[PATCH] D76655: [InstSimplify][SVE] Minor fix SimplifyGEPInst for scalable vector.

[Huihui Zhang via Phabricator via llvm-commits]

huihuiz updated this revision to Diff 257524.
huihuiz edited the summary of this revision.
huihuiz added a comment.

My initial thought was wrong.
Spent sometime look again, we are nearly impossible to generate incorrect result without the code fixes in this patch.
But comparing a scalable size with a fixed size still doesn't make sense.

E.g., We are comparing scalable type size %offset to a fixed size 'IdxWidth' returned by DataLayout::getIndexSizeInBits

  define <vscale x 1 x i8*> @gep(i8* %a, <vscale x 1 x i32> %offset) {
    %v = getelementptr i8, i8* %a, <vscale x 1 x i32> %offset
    ret <vscale x 1 x i8*> %v
  }

Please help take a look, let me know what you think?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D76655/new/

https://reviews.llvm.org/D76655

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp


Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4094,7 +4094,7 @@
     if (!IsScalableVec && Ty->isSized()) {
       Value *P;
       uint64_t C;
-      uint64_t TyAllocSize = Q.DL.getTypeAllocSize(Ty);
+      uint64_t TyAllocSize = Q.DL.getTypeAllocSize(Ty).getFixedSize();
       // getelementptr P, N -> P if P points to a type of zero size.
       if (TyAllocSize == 0 && Ops[0]->getType() == GEPTy)
         return Ops[0];
@@ -4139,12 +4139,15 @@
     }
   }
 
-  if (!IsScalableVec && Q.DL.getTypeAllocSize(LastType) == 1 &&
+  if (!IsScalableVec && Q.DL.getTypeAllocSize(LastType).getFixedSize() == 1 &&
       all_of(Ops.slice(1).drop_back(1),
              [](Value *Idx) { return match(Idx, m_Zero()); })) {
     unsigned IdxWidth =
         Q.DL.getIndexSizeInBits(Ops[0]->getType()->getPointerAddressSpace());
-    if (Q.DL.getTypeSizeInBits(Ops.back()->getType()) == IdxWidth) {
+    // Skip if offset type size is not a compile-time constant.
+    TypeSize OffsetTypeSize = Q.DL.getTypeSizeInBits(Ops.back()->getType());
+    if (!OffsetTypeSize.isScalable() &&
+        OffsetTypeSize.getFixedSize() == IdxWidth) {
       APInt BasePtrOffset(IdxWidth, 0);
       Value *StrippedBasePtr =
           Ops[0]->stripAndAccumulateInBoundsConstantOffsets(Q.DL,


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