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

[Evgeny Stupachenko via llvm-commits]

Well, is

 %1 = mul nsw i8 0, %0

binary operator?
It has Zero SCEV.


On Thu, Mar 8, 2018 at 1:57 PM, Philip Reames <listmail at philipreames.com>
wrote:

> 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/Transform
>> s/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/Transfor
>> ms/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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>
>
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