a call
                    AddContainsCallAllContainingLoops(mostNestedLoop);

                    if (call->gtCallType == CT_HELPER)
                    {
                        CorInfoHelpFunc helpFunc = eeGetHelperNum(call->gtCallMethHnd);
                        if (s_helperCallProperties.MutatesHeap(helpFunc))
                        {
                            memoryHavoc |= memoryKindSet(GcHeap, ByrefExposed);
                        }
                        else if (s_helperCallProperties.MayRunCctor(helpFunc))
                        {
                            // If the call is labeled as "Hoistable", then we've checked the
                            // class that would be constructed, and it is not precise-init, so
                            // the cctor will not be run by this call.  Otherwise, it might be,
                            // and might have arbitrary side effects.
                            if ((tree->gtFlags & GTF_CALL_HOISTABLE) == 0)
                            {
                                memoryHavoc |= memoryKindSet(GcHeap, ByrefExposed);
                            }
                        }
                    }
                    else
                    {
                        memoryHavoc |= memoryKindSet(GcHeap, ByrefExposed);
                    }
                    break;
                }

                default:
                    // All other gtOper node kinds, leave 'memoryHavoc' unchanged (i.e. false)
                    assert(!tree->OperRequiresAsgFlag());
                    break;
            }
        }

        // Clear the Value Number from the statement root node, if it was set above. This is to
        // ensure that for those blocks that are unreachable, which we still handle in this loop
        // but not during Value Numbering, fgDebugCheckExceptionSets() will skip the trees. Ideally,
        // we wouldn't be touching the gtVNPair at all (here) before actual Value Numbering.
        stmt->GetRootNode()->gtVNPair.SetBoth(ValueNumStore::NoVN);
    }

    if (memoryHavoc != emptyMemoryKindSet)
    {
        // Record that all loops containing this block have this kind of memoryHavoc effects.
        optRecordLoopNestsMemoryHavoc(mostNestedLoop, memoryHavoc);
    }
}

// Marks the containsCall information to "loop" and any parent loops.
void Compiler::AddContainsCallAllContainingLoops(FlowGraphNaturalLoop* loop)
{
    do
    {
        m_loopSideEffects[loop->GetIndex()].ContainsCall = true;
        loop                                             = loop->GetParent();
    } while (loop != nullptr);
}

// Adds the variable liveness information for 'blk' to "lnum" and any parent loops.
void Compiler::AddVariableLivenessAllContainingLoops(FlowGraphNaturalLoop* loop, BasicBlock* blk)
{
    do
    {
        m_loopSideEffects[loop->GetIndex()].AddVariableLiveness(this, blk);
        loop = loop->GetParent();
    } while (loop != nullptr);
}

// Adds "fldHnd" to the set of modified fields of "loop" and any parent loops.
void Compiler::AddModifiedFieldAllContainingLoops(FlowGraphNaturalLoop* loop,
                                                  CORINFO_FIELD_HANDLE  fldHnd,
                                                  FieldKindForVN        fieldKind)
{
    do
    {
        m_loopSideEffects[loop->GetIndex()].AddModifiedField(this, fldHnd, fieldKind);
        loop = loop->GetParent();
    } while (loop != nullptr);
}

// Adds "elemType" to the set of modified array element types of "loop" and any parent loops.
void Compiler::AddModifiedElemTypeAllContainingLoops(FlowGraphNaturalLoop* loop, CORINFO_CLASS_HANDLE elemClsHnd)
{
    do
    {
        m_loopSideEffects[loop->GetIndex()].AddModifiedElemType(this, elemClsHnd);
        loop = loop->GetParent();
    } while (loop != nullptr);
}

