[llvm] 137568e - [InstCombine] Fixed UB in foldCtpop

[David Blaikie via llvm-commits]

Ah, cool - thanks!

On Sun, May 2, 2021 at 1:00 PM Dávid Bolvanský <david.bolvansky at gmail.com>
wrote:

> Yes, it was exposed on msan buildbot - use of uninit. value.
>
> Dňa 2. 5. 2021 o 21:36 užívateľ David Blaikie <dblaikie at gmail.com>
> napísal:
>
> 
> Was this covered by existing tests (but only exposed on some buildbot or
> another configuration that tickled the UB into being more problematic?)?
>
> On Sat, Apr 24, 2021 at 10:44 AM Dávid Bolvanský via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>>
>> Author: Dávid Bolvanský
>> Date: 2021-04-24T19:44:16+02:00
>> New Revision: 137568e5797c33c12d284cc325367ceaddf2441a
>>
>> URL:
>> https://github.com/llvm/llvm-project/commit/137568e5797c33c12d284cc325367ceaddf2441a
>> DIFF:
>> https://github.com/llvm/llvm-project/commit/137568e5797c33c12d284cc325367ceaddf2441a.diff
>>
>> LOG: [InstCombine] Fixed UB in foldCtpop
>>
>> Added:
>>
>>
>> Modified:
>>     llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
>>
>> Removed:
>>
>>
>>
>>
>> ################################################################################
>> diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
>> b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
>> index 378682b7b9cd..72008dfa3b28 100644
>> --- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
>> +++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
>> @@ -497,7 +497,7 @@ static Instruction *foldCtpop(IntrinsicInst &II,
>> InstCombinerImpl &IC) {
>>    Type *Ty = II.getType();
>>    unsigned BitWidth = Ty->getScalarSizeInBits();
>>    Value *Op0 = II.getArgOperand(0);
>> -  Value *X;
>> +  Value *X, *Y;
>>
>>    // ctpop(bitreverse(x)) -> ctpop(x)
>>    // ctpop(bswap(x)) -> ctpop(x)
>> @@ -505,8 +505,9 @@ static Instruction *foldCtpop(IntrinsicInst &II,
>> InstCombinerImpl &IC) {
>>      return IC.replaceOperand(II, 0, X);
>>
>>    // ctpop(rot(x)) -> ctpop(x)
>> -  if (match(Op0, m_FShl(m_Value(X), m_Specific(X), m_Value())) ||
>> -      match(Op0, m_FShr(m_Value(X), m_Specific(X), m_Value())))
>> +  if ((match(Op0, m_FShl(m_Value(X), m_Value(Y), m_Value())) ||
>> +       match(Op0, m_FShr(m_Value(X), m_Value(Y), m_Value()))) &&
>> +      X == Y)
>>      return IC.replaceOperand(II, 0, X);
>>
>>    // ctpop(x | -x) -> bitwidth - cttz(x, false)
>>
>>
>>
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>
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