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gsdx: try to ask GCC to generate not dumb code 

Unfortunately it requires at least GCC6. If a nice guy can check the generated code on GCC6.
I don't know clang status.

Here the only example, I have found on the web
https://developers.redhat.com/blog/2016/02/25/new-asm-flags-feature-for-x86-in-gcc-6/

Current generated code in GSTextureCache::SourceMap::Add

    38b3:	bsf    eax,esi
    38b6:	add    esp,0x10
    38b9:	test   esi,esi
    38bb:	jne    387e <GSTextureCache::SourceMap::Add(GSTextureCache::Source*, GIFRegTEX0 const&, GSOffset*)+0x6e>

BSF already set the Z flag when input (esi) is 0. So it would be better
to not put a silly add before the jump and to skip the test operation.
This commit is contained in:
Gregory Hainaut 2017-01-11 21:25:09 +01:00
parent 1fbee92044
commit 8cf3a83dd7
1 changed files with 9 additions and 3 deletions
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12
plugins/GSdx/stdafx.h
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@ -391,11 +391,17 @@ using namespace stdext;
// http://svn.reactos.org/svn/reactos/trunk/reactos/include/crt/mingw32/intrin_x86.h?view=markup // http://svn.reactos.org/svn/reactos/trunk/reactos/include/crt/mingw32/intrin_x86.h?view=markup
__forceinline unsigned char _BitScanForward(unsigned long* const Index, const unsigned long Mask) __forceinline int _BitScanForward(unsigned long* const Index, const unsigned long Mask)
{ {
__asm__("bsfl %k[Mask], %k[Index]" : [Index] "=r" (*Index) : [Mask] "mr" (Mask)); #if defined(__GCC_ASM_FLAG_OUTPUTS__) && 0
// Need GCC6 to test the code validity
int flag;
__asm__("bsfl %k[Mask], %k[Index]" : [Index] "=r" (*Index), "=@ccz" (flag) : [Mask] "mr" (Mask));
return flag;
#else
__asm__("bsfl %k[Mask], %k[Index]" : [Index] "=r" (*Index) : [Mask] "mr" (Mask) : "cc");
return Mask ? 1 : 0; return Mask ? 1 : 0;
#endif
} }
#ifdef __GNUC__ #ifdef __GNUC__