//------------------------------------------------------------------------------
// optRemoveRangeCheck : Given an indexing node, mark it as not needing a range check.
//
// Arguments:
//    check  -  Range check tree, the raw CHECK node (ARRAY, SIMD or HWINTRINSIC).
//    comma  -  GT_COMMA to which the "check" belongs, "nullptr" if the check is a standalone one.
//    stmt   -  Statement the indexing nodes belong to.
//
// Return Value:
//    Rewritten "check" - no-op if it has no side effects or the tree that contains them.
//
// Notes:
//    This method is capable of removing checks of two kinds: COMMA-based and standalone top-level
//    ones. In case of a COMMA-based check, "check" must be a non-null first operand of a non-null
//    COMMA. In case of a standalone check, "comma" must be null and "check" - "stmt"'s root.
//
//    Does not keep costs or node threading up to date, but does update side effect flags.
//
GenTree* Compiler::optRemoveRangeCheck(GenTreeBoundsChk* check, GenTree* comma, Statement* stmt)
{
#if !REARRANGE_ADDS
    noway_assert(!"can't remove range checks without REARRANGE_ADDS right now");
#endif

    noway_assert(stmt != nullptr);
    noway_assert((comma != nullptr && comma->OperIs(GT_COMMA) && comma->gtGetOp1() == check) ||
                 (check != nullptr && check->OperIs(GT_BOUNDS_CHECK) && comma == nullptr));
    noway_assert(check->OperIs(GT_BOUNDS_CHECK));

    GenTree* tree = comma != nullptr ? comma : check;

#ifdef DEBUG
    if (verbose)
    {
        printf("Before optRemoveRangeCheck:\n");
        gtDispTree(tree);
    }
#endif

    // TODO-Bug: We really should be extracting all side effects from the
    // length and index here, but the length typically involves a GT_ARR_LENGTH
    // that we would preserve. Usually, as part of proving that the range check
    // passes, we have also proven that the ARR_LENGTH is non-faulting. We need
    // a good way to communicate to this function that it is ok to ignore side
    // effects of the ARR_LENGTH.
    GenTree* sideEffList = nullptr;
    gtExtractSideEffList(check->GetArrayLength(), &sideEffList, GTF_ASG);
    gtExtractSideEffList(check->GetIndex(), &sideEffList);

    if (sideEffList != nullptr)
    {
        // We've got some side effects.
        if (tree->OperIs(GT_COMMA))
        {
            // Make the comma handle them.
            tree->AsOp()->gtOp1 = sideEffList;
        }
        else
        {
            // Make the statement execute them instead of the check.
            stmt->SetRootNode(sideEffList);
            tree = sideEffList;
        }
    }
    else
    {
        check->gtBashToNOP();
    }

    if (tree->OperIs(GT_COMMA))
    {
        // TODO-CQ: We should also remove the GT_COMMA, but in any case we can no longer CSE the GT_COMMA.
        tree->gtFlags |= GTF_DONT_CSE;
    }

    gtUpdateSideEffects(stmt, tree);

#ifdef DEBUG
    if (verbose)
    {
        // gtUpdateSideEffects can update the side effects for ancestors in the tree, so display the whole statement
        // tree, not just the sub-tree.
        printf("After optRemoveRangeCheck for [%06u]:\n", dspTreeID(tree));
        gtDispTree(stmt->GetRootNode());
    }
#endif

    return check;
}

//------------------------------------------------------------------------------
// optRemoveStandaloneRangeCheck : A thin wrapper over optRemoveRangeCheck that removes standalone checks.
//
// Arguments:
//    check - The standalone top-level CHECK node.
//    stmt  - The statement "check" is a root node of.
//
// Return Value:
//    If "check" has no side effects, it is retuned, bashed to a no-op.
//    If it has side effects, the tree that executes them is returned.
//
GenTree* Compiler::optRemoveStandaloneRangeCheck(GenTreeBoundsChk* check, Statement* stmt)
{
    assert(check != nullptr);
    assert(stmt != nullptr);
    assert(check == stmt->GetRootNode());

    return optRemoveRangeCheck(check, nullptr, stmt);
}

//------------------------------------------------------------------------------
// optRemoveCommaBasedRangeCheck : A thin wrapper over optRemoveRangeCheck that removes COMMA-based checks.
//
// Arguments:
//    comma - GT_COMMA of which the first operand is the CHECK to be removed.
//    stmt  - The statement "comma" belongs to.
//
void Compiler::optRemoveCommaBasedRangeCheck(GenTree* comma, Statement* stmt)
{
    assert(comma != nullptr && comma->OperIs(GT_COMMA));
    assert(stmt != nullptr);
    assert(comma->gtGetOp1()->OperIs(GT_BOUNDS_CHECK));

