[cfe-commits] r145070 - /cfe/trunk/lib/Lex/Lexer.cpp

[Eli Friedman]

On Tue, Nov 22, 2011 at 10:56 AM, Benjamin Kramer
<benny.kra at googlemail.com> wrote:
> Author: d0k
> Date: Tue Nov 22 12:56:46 2011
> New Revision: 145070
>
> URL: http://llvm.org/viewvc/llvm-project?rev=145070&view=rev
> Log:
> Lexer: Don't throw away the hard work SSE did to find a slash.
>
> We can reuse the information and avoid looping over all the bytes again.

What effect on performance does this change have?

-Eli

> Modified:
>    cfe/trunk/lib/Lex/Lexer.cpp
>
> Modified: cfe/trunk/lib/Lex/Lexer.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Lex/Lexer.cpp?rev=145070&r1=145069&r2=145070&view=diff
> ==============================================================================
> --- cfe/trunk/lib/Lex/Lexer.cpp (original)
> +++ cfe/trunk/lib/Lex/Lexer.cpp Tue Nov 22 12:56:46 2011
> @@ -1916,11 +1916,18 @@
>       if (C == '/') goto FoundSlash;
>
>  #ifdef __SSE2__
> -      __m128i Slashes = _mm_set_epi8('/', '/', '/', '/', '/', '/', '/', '/',
> -                                     '/', '/', '/', '/', '/', '/', '/', '/');
> -      while (CurPtr+16 <= BufferEnd &&
> -             _mm_movemask_epi8(_mm_cmpeq_epi8(*(__m128i*)CurPtr, Slashes)) == 0)
> +      __m128i Slashes = _mm_set1_epi8('/');
> +      while (CurPtr+16 <= BufferEnd) {
> +        int cmp = _mm_movemask_epi8(_mm_cmpeq_epi8(*(__m128i*)CurPtr, Slashes));
> +        if (cmp != 0) {
> +          // Adjust the pointer to the first '/' that was found.
> +          CurPtr += llvm::CountTrailingZeros_32(cmp);
> +          C = *CurPtr++;
> +          assert(C == '/');
> +          goto FoundSlash;
> +        }
>         CurPtr += 16;
> +      }
>  #elif __ALTIVEC__
>       __vector unsigned char Slashes = {
>         '/', '/', '/', '/',  '/', '/', '/', '/',
> @@ -1948,8 +1955,8 @@
>     while (C != '/' && C != '\0')
>       C = *CurPtr++;
>
> -  FoundSlash:
>     if (C == '/') {
> +  FoundSlash:
>       if (CurPtr[-2] == '*')  // We found the final */.  We're done!
>         break;
>
>
>
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