------- Comment #6 from michaelni at gmx dot at 2008-03-22 02:15 -------
As Uros has "challenged me to beat performance of gcc-4.4 generated code by
hand-crafted assembly using the example of PR 21395" heres my entry, sadly i
only have gcc-4.3 compiled ATM for comparission but 4.3 generates better code
than 4.4 so i guess thats ok its inner loop is:
.L23:
movq (%ecx,%eax,2), %mm0
psubw (%edx,%eax,2), %mm0
addl $4, %eax
cmpl %eax, %ebx
movq %mm0, %mm1
psraw $15, %mm0
pxor %mm0, %mm1
psubw %mm0, %mm1
movq %mm1, %mm0
punpcklwd %mm1, %mm1
punpckhwd %mm3, %mm0
psrad $16, %mm1
paddd %mm0, %mm1
paddd %mm1, %mm2
movq %mm2, -24(%ebp)
jg .L23
Its better because the psraw doesnt depend on the previous movq result.
Now heres my code (this is naivly written and not unrolled or hand scheduled,
it also uses hardcoded registers, so i suspect it can be improved further ...)
int SimpleBlockDiff::Diff ()
{
#ifdef __MMX__
int sum;
int x1b=-2*xl;
int ylb= yl;
asm volatile(
"xorl %%edx, %%edx \n\t"
"pcmpeqw %%mm6, %%mm6 \n\t"
"pxor %%mm7, %%mm7 \n\t"
"psrlw $15, %%mm6 \n\t"
"1: \n\t"
"movl (%1, %%edx, 4), %%eax \n\t"
"movl (%2, %%edx, 4), %%esi \n\t"
"movl %3, %%ecx \n\t"
"subl %%ecx, %%eax \n\t"
"subl %%ecx, %%esi \n\t"
"2: \n\t"
"pxor %%mm1, %%mm1 \n\t"
"movq (%%eax, %%ecx), %%mm0\n\t"
"psubw (%%esi, %%ecx), %%mm0\n\t"
#if 0
"psubw %%mm0, %%mm1 \n\t"
"pmaxsw %%mm1, %%mm0 \n\t"
#else
"pcmpgtw %%mm0, %%mm1 \n\t"
"pxor %%mm1, %%mm0 \n\t"
"psubw %%mm1, %%mm0 \n\t"
#endif
"pmaddwd %%mm6, %%mm0 \n\t"
"paddd %%mm0, %%mm7 \n\t"
"addl $8, %%ecx \n\t"
" jnz 2b \n\t"
"incl %%edx \n\t"
"cmpl %%edx, %4 \n\t"
" jnz 1b \n\t"
"movq %%mm7, %%mm0 \n\t"
"psrlq $32, %%mm7 \n\t"
"paddd %%mm7, %%mm0 \n\t"
"movd %%mm0, %0 \n\t"
:"=g" (sum)
:"r" (pic_data), "r" (ref_data), "m"(x1b), "m"(ylb)
: "%eax", "%esi", "%ecx", "%edx"
);
return sum;
--------------
and benchmarks:
on a duron:
gcc-4.3:
real 0m2.034s
user 0m1.882s
sys 0m0.017s
asm:
real 0m1.312s
user 0m1.208s
sys 0m0.016s
on a 500mhz pentium3:
gcc-4.3
real 0m4.021s
user 0m3.767s
sys 0m0.009s
asm:
real 0m2.827s
user 0m2.565s
sys 0m0.055s
--
michaelni at gmx dot at changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |michaelni at gmx dot at
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21395