    optRemoveRangeCheck(comma->gtGetOp1()->AsBoundsChk(), comma, stmt);
}

/*****************************************************************************
 * Return the scale in an array reference, given a pointer to the
 * multiplication node.
 */

ssize_t Compiler::optGetArrayRefScaleAndIndex(GenTree* mul, GenTree** pIndex DEBUGARG(bool bRngChk))
{
    assert(mul);
    assert(mul->gtOper == GT_MUL || mul->gtOper == GT_LSH);
    assert(mul->AsOp()->gtOp2->IsCnsIntOrI());

    ssize_t scale = mul->AsOp()->gtOp2->AsIntConCommon()->IconValue();

    if (mul->gtOper == GT_LSH)
    {
        scale = ((ssize_t)1) << scale;
    }

    GenTree* index = mul->AsOp()->gtOp1;

    if (index->gtOper == GT_MUL && index->AsOp()->gtOp2->IsCnsIntOrI())
    {
        // case of two cascading multiplications for constant int (e.g.  * 20 morphed to * 5 * 4):
        // When index->gtOper is GT_MUL and index->AsOp()->gtOp2->gtOper is GT_CNS_INT (i.e. * 5),
        //     we can bump up the scale from 4 to 5*4, and then change index to index->AsOp()->gtOp1.
        // Otherwise, we cannot optimize it. We will simply keep the original scale and index.
        scale *= index->AsOp()->gtOp2->AsIntConCommon()->IconValue();
        index = index->AsOp()->gtOp1;
    }

    assert(!bRngChk || index->gtOper != GT_COMMA);

    if (pIndex)
    {
        *pIndex = index;
    }

    return scale;
}

typedef JitHashTable<unsigned, JitSmallPrimitiveKeyFuncs<unsigned>, unsigned> LclVarRefCounts;

//------------------------------------------------------------------------------------------
// optRemoveRedundantZeroInits: Remove redundant zero initializations.
//
// Notes:
//    This phase iterates over basic blocks starting with the first basic block until there is no unique
//    basic block successor or until it detects a loop. It keeps track of local nodes it encounters.
//    When it gets to an assignment to a local variable or a local field, it checks whether the assignment
//    is the first reference to the local (or to the parent of the local field), and, if so,
//    it may do one of two optimizations:
//      1. If the following conditions are true:
//            the local is untracked,
//            the rhs of the assignment is 0,
//            the local is guaranteed to be fully initialized in the prolog,
//         then the explicit zero initialization is removed.
//      2. If the following conditions are true:
//            the assignment is to a local (and not a field),
//            the local is not lvLiveInOutOfHndlr or no exceptions can be thrown between the prolog and the assignment,
//            either the local has no gc pointers or there are no gc-safe points between the prolog and the assignment,
//         then the local is marked with lvHasExplicitInit which tells the codegen not to insert zero initialization
//         for this local in the prolog.

void Compiler::optRemoveRedundantZeroInits()
{
#ifdef DEBUG
    if (verbose)
    {
        printf("*************** In optRemoveRedundantZeroInits()\n");
    }
#endif // DEBUG

    CompAllocator   allocator(getAllocator(CMK_ZeroInit));
    LclVarRefCounts refCounts(allocator);
    BitVecTraits    bitVecTraits(lvaCount, this);
    BitVec          zeroInitLocals         = BitVecOps::MakeEmpty(&bitVecTraits);
    bool            hasGCSafePoint         = false;
    bool            hasImplicitControlFlow = false;

    assert(fgNodeThreading == NodeThreading::AllTrees);

    for (BasicBlock* block = fgFirstBB; (block != nullptr) && !block->HasFlag(BBF_MARKED);
         block             = block->GetUniqueSucc())
    {
        block->SetFlags(BBF_MARKED);
        CompAllocator   allocator(getAllocator(CMK_ZeroInit));
        LclVarRefCounts defsInBlock(allocator);
        bool            removedTrackedDefs = false;
        bool            hasEHSuccs         = block->HasPotentialEHSuccs(this);

