[llvm] r270671 - [FunctionAttrs] Volatile loads should disable readonly

[David Majnemer via llvm-commits]

Not that I know of.

On Wed, May 25, 2016 at 10:07 AM, Sean Silva <chisophugis at gmail.com> wrote:

> This is scary. Was this a recent regression?
>
> On Tue, May 24, 2016 at 10:53 PM, David Majnemer via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: majnemer
>> Date: Wed May 25 00:53:04 2016
>> New Revision: 270671
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=270671&view=rev
>> Log:
>> [FunctionAttrs] Volatile loads should disable readonly
>>
>> A volatile load has side effects beyond what callers expect readonly to
>> signify.  For example, it is not safe to reorder two function calls
>> which each perform a volatile load to the same memory location.
>>
>> Modified:
>>     llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp
>>     llvm/trunk/test/Transforms/FunctionAttrs/readattrs.ll
>>
>> Modified: llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp?rev=270671&r1=270670&r2=270671&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp (original)
>> +++ llvm/trunk/lib/Transforms/IPO/FunctionAttrs.cpp Wed May 25 00:53:04
>> 2016
>> @@ -463,6 +463,11 @@ determinePointerReadAttrs(Argument *A,
>>      }
>>
>>      case Instruction::Load:
>> +      // A volatile load has side effects beyond what readonly can be
>> relied
>> +      // upon.
>> +      if (cast<LoadInst>(I)->isVolatile())
>> +        return Attribute::None;
>> +
>>        IsRead = true;
>>        break;
>>
>>
>> Modified: llvm/trunk/test/Transforms/FunctionAttrs/readattrs.ll
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/FunctionAttrs/readattrs.ll?rev=270671&r1=270670&r2=270671&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/test/Transforms/FunctionAttrs/readattrs.ll (original)
>> +++ llvm/trunk/test/Transforms/FunctionAttrs/readattrs.ll Wed May 25
>> 00:53:04 2016
>> @@ -104,3 +104,11 @@ define <4 x i32> @test12_2(<4 x i32*> %p
>>    %res = call <4 x i32> @test12_1(<4 x i32*> %ptrs)
>>    ret <4 x i32> %res
>>  }
>> +
>> +; CHECK: define i32 @volatile_load(
>> +; CHECK-NOT: readonly
>> +; CHECK: ret
>> +define i32 @volatile_load(i32* %p) {
>> +  %load = load volatile i32, i32* %p
>> +  ret i32 %load
>> +}
>>
>>
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>
>
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