[PATCH] D26014: [ConstantFold] Get the correct vector type when folding a getelementptr instruction with vector indices

[Filipe Cabecinhas via llvm-commits]

Can we have mixed integer and vector indices (langref doesn't seem to
forbid it)? If so, what happens if the first one is an integer, and then
you get a vector of indices?

 Filipe

On Wednesday, 26 October 2016, Davide Italiano via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> davide created this revision.
> davide added reviewers: majnemer, Bigcheese, RKSimon, spatel.
> davide added a subscriber: llvm-commits.
>
> When we constant fold `getelementptr` and the indices are vector, the type
> created is `i64 *` and not `<8 x i64*>` which caseuse an assertion to fire
> in `replaceAllUsesWith`. I think it's OK just checking for the first index
> for the reason pointed out in the comment.
>
>
> https://reviews.llvm.org/D26014
>
> Files:
>   lib/IR/ConstantFold.cpp
>   test/Transforms/InstCombine/gep-vector.ll
>
>
> Index: test/Transforms/InstCombine/gep-vector.ll
> ===================================================================
> --- /dev/null
> +++ test/Transforms/InstCombine/gep-vector.ll
> @@ -0,0 +1,19 @@
> +; RUN: opt -instcombine %s -S | FileCheck %s
> +
> +; CHECK-LABEL: patatino
> +; CHECK-NEXT: ret void
> +define void @patatino() {
> +  %el = getelementptr i64, <8 x i64*> undef, <8 x i64> undef
> +  %gather = call <8 x i64> @llvm.masked.gather.v8i64(<8 x i64*> %el, i32
> 8, <8 x i1> <i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true,
> i1 true>, <8 x i64> undef)
> +  ret void
> +}
> +
> +; CHECK-LABEL: patatino2
> +; CHECK-NEXT: ret void
> +define void @patatino2() {
> +  %el = getelementptr inbounds i64, i64* undef, <8 x i64> undef
> +  %gather = call <8 x i64> @llvm.masked.gather.v8i64(<8 x i64*> %el, i32
> 8, <8 x i1> <i1 true, i1 true, i1 true, i1 true, i1 true, i1 true, i1 true,
> i1 true>, <8 x i64> undef)
> +  ret void
> +}
> +
> +declare <8 x i64> @llvm.masked.gather.v8i64(<8 x i64*>, i32, <8 x i1>, <8
> x i64>)
> Index: lib/IR/ConstantFold.cpp
> ===================================================================
> --- lib/IR/ConstantFold.cpp
> +++ lib/IR/ConstantFold.cpp
> @@ -2062,6 +2062,12 @@
>      Type *GEPTy = PointerType::get(Ty, PtrTy->getAddressSpace());
>      if (VectorType *VT = dyn_cast<VectorType>(C->getType()))
>        GEPTy = VectorType::get(GEPTy, VT->getNumElements());
> +    // When the getelementptr has one of more vector indices, it will
> +    // return a vector of pointers. We guarantee that all the vectors
> +    // in this case will have the same width, so we can just look at
> +    // the first one.
> +    else if (VectorType *VT = dyn_cast<VectorType>(Idxs[0]->getType()))
> +      GEPTy = VectorType::get(GEPTy, VT->getNumElements());
>      return UndefValue::get(GEPTy);
>    }
>
>
>
>

-- 
  F
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