        for (Statement* stmt = block->FirstNonPhiDef(); stmt != nullptr;)
        {
            Statement* next = stmt->GetNextStmt();
            for (GenTree* const tree : stmt->TreeList())
            {
                if (((tree->gtFlags & GTF_CALL) != 0))
                {
                    hasGCSafePoint = true;
                }

                hasImplicitControlFlow |= hasEHSuccs && ((tree->gtFlags & GTF_EXCEPT) != 0);

                switch (tree->gtOper)
                {
                    case GT_LCL_VAR:
                    case GT_LCL_FLD:
                    case GT_LCL_ADDR:
                    case GT_STORE_LCL_VAR:
                    case GT_STORE_LCL_FLD:
                    {
                        GenTreeLclVarCommon* lclNode   = tree->AsLclVarCommon();
                        unsigned             lclNum    = lclNode->GetLclNum();
                        unsigned*            pRefCount = refCounts.LookupPointer(lclNum);
                        if (pRefCount != nullptr)
                        {
                            *pRefCount = (*pRefCount) + 1;
                        }
                        else
                        {
                            refCounts.Set(lclNum, 1);
                        }

                        if ((tree->gtFlags & GTF_VAR_DEF) == 0)
                        {
                            break;
                        }

                        // We need to count the number of tracked var defs in the block
                        // so that we can update block->bbVarDef if we remove any tracked var defs.
                        LclVarDsc* const lclDsc = lvaGetDesc(lclNum);
                        if (lclDsc->lvTracked)
                        {
                            unsigned* pDefsCount = defsInBlock.LookupPointer(lclNum);
                            if (pDefsCount != nullptr)
                            {
                                *pDefsCount = (*pDefsCount) + 1;
                            }
                            else
                            {
                                defsInBlock.Set(lclNum, 1);
                            }
                        }
                        else if (varTypeIsStruct(lclDsc) && ((tree->gtFlags & GTF_VAR_USEASG) == 0) &&
                                 lvaGetPromotionType(lclDsc) != PROMOTION_TYPE_NONE)
                        {
                            for (unsigned i = lclDsc->lvFieldLclStart; i < lclDsc->lvFieldLclStart + lclDsc->lvFieldCnt;
                                 ++i)
                            {
                                if (lvaGetDesc(i)->lvTracked)
                                {
                                    unsigned* pDefsCount = defsInBlock.LookupPointer(i);
                                    if (pDefsCount != nullptr)
                                    {
                                        *pDefsCount = (*pDefsCount) + 1;
                                    }
                                    else
                                    {
                                        defsInBlock.Set(i, 1);
                                    }
                                }
                            }
                        }

                        if (!tree->OperIsLocalStore())
                        {
                            break;
                        }

                        // TODO-Cleanup: there is potential for cleaning this algorithm up by deleting
                        // double lookups of various reference counts. This is complicated somewhat by
                        // the present of LCL_ADDR (GTF_CALL_M_RETBUFFARG_LCLOPT) definitions.
                        pRefCount = refCounts.LookupPointer(lclNum);
                        if (*pRefCount != 1)
                        {
                            break;
                        }

                        unsigned parentRefCount = 0;
                        if (lclDsc->lvIsStructField && refCounts.Lookup(lclDsc->lvParentLcl, &parentRefCount) &&
                            (parentRefCount != 0))
                        {
                            break;
                        }

                        unsigned fieldRefCount = 0;
                        if (lclDsc->lvPromoted)
                        {
                            for (unsigned i = lclDsc->lvFieldLclStart;
                                 (fieldRefCount == 0) && (i < lclDsc->lvFieldLclStart + lclDsc->lvFieldCnt); ++i)
                            {
                                refCounts.Lookup(i, &fieldRefCount);
                            }
                        }

                        if (fieldRefCount != 0)
                        {
                            break;
                        }

                        // The local hasn't been referenced before this assignment.
                        bool removedExplicitZeroInit = false;
                        bool isEntire                = !tree->IsPartialLclFld(this);

                        if (tree->Data()->IsIntegralConst(0))
                        {
                            bool bbInALoop  = block->HasFlag(BBF_BACKWARD_JUMP);
                            bool bbIsReturn = block->KindIs(BBJ_RETURN);

