[llvm] r299658 - [InstCombine] Fix a case where we weren't checking that an instruction had a single use resulting in extra instructions being created.

[Craig Topper via llvm-commits]

I'll work on one. My real objective was to remove this code outright
because it should have been dead because its equivalent to transformations
done by SimplifyDemandedInstructionBits. I did remove it in r299337, but
that broke the tsan buildbot so I had to revert it while I figured out what
was going on. What I discovered was that this code was duplicating
instructions and thus firing when SimplifyDemandedInstructionBits wasn't.
So I fixed the duplication and the tsan bot failure. I figured removing the
duplication first was an easier way to explain the tsan change. Now I plan
to go back to removing it completely.

~Craig

On Thu, Apr 6, 2017 at 10:53 AM, Friedman, Eli <efriedma at codeaurora.org>
wrote:

> On 4/6/2017 9:42 AM, Craig Topper via llvm-commits wrote:
>
>> Author: ctopper
>> Date: Thu Apr  6 11:42:46 2017
>> New Revision: 299658
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=299658&view=rev
>> Log:
>> [InstCombine] Fix a case where we weren't checking that an instruction
>> had a single use resulting in extra instructions being created.
>>
>
> Testcase?
>
> -Eli
>
>
>> Modified:
>>      llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
>>
>> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transform
>> s/InstCombine/InstCombineAndOrXor.cpp?rev=299658&r1=299657&
>> r2=299658&view=diff
>> ============================================================
>> ==================
>> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
>> (original)
>> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Thu
>> Apr  6 11:42:46 2017
>> @@ -1332,18 +1332,21 @@ Instruction *InstCombiner::visitAnd(Bina
>>           // ((A & N) + B) & AndRHS -> (A + B) & AndRHS iff N&AndRHS ==
>> AndRHS.
>>           // ((A | N) + B) & AndRHS -> (A + B) & AndRHS iff N&AndRHS == 0
>>           // ((A ^ N) + B) & AndRHS -> (A + B) & AndRHS iff N&AndRHS == 0
>> -        if (Value *V = FoldLogicalPlusAnd(Op0LHS, Op0RHS, AndRHS, false,
>> I))
>> -          return BinaryOperator::CreateAnd(V, AndRHS);
>> -        if (Value *V = FoldLogicalPlusAnd(Op0RHS, Op0LHS, AndRHS, false,
>> I))
>> -          return BinaryOperator::CreateAnd(V, AndRHS);  // Add commutes
>> +        if (Op0I->hasOneUse()) {
>> +          if (Value *V = FoldLogicalPlusAnd(Op0LHS, Op0RHS, AndRHS,
>> false, I))
>> +            return BinaryOperator::CreateAnd(V, AndRHS);
>> +          if (Value *V = FoldLogicalPlusAnd(Op0RHS, Op0LHS, AndRHS,
>> false, I))
>> +            return BinaryOperator::CreateAnd(V, AndRHS);  // Add commutes
>> +        }
>>           break;
>>           case Instruction::Sub:
>>           // ((A & N) - B) & AndRHS -> (A - B) & AndRHS iff N&AndRHS ==
>> AndRHS.
>>           // ((A | N) - B) & AndRHS -> (A - B) & AndRHS iff N&AndRHS == 0
>>           // ((A ^ N) - B) & AndRHS -> (A - B) & AndRHS iff N&AndRHS == 0
>> -        if (Value *V = FoldLogicalPlusAnd(Op0LHS, Op0RHS, AndRHS, true,
>> I))
>> -          return BinaryOperator::CreateAnd(V, AndRHS);
>> +        if (Op0I->hasOneUse())
>> +          if (Value *V = FoldLogicalPlusAnd(Op0LHS, Op0RHS, AndRHS,
>> true, I))
>> +            return BinaryOperator::CreateAnd(V, AndRHS);
>>             // -x & 1 -> x & 1
>>           if (AndRHSMask == 1 && match(Op0LHS, m_Zero()))
>>
>>
>> _______________________________________________
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>> llvm-commits at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>>
>
>
> --
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
> Foundation Collaborative Project
>
>
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