Kristian Poul Herkild wrote:
Robert Crawford wrote:
On Sun December 4 2005 4:11 am, Kristian Poul Herkild wrote:
-mfpmath=sse is not a good idea, the consensus is it actually lowers
performance. -msse -mmmx -m3dnow are redundant (implied by
-march=athlon-xp), and should be removed from your cflags line, but
SHOULD be placed in your USE= line, wthout the - sign, like this:
USE="mmx 3dnow sse"
If you use gcc-3.4.4, these flags should work fine (I've used them
for a long time- no problems).
CFLAGS="-march=athlon-xp -O3 -pipe -fomit-frame-pointer -fweb
-ftracer -fprefetch-loop-arrays -ffast-math -falign-functions=64
-fno-ident"
CXXFLAGS="${CFLAGS} -fvisibility-inlines-hidden"
Hmm... according to this thread
http://forums.gentoo.org/viewtopic.php?t=43648 and the GCC manual
-march does not imply -mmx -msse -m3dnow, nor does it imply
mfpmath=sse. I know of no consensus of -mfpmath=sse lowering
performance. Actually, I only know of the opposite from the
LFS-community as well as Gentoo Wiki.
I don't want to start a flamewar on this, so if you have other and
more correct information than me, then please share it :)
-Kristian Poul Herkild
Straight from the source ../gcc-3.4.4/gcc/config/i386/i386.c
{"athlon-xp", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW
| PTA_3DNOW_A | PTA_SSE}
includes mmx, sse, 3dnow and sse2 support making explicit delcarations
in cflags redundant.
and the others...
{"i386", PROCESSOR_I386, 0},
{"i486", PROCESSOR_I486, 0},
{"i586", PROCESSOR_PENTIUM, 0},
{"pentium", PROCESSOR_PENTIUM, 0},
{"pentium-mmx", PROCESSOR_PENTIUM, PTA_MMX},
{"winchip-c6", PROCESSOR_I486, PTA_MMX},
{"winchip2", PROCESSOR_I486, PTA_MMX | PTA_3DNOW},
{"c3", PROCESSOR_I486, PTA_MMX | PTA_3DNOW},
{"c3-2", PROCESSOR_PENTIUMPRO, PTA_MMX | PTA_PREFETCH_SSE |
PTA_SSE},
{"i686", PROCESSOR_PENTIUMPRO, 0},
{"pentiumpro", PROCESSOR_PENTIUMPRO, 0},
{"pentium2", PROCESSOR_PENTIUMPRO, PTA_MMX},
{"pentium3", PROCESSOR_PENTIUMPRO, PTA_MMX | PTA_SSE |
PTA_PREFETCH_SSE},
{"pentium3m", PROCESSOR_PENTIUMPRO, PTA_MMX | PTA_SSE |
PTA_PREFETCH_SSE},
{"pentium-m", PROCESSOR_PENTIUMPRO, PTA_MMX | PTA_SSE |
PTA_PREFETCH_SSE | PTA_SSE2},
{"pentium4", PROCESSOR_PENTIUM4, PTA_SSE | PTA_SSE2 | PTA_MMX |
PTA_PREFETCH_SSE},
{"pentium4m", PROCESSOR_PENTIUM4, PTA_SSE | PTA_SSE2 | PTA_MMX |
PTA_PREFETCH_SSE},
{"prescott", PROCESSOR_PENTIUM4, PTA_SSE | PTA_SSE2 | PTA_SSE3 |
PTA_MMX | PTA_PREFETCH_SSE},
{"nocona", PROCESSOR_PENTIUM4, PTA_SSE | PTA_SSE2 | PTA_SSE3 |
PTA_64BIT | PTA_MMX | PTA_PREFETCH_SSE},
{"k6", PROCESSOR_K6, PTA_MMX},
{"k6-2", PROCESSOR_K6, PTA_MMX | PTA_3DNOW},
{"k6-3", PROCESSOR_K6, PTA_MMX | PTA_3DNOW},
{"athlon", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW
| PTA_3DNOW_A},
{"athlon-tbird", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE
| PTA_3DNOW | PTA_3DNOW_A},
{"athlon-4", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE |
PTA_3DNOW
| PTA_3DNOW_A | PTA_SSE},
{"athlon-xp", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE |
PTA_3DNOW
| PTA_3DNOW_A | PTA_SSE},
{"athlon-mp", PROCESSOR_ATHLON, PTA_MMX | PTA_PREFETCH_SSE |
PTA_3DNOW
| PTA_3DNOW_A | PTA_SSE},
{"x86-64", PROCESSOR_K8, PTA_MMX | PTA_PREFETCH_SSE | PTA_64BIT
| PTA_SSE | PTA_SSE2 },
{"k8", PROCESSOR_K8, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW |
PTA_64BIT
| PTA_3DNOW_A | PTA_SSE | PTA_SSE2},
{"opteron", PROCESSOR_K8, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW
| PTA_64BIT
| PTA_3DNOW_A | PTA_SSE | PTA_SSE2},
{"athlon64", PROCESSOR_K8, PTA_MMX | PTA_PREFETCH_SSE | PTA_3DNOW
| PTA_64BIT
| PTA_3DNOW_A | PTA_SSE | PTA_SSE2}
cheers,
chris
