Set up the shadow stack in LSSA

This paves the way for introducing some RPI/PI optimizations and also moves us
a bit closer to the model where all that's possible to do in IR is done in IR.

Setting up the shadow stack in IR is a tricky problem since we don't want to
spill it to an alloca even in debug code. We therefore modify how we refer
to the shadow stack:
1) For the main function, we use an untracked SSA local. Note how we are
   introducing a new concept here - usually all SSA locals are tracked.
2) For funclets, we repurpose the pre-existing PHYSREG node to allow us
   to refer to the LLVM argument directly.

However, the IR representation is just one part of the problem. Another is the
fact codegen needs to refer to the shadow stack directly, for debug info and helper
call generation purposes. Since some of this needs to happen "in the prolog", before
any IR is generated, we also introduce a concept of "late" and "early" prologs.
They are sequenced as follows:

 - "Early"  prolog - codegen (LLVM IR)
 - "Middle" prolog - LSSA (IR)
 - "Late"   prolog - codegen (LLVM IR)

This is almost a zero-diff change; the few diffs are due to the different
ordering of native stack init and shadow stack init for RPI methods.

Author: SingleAccretion

src/coreclr/jit/gentree.cpp

@@ -8178,7 +8178,7 @@ GenTree* Compiler::gtNewPhysRegNode(regNumber reg, var_types type)
 {
 #ifdef TARGET_ARM64
     assert(genIsValidIntReg(reg) || (reg == REG_SPBASE) || (reg == REG_FFR));
-#else
+#elif !defined(TARGET_WASM)
     assert(genIsValidIntReg(reg) || (reg == REG_SPBASE));
 #endif
     GenTree* result = new (this, GT_PHYSREG) GenTreePhysReg(reg, type);

src/coreclr/jit/llvm.h

@@ -285,7 +285,7 @@ class Llvm
 {
 private:
     static const unsigned SHADOW_STACK_ARG_INDEX = 0;
-    static const unsigned DEFAULT_SHADOW_STACK_ALIGNMENT = TARGET_POINTER_SIZE;
+    static const unsigned ORIGINAL_SHADOW_STACK_ARG_INDEX = 1;
     static const unsigned MIN_HEAP_OBJ_SIZE = TARGET_POINTER_SIZE * 2;
 
     void* const m_pEECorInfo; // TODO-LLVM: workaround for not changing the JIT/EE interface.
@@ -301,7 +301,6 @@ class Llvm
     // Lowering members.
     LIR::Range* m_currentRange = nullptr;
     SideEffectSet m_scratchSideEffects; // Used for IsInvariantInRange.
-    bool m_anyFilterFunclets = false;
 
     // Optimization facts provided by lowering.
     BooleanFact m_anyVirtuallyUnwindableCalleesViaLowering = BooleanFact::Unknown;
@@ -316,6 +315,7 @@ class Llvm
 
     // Shared between LSSA and codegen.
     bool m_anyAddressExposedOrPinnedShadowLocals = false;
+    GenTree* m_prologEnd = nullptr; // First 'user' node after the prolog.
 
     // Codegen members.
     llvm::IRBuilder<> _builder;
@@ -329,8 +329,6 @@ class Llvm
     EHRegionInfo* m_EHRegionsInfo;
     Value* m_exceptionThrownAddressValue = nullptr;
 
-    Value* m_rootFunctionShadowStackValue = nullptr;
-
     // Codegen emit context.
     unsigned m_currentLlvmFunctionIndex = ROOT_FUNC_IDX;
     unsigned m_currentProtectedRegionIndex = EHblkDsc::NO_ENCLOSING_INDEX;
@@ -344,10 +342,9 @@ class Llvm
     unsigned m_lineNumberCount;
     CORINFO_LLVM_LINE_NUMBER_DEBUG_INFO* m_lineNumbers;
 
