[SCEV] Expose getGEPExpr without needing to pass GEPOperator* (NFC) (llvm#164487)

Add a new getGEPExpr variant which is independent of GEPOperator*.

To be used to construct SCEVs for VPlan recipes in
llvm#161276.

PR: llvm#164487

Author: fhahn

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -638,8 +638,12 @@ class ScalarEvolution {
   /// \p GEP The GEP. The indices contained in the GEP itself are ignored,
   /// instead we use IndexExprs.
   /// \p IndexExprs The expressions for the indices.
-  LLVM_ABI const SCEV *
-  getGEPExpr(GEPOperator *GEP, const SmallVectorImpl<const SCEV *> &IndexExprs);
+  LLVM_ABI const SCEV *getGEPExpr(GEPOperator *GEP,
+                                  ArrayRef<const SCEV *> IndexExprs);
+  LLVM_ABI const SCEV *getGEPExpr(const SCEV *BaseExpr,
+                                  ArrayRef<const SCEV *> IndexExprs,
+                                  Type *SrcElementTy,
+                                  GEPNoWrapFlags NW = GEPNoWrapFlags::none());
   LLVM_ABI const SCEV *getAbsExpr(const SCEV *Op, bool IsNSW);
   LLVM_ABI const SCEV *getMinMaxExpr(SCEVTypes Kind,
                                      SmallVectorImpl<const SCEV *> &Operands);

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -3768,13 +3768,11 @@ ScalarEvolution::getAddRecExpr(SmallVectorImpl<const SCEV *> &Operands,
   return getOrCreateAddRecExpr(Operands, L, Flags);
 }
 
-const SCEV *
-ScalarEvolution::getGEPExpr(GEPOperator *GEP,
-                            const SmallVectorImpl<const SCEV *> &IndexExprs) {
+const SCEV *ScalarEvolution::getGEPExpr(GEPOperator *GEP,
+                                        ArrayRef<const SCEV *> IndexExprs) {
   const SCEV *BaseExpr = getSCEV(GEP->getPointerOperand());
   // getSCEV(Base)->getType() has the same address space as Base->getType()
   // because SCEV::getType() preserves the address space.
-  Type *IntIdxTy = getEffectiveSCEVType(BaseExpr->getType());
   GEPNoWrapFlags NW = GEP->getNoWrapFlags();
   if (NW != GEPNoWrapFlags::none()) {
     // We'd like to propagate flags from the IR to the corresponding SCEV nodes,
@@ -3787,13 +3785,20 @@ ScalarEvolution::getGEPExpr(GEPOperator *GEP,
       NW = GEPNoWrapFlags::none();
   }
 
+  return getGEPExpr(BaseExpr, IndexExprs, GEP->getSourceElementType(), NW);
+}
+
+const SCEV *ScalarEvolution::getGEPExpr(const SCEV *BaseExpr,
+                                        ArrayRef<const SCEV *> IndexExprs,
+                                        Type *SrcElementTy, GEPNoWrapFlags NW) {
   SCEV::NoWrapFlags OffsetWrap = SCEV::FlagAnyWrap;
   if (NW.hasNoUnsignedSignedWrap())
     OffsetWrap = setFlags(OffsetWrap, SCEV::FlagNSW);
   if (NW.hasNoUnsignedWrap())
     OffsetWrap = setFlags(OffsetWrap, SCEV::FlagNUW);
 
-  Type *CurTy = GEP->getType();
+  Type *CurTy = BaseExpr->getType();
+  Type *IntIdxTy = getEffectiveSCEVType(BaseExpr->getType());
   bool FirstIter = true;
   SmallVector<const SCEV *, 4> Offsets;
   for (const SCEV *IndexExpr : IndexExprs) {
@@ -3812,7 +3817,7 @@ ScalarEvolution::getGEPExpr(GEPOperator *GEP,
       if (FirstIter) {
         assert(isa<PointerType>(CurTy) &&
                "The first index of a GEP indexes a pointer");
-        CurTy = GEP->getSourceElementType();
+        CurTy = SrcElementTy;
         FirstIter = false;
       } else {
         CurTy = GetElementPtrInst::getTypeAtIndex(CurTy, (uint64_t)0);