[llvm] r326861 - Add early exit on reassociation of 0 expression.

[Philip Reames via llvm-commits]

Huh?  Zero is not a binary operator.  So how'd it get here?  This patch 
looks wrong or at least incomplete.

Philip


On 03/06/2018 06:17 PM, Evgeny Stupachenko via llvm-commits wrote:
> Author: evstupac
> Date: Tue Mar  6 18:17:08 2018
> New Revision: 326861
>
> URL: http://llvm.org/viewvc/llvm-project?rev=326861&view=rev
> Log:
> Add early exit on reassociation of 0 expression.
>
> Summary:
>
> Before the patch a try to reassociate ((v * 16) * 0) * 1 fall into infinite loop
>
> Reviewers: pankajchawla
>
> Differential Revision: http://reviews.llvm.org/D41467
>
> From: Evgeny Stupachenko <evstupac at gmail.com>
>                           <evgeny.v.stupachenko at intel.com>
>
> Added:
>      llvm/trunk/test/Transforms/NaryReassociate/pr35710.ll
> Modified:
>      llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp?rev=326861&r1=326860&r2=326861&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp Tue Mar  6 18:17:08 2018
> @@ -429,6 +429,9 @@ NaryReassociatePass::tryReassociateGEPAt
>   
>   Instruction *NaryReassociatePass::tryReassociateBinaryOp(BinaryOperator *I) {
>     Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
> +  // There is no need to reassociate 0.
> +  if (SE->getSCEV(I)->isZero())
> +    return nullptr;
>     if (auto *NewI = tryReassociateBinaryOp(LHS, RHS, I))
>       return NewI;
>     if (auto *NewI = tryReassociateBinaryOp(RHS, LHS, I))
>
> Added: llvm/trunk/test/Transforms/NaryReassociate/pr35710.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/NaryReassociate/pr35710.ll?rev=326861&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/NaryReassociate/pr35710.ll (added)
> +++ llvm/trunk/test/Transforms/NaryReassociate/pr35710.ll Tue Mar  6 18:17:08 2018
> @@ -0,0 +1,19 @@
> +; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
> +; RUN: opt < %s -nary-reassociate -S | FileCheck %s
> +
> +; The test check that compilation does not fall into infinite loop.
> +
> +define i8 @foo(i8 %v) local_unnamed_addr #0 {
> +; CHECK-LABEL: @foo(
> +; CHECK-NEXT:  region.0:
> +; CHECK-NEXT:    [[TMP0:%.*]] = mul nsw i8 16, [[V:%.*]]
> +; CHECK-NEXT:    [[TMP1:%.*]] = mul nsw i8 0, [[TMP0]]
> +; CHECK-NEXT:    [[TMP2:%.*]] = mul nsw i8 1, [[TMP1]]
> +; CHECK-NEXT:    ret i8 [[TMP2]]
> +;
> +region.0:
> +  %0 = mul nsw i8 16, %v
> +  %1 = mul nsw i8 0, %0
> +  %2 = mul nsw i8 1, %1
> +  ret i8 %2
> +}
>
>
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