[llvm] r209162 - [ConstantHoisting][X86] Change the cost model to never hoist constants for types larger than i128.

[Quentin Colombet]

Thanks!

-Quentin

On May 19, 2014, at 2:44 PM, Juergen Ributzka <juergen at apple.com> wrote:

> I filed http://llvm.org/bugs/show_bug.cgi?id=19797
> 
> On May 19, 2014, at 2:28 PM, Quentin Colombet <qcolombet at apple.com> wrote:
> 
>> Hi Juergen,
>> 
>> Could you file a PR for the actual issue?
>> 
>> Thanks,
>> -Quentin
>> 
>> On May 19, 2014, at 2:00 PM, Juergen Ributzka <juergen at apple.com> wrote:
>> 
>>> Author: ributzka
>>> Date: Mon May 19 16:00:53 2014
>>> New Revision: 209162
>>> 
>>> URL: http://llvm.org/viewvc/llvm-project?rev=209162&view=rev
>>> Log:
>>> [ConstantHoisting][X86] Change the cost model to never hoist constants for types larger than i128.
>>> 
>>> Currently the X86 backend doesn't support types larger than i128 very well. For
>>> example an i192 multiply will assert in codegen when the 2nd argument is a constant and the constant got hoisted.
>>> 
>>> This fix changes the cost model to never hoist constants for types larger than
>>> i128. Once the codegen issues have been resolved, the cost model can be updated
>>> to allow also larger types.
>>> 
>>> This is related to <rdar://problem/16954938>
>>> 
>>> Modified:
>>>    llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp
>>>    llvm/trunk/test/Transforms/ConstantHoisting/X86/large-immediate.ll
>>> 
>>> Modified: llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp?rev=209162&r1=209161&r2=209162&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp (original)
>>> +++ llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp Mon May 19 16:00:53 2014
>>> @@ -815,6 +815,13 @@ unsigned X86TTI::getIntImmCost(const API
>>>   if (BitSize == 0)
>>>     return ~0U;
>>> 
>>> +  // Never hoist constants larger than 128bit, because this might lead to
>>> +  // incorrect code generation or assertions in codegen.
>>> +  // Fixme: Create a cost model for types larger than i128 once the codegen
>>> +  // issues have been fixed.
>>> +  if (BitSize > 128)
>>> +    return TCC_Free;
>>> +
>>>   if (Imm == 0)
>>>     return TCC_Free;
>>> 
>>> @@ -830,8 +837,10 @@ unsigned X86TTI::getIntImmCost(unsigned
>>>   assert(Ty->isIntegerTy());
>>> 
>>>   unsigned BitSize = Ty->getPrimitiveSizeInBits();
>>> +  // There is no cost model for constants with a bit size of 0. Return TCC_Free
>>> +  // here, so that constant hoisting will ignore this constant.
>>>   if (BitSize == 0)
>>> -    return ~0U;
>>> +    return TCC_Free;
>>> 
>>>   unsigned ImmIdx = ~0U;
>>>   switch (Opcode) {
>>> @@ -892,8 +901,10 @@ unsigned X86TTI::getIntImmCost(Intrinsic
>>>   assert(Ty->isIntegerTy());
>>> 
>>>   unsigned BitSize = Ty->getPrimitiveSizeInBits();
>>> +  // There is no cost model for constants with a bit size of 0. Return TCC_Free
>>> +  // here, so that constant hoisting will ignore this constant.
>>>   if (BitSize == 0)
>>> -    return ~0U;
>>> +    return TCC_Free;
>>> 
>>>   switch (IID) {
>>>   default: return TCC_Free;
>>> 
>>> Modified: llvm/trunk/test/Transforms/ConstantHoisting/X86/large-immediate.ll
>>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/ConstantHoisting/X86/large-immediate.ll?rev=209162&r1=209161&r2=209162&view=diff
>>> ==============================================================================
>>> --- llvm/trunk/test/Transforms/ConstantHoisting/X86/large-immediate.ll (original)
>>> +++ llvm/trunk/test/Transforms/ConstantHoisting/X86/large-immediate.ll Mon May 19 16:00:53 2014
>>> @@ -16,3 +16,12 @@ define i512 @test2(i512 %a) nounwind {
>>>   %2 = ashr i512 %1, 504
>>>   ret i512 %2
>>> }
>>> +
>>> +; Check that we don't hoist constants with a type larger than i128.
>>> +define i196 @test3(i196 %a) nounwind {
>>> +; CHECK-LABEL: test3
>>> +; CHECK-NOT: %const = bitcast i196 2 to i196
>>> +  %1 = mul i196 %a, 2
>>> +  %2 = mul i196 %1, 2
>>> +  ret i196 %2
>>> +}
>>> 
>>> 
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>>> llvm-commits at cs.uiuc.edu
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>> 
> 

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