[Bug rtl-optimization/21395] Performance degradation when building code that uses MMX intrinsics with gcc-4.0.0

[michaelni at gmx dot at]

------- 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