                            if (!bbInALoop || bbIsReturn)
                            {
                                bool neverTracked = lclDsc->IsAddressExposed() || lclDsc->lvPinned ||
                                                    (lclDsc->lvPromoted && varTypeIsStruct(lclDsc));

                                if (BitVecOps::IsMember(&bitVecTraits, zeroInitLocals, lclNum) ||
                                    (lclDsc->lvIsStructField &&
                                     BitVecOps::IsMember(&bitVecTraits, zeroInitLocals, lclDsc->lvParentLcl)) ||
                                    ((neverTracked || !isEntire) &&
                                     !fgVarNeedsExplicitZeroInit(lclNum, bbInALoop, bbIsReturn)))
                                {
                                    // We are guaranteed to have a zero initialization in the prolog or a
                                    // dominating explicit zero initialization and the local hasn't been redefined
                                    // between the prolog and this explicit zero initialization so the assignment
                                    // can be safely removed.
                                    if (tree == stmt->GetRootNode())
                                    {
                                        fgRemoveStmt(block, stmt);
                                        removedExplicitZeroInit      = true;
                                        lclDsc->lvSuppressedZeroInit = 1;

                                        if (lclDsc->lvTracked)
                                        {
                                            removedTrackedDefs   = true;
                                            unsigned* pDefsCount = defsInBlock.LookupPointer(lclNum);
                                            *pDefsCount          = (*pDefsCount) - 1;
                                        }
                                    }
                                }

                                if (isEntire)
                                {
                                    BitVecOps::AddElemD(&bitVecTraits, zeroInitLocals, lclNum);
                                }
                                *pRefCount = 0;
                            }
                        }

                        if (!removedExplicitZeroInit && isEntire &&
                            (!hasImplicitControlFlow || (lclDsc->lvTracked && !lclDsc->lvLiveInOutOfHndlr)))
                        {
                            // If compMethodRequiresPInvokeFrame() returns true, lower may later
                            // insert a call to CORINFO_HELP_INIT_PINVOKE_FRAME which is a gc-safe point.
                            if (!lclDsc->HasGCPtr() ||
                                (!GetInterruptible() && !hasGCSafePoint && !compMethodRequiresPInvokeFrame()))
                            {
                                // The local hasn't been used and won't be reported to the gc between
                                // the prolog and this explicit initialization. Therefore, it doesn't
                                // require zero initialization in the prolog.
                                lclDsc->lvHasExplicitInit = 1;
                                lclNode->gtFlags |= GTF_VAR_EXPLICIT_INIT;
                                JITDUMP("Marking V%02u as having an explicit init\n", lclNum);
                            }
                        }
                        break;
                    }
                    default:
                        break;
                }
            }
            stmt = next;
        }

        if (removedTrackedDefs)
        {
            for (const unsigned int lclNum : LclVarRefCounts::KeyIteration(&defsInBlock))
            {
                if (defsInBlock[lclNum] == 0)
                {
                    VarSetOps::RemoveElemD(this, block->bbVarDef, lvaGetDesc(lclNum)->lvVarIndex);
                }
            }
        }
    }

    for (BasicBlock* block = fgFirstBB; (block != nullptr) && block->HasFlag(BBF_MARKED);
         block             = block->GetUniqueSucc())
    {
        block->RemoveFlags(BBF_MARKED);
    }
}

//------------------------------------------------------------------------
// optVNBasedDeadStoreRemoval: VN(value)-based dead store removal.
//
// The phase iterates over partial stores referenced by the SSA
// descriptors and deletes those which do not change the local's value.
//
// Return Value:
//    A suitable phase status.
//
PhaseStatus Compiler::optVNBasedDeadStoreRemoval()
{
#ifdef DEBUG
    static ConfigMethodRange JitEnableVNBasedDeadStoreRemovalRange;
    JitEnableVNBasedDeadStoreRemovalRange.EnsureInit(JitConfig.JitEnableVNBasedDeadStoreRemovalRange());

    if (!JitEnableVNBasedDeadStoreRemovalRange.Contains(info.compMethodHash()))
    {
        JITDUMP("VN-based dead store removal disabled by JitEnableVNBasedDeadStoreRemovalRange\n");
        return PhaseStatus::MODIFIED_NOTHING;
    }
#endif

    bool madeChanges = false;

    for (unsigned lclNum = 0; lclNum < lvaCount; lclNum++)
    {
        if (!lvaInSsa(lclNum))
        {
            continue;
        }

