[lld] r248052 - COFF: Parallelize Writer::writeSections().

[David Blaikie via llvm-commits]

On Fri, Sep 18, 2015 at 3:07 PM, Rui Ueyama via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: ruiu
> Date: Fri Sep 18 17:07:10 2015
> New Revision: 248052
>
> URL: http://llvm.org/viewvc/llvm-project?rev=248052&view=rev
> Log:
> COFF: Parallelize Writer::writeSections().
>
> Self-hosting took 801 ms on my machine. Of which this function took
> 69 ms. Now it takes 37 ms. That is about 4% overall performance
> improvement.
>
> Modified:
>     lld/trunk/COFF/Writer.cpp
>
> Modified: lld/trunk/COFF/Writer.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/lld/trunk/COFF/Writer.cpp?rev=248052&r1=248051&r2=248052&view=diff
>
> ==============================================================================
> --- lld/trunk/COFF/Writer.cpp (original)
> +++ lld/trunk/COFF/Writer.cpp Fri Sep 18 17:07:10 2015
> @@ -14,6 +14,7 @@
>  #include "SymbolTable.h"
>  #include "Symbols.h"
>  #include "Writer.h"
> +#include "lld/Core/Parallel.h"
>  #include "llvm/ADT/ArrayRef.h"
>  #include "llvm/ADT/DenseMap.h"
>  #include "llvm/ADT/STLExtras.h"
> @@ -708,8 +709,8 @@ void Writer::writeSections() {
>      // ADD instructions).
>      if (Sec->getPermissions() & IMAGE_SCN_CNT_CODE)
>        memset(SecBuf, 0xCC, Sec->getRawSize());
> -    for (Chunk *C : Sec->getChunks())
> -      C->writeTo(SecBuf);
> +    parallel_for_each(Sec->getChunks().begin(), Sec->getChunks().end(),
> +                      [&](Chunk *C) { C->writeTo(SecBuf); });
>

I gather this is safely parallelizable as each Chunk will write to distinct
regions of SecBuf, without ever overlapping/racing?


>    }
>  }
>
>
>
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