[FFmpeg-devel] [FFmpeg-cvslog] r12171 - trunk/doc/optimization.txt
Michael Niedermayer
michaelni
Thu Feb 21 21:17:50 CET 2008
On Thu, Feb 21, 2008 at 09:10:56PM +0100, Reimar D?ffinger wrote:
> On Thu, Feb 21, 2008 at 09:51:53PM +0200, ?smail D?nmez wrote:
> > > Not asm, but maybe someone is motivated to test this with a up-to-date
> > > gcc on some 32 bit system:
> > > > #include <inttypes.h>
> > > > uint64_t a;
> > > > uint16_t b;
> > > > uint64_t mul(void) {
> > > > return a * b;
> > > > }
> >
> >
> > gcc 4.4 trunk produces :
> >
> > movq _b at GOTPCREL(%rip), %rax
> > movzwl (%rax), %eax
> > movzwl %ax, %edx
> > movq _a at GOTPCREL(%rip), %rax
> > movq (%rax), %rax
> > imulq %rdx, %rax
> > leave
> > ret
>
> I am fairly certain that not even gcc < 3 managed to get that wrong on a
> _64-bit_ system...
my 2.95 doesnt seem to support x86-64
but all the later ones create:
.LFB6:
movzwq b(%rip), %rax
imulq a(%rip), %rax
ret
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
It is dangerous to be right in matters on which the established authorities
are wrong. -- Voltaire
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