        LclVarDsc* varDsc   = lvaGetDesc(lclNum);
        unsigned   defCount = varDsc->lvPerSsaData.GetCount();
        if (defCount <= 1)
        {
            continue;
        }

        for (unsigned defIndex = 1; defIndex < defCount; defIndex++)
        {
            LclSsaVarDsc*        defDsc = varDsc->lvPerSsaData.GetSsaDefByIndex(defIndex);
            GenTreeLclVarCommon* store  = defDsc->GetDefNode();

            if (store != nullptr)
            {
                assert(store->OperIsLocalStore() && defDsc->m_vnPair.BothDefined());

                JITDUMP("Considering [%06u] for removal...\n", dspTreeID(store));

                if (store->GetLclNum() != lclNum)
                {
                    JITDUMP(" -- no; composite definition\n");
                    continue;
                }

                ValueNum oldStoreValue;
                if ((store->gtFlags & GTF_VAR_USEASG) == 0)
                {
                    LclSsaVarDsc* lastDefDsc = varDsc->lvPerSsaData.GetSsaDefByIndex(defIndex - 1);
                    if (lastDefDsc->GetBlock() != defDsc->GetBlock())
                    {
                        JITDUMP(" -- no; last def not in the same block\n");
                        continue;
                    }

                    if ((store->gtFlags & GTF_VAR_EXPLICIT_INIT) != 0)
                    {
                        // Removing explicit inits is not profitable for primitives and not safe for structs.
                        JITDUMP(" -- no; 'explicit init'\n");
                        continue;
                    }

                    // CQ heuristic: avoid removing defs of enregisterable locals where this is likely to
                    // make them "must-init", extending live ranges. Here we assume the first SSA def was
                    // the implicit "live-in" one, which is not guaranteed, but very likely.
                    if ((defIndex == 1) && (varDsc->TypeGet() != TYP_STRUCT))
                    {
                        JITDUMP(" -- no; first explicit def of a non-STRUCT local\n", lclNum);
                        continue;
                    }

                    oldStoreValue = lastDefDsc->m_vnPair.GetConservative();
                }
                else
                {
                    ValueNum oldLclValue = varDsc->GetPerSsaData(defDsc->GetUseDefSsaNum())->m_vnPair.GetConservative();
                    oldStoreValue =
                        vnStore->VNForLoad(VNK_Conservative, oldLclValue, lvaLclExactSize(lclNum), store->TypeGet(),
                                           store->AsLclFld()->GetLclOffs(), store->AsLclFld()->GetSize());
                }

                GenTree* data = store->AsLclVarCommon()->Data();
                ValueNum storeValue;
                if (store->TypeIs(TYP_STRUCT) && data->IsIntegralConst(0))
                {
                    storeValue = vnStore->VNForZeroObj(store->GetLayout(this));
                }
                else
                {
                    storeValue = data->GetVN(VNK_Conservative);
                }

                if (oldStoreValue == storeValue)
                {
                    JITDUMP("Removed dead store:\n");
                    DISPTREE(store);

                    // TODO-ASG: delete this hack.
                    GenTree* nop  = gtNewNothingNode();
                    data->gtNext  = nop;
                    nop->gtPrev   = data;
                    nop->gtNext   = store;
                    store->gtPrev = nop;

                    store->ChangeOper(GT_COMMA);
                    store->AsOp()->gtOp2 = nop;
                    store->gtType        = TYP_VOID;
                    store->SetAllEffectsFlags(data);
                    gtUpdateTreeAncestorsSideEffects(store);

                    madeChanges = true;
                }
                else
                {
                    JITDUMP(" -- no; not redundant\n");
                }
            }
        }
    }

    return madeChanges ? PhaseStatus::MODIFIED_EVERYTHING : PhaseStatus::MODIFIED_NOTHING;
}