Reapply [ConstantFold] Drop gep of gep fold entirely (#95126)

Reapplying without changes. The flang+openmp buildbot failure
should be addressed by https://github.com/llvm/llvm-project/pull/94541.

-----

This is a followup to https://github.com/llvm/llvm-project/pull/93823
and drops the DataLayout-unaware GEP of GEP fold entirely. All cases are
now left to the DataLayout-aware constant folder, which will fold
everything to a single i8 GEP.

We didn't have any test coverage for this fold in LLVM, but some Clang
tests change.

4 files changed, 4 insertions, 39 deletions

diff --git a/llvm/include/llvm/IR/ConstantFold.h b/llvm/include/llvm/IR/ConstantFold.h
index 9b3c8a0..42043d3 100644
--- a/llvm/include/llvm/IR/ConstantFold.h
+++ b/llvm/include/llvm/IR/ConstantFold.h
@@ -52,7 +52,7 @@ namespace llvm {
                                           Constant *V2);
   Constant *ConstantFoldCompareInstruction(CmpInst::Predicate Predicate,
                                            Constant *C1, Constant *C2);
-  Constant *ConstantFoldGetElementPtr(Type *Ty, Constant *C, bool InBounds,
+  Constant *ConstantFoldGetElementPtr(Type *Ty, Constant *C,
                                       std::optional<ConstantRange> InRange,
                                       ArrayRef<Value *> Idxs);
 } // End llvm namespace
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 8b2aa6b..0089586 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5068,9 +5068,8 @@ static Value *simplifyGEPInst(Type *SrcTy, Value *Ptr,
     return nullptr;
 
   if (!ConstantExpr::isSupportedGetElementPtr(SrcTy))
-    // TODO(gep_nowrap): Pass on the whole GEPNoWrapFlags.
-    return ConstantFoldGetElementPtr(SrcTy, cast<Constant>(Ptr),
-                                     NW.isInBounds(), std::nullopt, Indices);
+    return ConstantFoldGetElementPtr(SrcTy, cast<Constant>(Ptr), std::nullopt,
+                                     Indices);
 
   auto *CE =
       ConstantExpr::getGetElementPtr(SrcTy, cast<Constant>(Ptr), Indices, NW);
diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 77a8336..34bcf36 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1404,35 +1404,7 @@ Constant *llvm::ConstantFoldCompareInstruction(CmpInst::Predicate Predicate,
   return nullptr;
 }
 
-// Combine Indices - If the source pointer to this getelementptr instruction
-// is a getelementptr instruction, combine the indices of the two
-// getelementptr instructions into a single instruction.
-static Constant *foldGEPOfGEP(GEPOperator *GEP, Type *PointeeTy, bool InBounds,
-                              ArrayRef<Value *> Idxs) {
-  if (PointeeTy != GEP->getResultElementType())
-    return nullptr;
-
-  // Leave inrange handling to DL-aware constant folding.
-  if (GEP->getInRange())
-    return nullptr;
-
-  // Only handle simple case with leading zero index. We cannot perform an
-  // actual addition as we don't know the correct index type size to use.
-  Constant *Idx0 = cast<Constant>(Idxs[0]);
-  if (!Idx0->isNullValue())
-    return nullptr;
-
-  SmallVector<Value*, 16> NewIndices;
-  NewIndices.reserve(Idxs.size() + GEP->getNumIndices());
-  NewIndices.append(GEP->idx_begin(), GEP->idx_end());
-  NewIndices.append(Idxs.begin() + 1, Idxs.end());
-  return ConstantExpr::getGetElementPtr(
-      GEP->getSourceElementType(), cast<Constant>(GEP->getPointerOperand()),
-      NewIndices, InBounds && GEP->isInBounds());
-}
-
 Constant *llvm::ConstantFoldGetElementPtr(Type *PointeeTy, Constant *C,
-                                          bool InBounds,
                                           std::optional<ConstantRange> InRange,
                                           ArrayRef<Value *> Idxs) {
   if (Idxs.empty()) return C;
@@ -1462,10 +1434,5 @@ Constant *llvm::ConstantFoldGetElementPtr(Type *PointeeTy, Constant *C,
                      cast<VectorType>(GEPTy)->getElementCount(), C)
                : C;
 
-  if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C))
-    if (auto *GEP = dyn_cast<GEPOperator>(CE))
-      if (Constant *C = foldGEPOfGEP(GEP, PointeeTy, InBounds, Idxs))
-        return C;
-
   return nullptr;
 }
diff --git a/llvm/lib/IR/Constants.cpp b/llvm/lib/IR/Constants.cpp
index a76be44..d079073 100644
--- a/llvm/lib/IR/Constants.cpp
+++ b/llvm/lib/IR/Constants.cpp
@@ -2438,8 +2438,7 @@ Constant *ConstantExpr::getGetElementPtr(Type *Ty, Constant *C,
   assert(Ty && "Must specify element type");
   assert(isSupportedGetElementPtr(Ty) && "Element type is unsupported!");
 
-  if (Constant *FC =
-          ConstantFoldGetElementPtr(Ty, C, NW.isInBounds(), InRange, Idxs))
+  if (Constant *FC = ConstantFoldGetElementPtr(Ty, C, InRange, Idxs))
     return FC; // Fold a few common cases.
 
   assert(GetElementPtrInst::getIndexedType(Ty, Idxs) && "GEP indices invalid!");