-    unsigned m_shadowFrameAlignment = DEFAULT_SHADOW_STACK_ALIGNMENT;
     unsigned _shadowStackLocalsSize = 0;
-    unsigned _originalShadowStackLclNum = BAD_VAR_NUM;
-    unsigned _shadowStackLclNum = BAD_VAR_NUM;
+    unsigned m_shadowStackSsaNum = SsaConfig::RESERVED_SSA_NUM;
+    unsigned m_shadowStackLclNum = BAD_VAR_NUM;
     unsigned m_sparseVirtualUnwindFrameLclNum = BAD_VAR_NUM;
     unsigned m_preciseVirtualUnwindFrameLclNum = BAD_VAR_NUM;
     unsigned _llvmArgCount = 0;
@@ -473,7 +470,6 @@ class Llvm
     void lowerVirtualStubCall(GenTreeCall* callNode);
     void insertNullCheckForCall(GenTreeCall* callNode);
     void lowerDelegateInvoke(GenTreeCall* callNode);
-    void lowerReversePInvokeExit(GenTreeCall* callNode);
     void lowerUnmanagedCall(GenTreeCall* callNode);
     void lowerCallToShadowStack(GenTreeCall* callNode);
     void lowerCallReturn(GenTreeCall* callNode);
@@ -485,7 +481,6 @@ class Llvm
     GenTree* normalizeStructUse(LIR::Use& use, ClassLayout* layout);
 
     unsigned representAsLclVar(LIR::Use& use);
-    GenTree* insertShadowStackAddr(GenTree* insertBefore, unsigned offset, unsigned shadowStackLclNum);
     GenTreeAddrMode* createAddrModeNode(GenTree* base, unsigned offset);
 
     void lowerCollectOptimizationFacts(GenTree* node);
@@ -496,7 +491,7 @@ class Llvm
     void dissolvePromotedLocal(unsigned lclNum);
 
     bool isFirstBlockCanonical();
-    GenTree* lowerAndInsertIntoFirstBlock(LIR::Range& range, GenTree* insertAfter = nullptr);
+    GenTree* lowerAndInsertIntoFirstBlock(LIR::Range&& range, GenTree* insertAfter = nullptr);
 
 public:
     PhaseStatus AddVirtualUnwindFrame();
@@ -546,8 +541,6 @@ class Llvm
         bool callIsInTry, bool callIsInFilter DEBUGARG(const char** pReasonWhyNot = nullptr)) const;
     bool isPotentialGcSafePoint(GenTree* node) const;
     bool isShadowFrameLocal(LclVarDsc* varDsc) const;
-    bool isShadowStackLocal(unsigned lclNum) const;
-    bool isFuncletParameter(unsigned lclNum) const;
 
     // ================================================================================================================
     // |                                                   Codegen                                                    |
@@ -561,14 +554,14 @@ class Llvm
 
     void initializeFunctions();
     void annotateFunctions();
-    void generateProlog();
-    void initializeShadowStack();
+    void generateEarlyProlog();
     void initializeLocals();
     void initializeBlocks();
+    void generateLateProlog();
     void generateUnwindBlocks();
     void generateBlocks();
     void generateBlock(BasicBlock* block);
-    void fillPhis();
+    void generatePhis();
     void generateAuxiliaryArtifacts();
     void verifyGeneratedCode();
     void displayGeneratedCode();
@@ -595,6 +588,7 @@ class Llvm
     void buildCmp(GenTreeOp* node);
     void buildCnsDouble(GenTreeDblCon* node);
     void buildIntegralConst(GenTreeIntConCommon* node);
+    void buildPhysReg(GenTreePhysReg* physReg);
     void buildCall(GenTreeCall* node);
     void buildInd(GenTreeIndir* indNode);
     void buildBlk(GenTreeBlk* blkNode);
@@ -669,7 +663,6 @@ class Llvm
     llvm::Constant* getIntPtrConst(target_size_t value, Type* llvmType = nullptr);
     Value* getShadowStack();
     Value* getShadowStackForCallee(bool isTailCall = false);
-    Value* getOriginalShadowStack();
 
     void setCurrentEmitContextForBlock(BasicBlock* block);
     void setCurrentEmitContextBlocks(LlvmBlockRange* llvmBlocks);
@@ -693,7 +686,7 @@ class Llvm
     LlvmBlockRange* getLlvmBlocksForBlock(BasicBlock* block);
     llvm::BasicBlock* getFirstLlvmBlockForBlock(BasicBlock* block);
     llvm::BasicBlock* getLastLlvmBlockForBlock(BasicBlock* block);
-    llvm::BasicBlock* getOrCreatePrologLlvmBlockForFunction(unsigned funcIdx);
+    llvm::IRBuilderBase::InsertPoint getOrCreateEarlyPrologForFunction(unsigned funcIdx);
 
     bool isReachable(BasicBlock* block) const;
     BasicBlock* getFirstBlockForFunction(unsigned funcIdx) const;