rawhide report: 20050510 changes

[Nils Philippsen]

On Tue, 2005-05-10 at 11:02 -0400, Jakub Jelinek wrote:
> On Tue, May 10, 2005 at 04:53:55PM +0200, Nils Philippsen wrote:
> > > c) if you use -msse2 in CFLAGS for all files, you can't run the latest
> > >    GIMP on e.g. Pentium2, or pre-x86_64 AMD chips.
> > >    -msse2 should be ONLY used on sources that have SSE/SSE2 stuff in it,
> > >    and GIMP should make sure that no routine from those sources will be
> > >    ever called on pre-SSE2 chips
> > 
> > According to the gcc man page, you need to use "-mfpmath=sse" if you
> > want to get SSE/SSE2 instructions generated from FP code. As I
> 
> No.  -msse resp. -msse2 says that SSE resp. SSE2 instructions are available
> and can be used.  So, with -msse2 you can use SSE2 builtins, you can
> use those regs in __asm statement clobbers/regs and GCC if it decides
> it is worthwhile can use the SSE2 registers/instructions (say with
> autovectorization, or with high register preasure to move data around,
> etc.).
> -mfpmath=sse uses the SSE2 unit for float/double arithmetics.
> 
> If the only place that you want to enable -msse2 for are the clobber
> lists of __asm statements, then perhaps best would be to conditionalize
> them:
> __asm ("something" : ... : ... :
> #ifdef __SSE2__
> "xmm0", "xmm1"
> #endif
> );
> etc., because without -msse2 (resp. -msse (__SSE__ macro)), the registers
> are not known to the compiler, so there is no point to tell the compiler
> about them.

Ahh. If I understand you correctly, given that the various asm optimized
functions are in separate source files, it should be ensured that 
-mmmx/sse/sse2/3dnow are used only for the relevant source files?

Nils
-- 
     Nils Philippsen    /    Red Hat    /    nphilipp at redhat.com
"They that can give up essential liberty to obtain a little temporary
 safety deserve neither liberty nor safety."     -- B. Franklin, 1759
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