[InstSimplify][SVE] Fix SimplifyGEPInst for scalable vector.

[huihuiz]

Summary

Skip folds that rely on DataLayout::getTypeAllocSize(). For scalable
vector, only minimal type alloc size is known at compile-time.

[huihuiz]

take test.ll, run: opt -S -instsimplify test.ll -o -

define <vscale x 4 x <vscale x 4 x i32>*> @getelementptr_2() {
  %ptr = getelementptr <vscale x 4 x i32>, <vscale x 4 x i32>* null, <vscale x 4 x i64> undef
  ret <vscale x 4 x <vscale x 4 x i32>*> %ptr
}

current upstream crash at: llvm/include/llvm/Support/TypeSize.h:126: uint64_t llvm::TypeSize::getFixedSize() const: Assertion `!IsScalable && "Request for a fixed size on a scalable object"' failed.

This patch depends on D74386, otherwise we get another crash at: llvm/lib/IR/Value.cpp:408: void llvm::Value::doRAUW(llvm::Value *, llvm::Value::ReplaceMetadataUses): Assertion `New->getType() == getType() && "replaceAllUses of value with new value of different type!"' failed.

[efriedma]

llvm/test/Transforms/InstSimplify/vscale.ll

14

@getelementptr_1 passes without this patch, right?

22

Please add testcases with a vscale'ed source type that doesn't simplify to a constant.

Please add a testcase like getelementptr <vscale x 4 x i32>, <vscale x 4 x i32>* null, i64 %x (where the return type is a pointer to a vector, rather than a vector of pointers to vectors).

[huihuiz]

Add more test to check the code path, as suggested.

llvm/test/Transforms/InstSimplify/vscale.ll

14

Yes, @getelementptr_1 passes without this patch.

[efriedma]

LGTM

llvm/lib/Analysis/InstructionSimplify.cpp

4085

We should probably consider adding an API to Type to check whether the size of a type is a compile-time constant, so we don't repeat SrcTy->isVectorTy() ? SrcTy->getVectorIsScalable() : false all over the place. I guess that doesn't have to happen here, though.

[huihuiz]

llvm/lib/Analysis/InstructionSimplify.cpp

4085

Thanks Eli for the feedback! I will post a patch for this.

llvm/lib/Analysis/InstructionSimplify.cpp

   if (VectorType *VT = dyn_cast<VectorType>(Ops[0]->getType()))
     GEPTy = VectorType::get(GEPTy, VT->getElementCount());
   else if (VectorType *VT = dyn_cast<VectorType>(Ops[1]->getType()))
     GEPTy = VectorType::get(GEPTy, VT->getElementCount());
 
   if (isa<UndefValue>(Ops[0]))
     return UndefValue::get(GEPTy);
 
+  bool IsScalableVec =
+      SrcTy->isVectorTy() ? SrcTy->getVectorIsScalable() : false;
+
   if (Ops.size() == 2) {
     // getelementptr P, 0 -> P.
     if (match(Ops[1], m_Zero()) && Ops[0]->getType() == GEPTy)
       return Ops[0];
 
     Type *Ty = SrcTy;
-    if (Ty->isSized()) {
+    if (!IsScalableVec && Ty->isSized()) {
       Value *P;
       uint64_t C;
       uint64_t TyAllocSize = Q.DL.getTypeAllocSize(Ty);
       // getelementptr P, N -> P if P points to a type of zero size.
       if (TyAllocSize == 0 && Ops[0]->getType() == GEPTy)
         return Ops[0];
 
       // The following transforms are only safe if the ptrtoint cast

                   m_SDiv(m_Sub(m_Value(P), m_PtrToInt(m_Specific(Ops[0]))),
                          m_SpecificInt(TyAllocSize))))
           if (Value *R = PtrToIntOrZero(P))
             return R;
       }
     }
   }
 
-  if (Q.DL.getTypeAllocSize(LastType) == 1 &&
+  if (!IsScalableVec && Q.DL.getTypeAllocSize(LastType) == 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) {
       APInt BasePtrOffset(IdxWidth, 0);
       Value *StrippedBasePtr =
           Ops[0]->stripAndAccumulateInBoundsConstantOffsets(Q.DL,

llvm/test/Transforms/InstSimplify/vscale.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -instsimplify -verify < %s | FileCheck %s
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Memory Access and Addressing Operations
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+define <vscale x 4 x i32*> @getelementptr_1() {
+; CHECK-LABEL: @getelementptr_1(
+; CHECK-NEXT:    ret <vscale x 4 x i32*> zeroinitializer
+;
+  %ptr = getelementptr i32, <vscale x 4 x i32*> zeroinitializer, <vscale x 4 x i64> undef
+  ret <vscale x 4 x i32*> %ptr
+}
+
+define <vscale x 4 x <vscale x 4 x i32>*> @getelementptr_2() {
+; CHECK-LABEL: @getelementptr_2(
+; CHECK-NEXT:    ret <vscale x 4 x <vscale x 4 x i32>*> zeroinitializer
+;
+  %ptr = getelementptr <vscale x 4 x i32>, <vscale x 4 x i32>* null, <vscale x 4 x i64> undef
+  ret <vscale x 4 x <vscale x 4 x i32>*> %ptr
+}
+