[llvm] r258149 - Use larger write sizes for MCFillFragment.

[Pete Cooper via llvm-commits]

> On Jan 19, 2016, at 10:04 AM, Rafael Espíndola via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> I just realized I could write the test as attached, but it is probably
> still not worth it.
Yeah, thats an interesting stress test for sure, but you’d probably break some particularly constrained devices like raspberry PIs or something like that.

Pete
> 
> Cheers,
> Rafael
> 
> On 19 January 2016 at 12:47, Rafael Espindola via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>> Author: rafael
>> Date: Tue Jan 19 11:47:48 2016
>> New Revision: 258149
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=258149&view=rev
>> Log:
>> Use larger write sizes for MCFillFragment.
>> 
>> This brings the pr26208 testcase down to 3.2 seconds. Not checking it in
>> since it does create a 4GB .o file.
>> 
>> Modified:
>>    llvm/trunk/lib/MC/MCAssembler.cpp
>> 
>> Modified: llvm/trunk/lib/MC/MCAssembler.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCAssembler.cpp?rev=258149&r1=258148&r2=258149&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/MC/MCAssembler.cpp (original)
>> +++ llvm/trunk/lib/MC/MCAssembler.cpp Tue Jan 19 11:47:48 2016
>> @@ -488,9 +488,20 @@ static void writeFragment(const MCAssemb
>>   case MCFragment::FT_Fill: {
>>     ++stats::EmittedFillFragments;
>>     const MCFillFragment &FF = cast<MCFillFragment>(F);
>> +    uint8_t V = FF.getValue();
>> +    const unsigned MaxChunkSize = 16;
>> +    char Data[MaxChunkSize];
>> +    memcpy(Data, &V, 1);
>> +    for (unsigned I = 1; I < MaxChunkSize; ++I)
>> +      Data[I] = Data[0];
>> 
>> -    for (uint64_t I = 0, E = FF.getSize(); I != E; ++I)
>> -      OW->write8(FF.getValue());
>> +    uint64_t Size = FF.getSize();
>> +    for (unsigned ChunkSize = MaxChunkSize; ChunkSize; ChunkSize /= 2) {
>> +      StringRef Ref(Data, ChunkSize);
>> +      for (uint64_t I = 0, E = Size / ChunkSize; I != E; ++I)
>> +        OW->writeBytes(Ref);
>> +      Size = Size % ChunkSize;
>> +    }
>>     break;
>>   }
>> 
>> 
>> 
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