[PATCH] D24088: Create a getelementptr instead of sub expr for ValueOffsetPair if the value is a pointer

[Wei Mi via llvm-commits]

Hi Sanjoy,

Could you take a look? The patch is to fix a compiler crash.

Thanks,
Wei.

On Wed, Aug 31, 2016 at 9:56 AM, Wei Mi <wmi at google.com> wrote:
> wmi created this revision.
> wmi added a reviewer: sanjoy.
> wmi added a subscriber: llvm-commits.
> wmi set the repository for this revision to rL LLVM.
> Herald added a subscriber: mzolotukhin.
>
> This patch is to fix https://llvm.org/bugs/show_bug.cgi?id=30213
>
> When composing an expr for ValueOffsetPair, if the value is of pointer type, we can only create a getelementptr instead of sub expr.
>
>
>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D24088
>
> Files:
>   lib/Analysis/ScalarEvolutionExpander.cpp
>   test/Analysis/ScalarEvolution/pr30213.ll
>
> Index: test/Analysis/ScalarEvolution/pr30213.ll
> ===================================================================
> --- test/Analysis/ScalarEvolution/pr30213.ll
> +++ test/Analysis/ScalarEvolution/pr30213.ll
> @@ -0,0 +1,35 @@
> +; PR30213
> +; RUN: opt < %s -loop-reduce -S | FileCheck %s
> +
> +; CHECK: %ptr4.ptr1 = select i1 %cmp.i, i8* %ptr4, i8* %ptr1
> +; CHECK-NEXT: %scevgep = getelementptr i8, i8* %ptr4.ptr1, i32 1
> +; CHECK-NEXT: br label %while.cond.i
> +
> +target datalayout = "e-m:o-p:32:32-f64:32:64-f80:128-n8:16:32-S128"
> +target triple = "i386-apple-macosx10.12.0"
> +
> +; Function Attrs: nounwind optsize ssp
> +define void @Foo() {
> +entry:
> +  switch i2 undef, label %sw.epilog102 [
> +    i2 -2, label %sw.bb28
> +  ]
> +
> +sw.bb28:                                          ; preds = %entry
> +  %0 = load i8*, i8** undef, align 2
> +  %ptr1 = getelementptr inbounds i8, i8* undef, i32 -1
> +  %ptr4 = getelementptr inbounds i8, i8* %0, i32 -1
> +  %cmp.i = icmp ult i8* undef, %0
> +  %ptr4.ptr1 = select i1 %cmp.i, i8* %ptr4, i8* %ptr1
> +  br label %while.cond.i
> +
> +while.cond.i:                                     ; preds = %while.cond.i, %sw.bb28
> +  %currPtr.1.i = phi i8* [ %incdec.ptr.i, %while.cond.i ], [ %ptr4.ptr1, %sw.bb28 ]
> +  %incdec.ptr.i = getelementptr inbounds i8, i8* %currPtr.1.i, i32 1
> +  %1 = load i8, i8* %incdec.ptr.i, align 1
> +  br label %while.cond.i
> +
> +sw.epilog102:                                     ; preds = %entry
> +  unreachable
> +}
> +
> Index: lib/Analysis/ScalarEvolutionExpander.cpp
> ===================================================================
> --- lib/Analysis/ScalarEvolutionExpander.cpp
> +++ lib/Analysis/ScalarEvolutionExpander.cpp
> @@ -1703,9 +1703,17 @@
>
>    if (!V)
>      V = visit(S);
> -  else if (VO.second)
> -    V = Builder.CreateSub(V, VO.second);
> -
> +  else if (VO.second) {
> +    if (V->getType()->isPointerTy()) {
> +      Type *Ety = V->getType()->getPointerElementType();
> +      int64_t Offset = VO.second->getSExtValue();
> +      ConstantInt *Idx = ConstantInt::getSigned(
> +          VO.second->getType(), -Offset * 8 / Ety->getScalarSizeInBits());
> +      V = Builder.CreateGEP(Ety, V, Idx, "scevgep");
> +    } else {
> +      V = Builder.CreateSub(V, VO.second);
> +    }
> +  }
>    // Remember the expanded value for this SCEV at this location.
>    //
>    // This is independent of PostIncLoops. The mapped value simply materializes
>
>