[llvm] r204739 - [X86TTI] Make constant base pointers for getElementPtr opaque.

[Juergen Ributzka]

Add comments and test case in r205468.

On Mar 31, 2014, at 4:13 PM, Eric Christopher <echristo at gmail.com> wrote:

> Testcase? Comment? Anything?
> 
> -eric
> 
> On Tue, Mar 25, 2014 at 11:01 AM, Juergen Ributzka <juergen at apple.com> wrote:
>> Author: ributzka
>> Date: Tue Mar 25 13:01:25 2014
>> New Revision: 204739
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=204739&view=rev
>> Log:
>> [X86TTI] Make constant base pointers for getElementPtr opaque.
>> 
>> If getElementPtr uses a constant as base pointer, then make the constant opaque.
>> This prevents constant folding it with the offset. The offset can usually be
>> encoded in the load/store instruction itself and the base address doesn't have
>> to be rematerialized several times.
>> 
>> Modified:
>>    llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp
>> 
>> Modified: llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp?rev=204739&r1=204738&r2=204739&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp (original)
>> +++ llvm/trunk/lib/Target/X86/X86TargetTransformInfo.cpp Tue Mar 25 13:01:25 2014
>> @@ -798,8 +798,9 @@ unsigned X86TTI::getIntImmCost(unsigned
>>   switch (Opcode) {
>>   default: return TCC_Free;
>>   case Instruction::GetElementPtr:
>> -    if (Idx != 0)
>> -      return TCC_Free;
>> +    if (Idx == 0)
>> +      return 2 * TCC_Basic;
>> +    return TCC_Free;
>>   case Instruction::Store:
>>     ImmIdx = 0;
>>     break;
>> 
>> 
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