------- Comment #27 from ubizjak at gmail dot com 2008-01-22 12:20 -------
As already noted by Richi in Comment #9, the difference is in usage of %rax.
gcc-4.2 generates:
...
addq $7, %rax
leaq (%rax,%rbp,2), %r10
leaq (%rax,%rdx,2), %rdx
leaq (%rax,%rdi,2), %rdi
movq (%rcx), %rsi
movq (%r13), %rcx
leaq (%rax,%r9,2), %r9
leaq (%rax,%r8,2), %r8
leaq (%rax,%r14,2), %r11
addq $8, %rbp
movsd (%rdx), %xmm3
leaq (%rax,%rsi,2), %rsi
leaq (%rax,%rcx,2), %rcx
...
movsd %xmm7, (%rcx)
subsd %xmm1, %xmm10
addsd %xmm1, %xmm0
movsd %xmm8, (%rsi)
movsd %xmm0, (%rdi)
movapd %xmm12, %xmm0
subsd %xmm3, %xmm12
addsd %xmm3, %xmm0
movsd %xmm0, (%r8)
movsd %xmm10, (%r9)
movsd %xmm12, (%rdx)
jg .L26
where gcc-4.3 limps along with:
...
leaq 7(%rax), %r9
movq %rbx, -64(%rsp)
movq -56(%rsp), %rcx
addq %r10, %r10
movsd 7(%rax,%rdx), %xmm3
movsd (%r9,%rbx,2), %xmm8
movq (%r11), %rbx
movsd 7(%rax,%r10), %xmm5
addq %r8, %r8
addq %rdi, %rdi
movsd 7(%rax,%r8), %xmm12
movsd 15(%rbx), %xmm2
leaq (%r9,%rbp,2), %r9
movsd 7(%rbx), %xmm1
...
movsd %xmm0, 7(%rax,%r9,2)
movapd %xmm10, %xmm0
movsd %xmm7, 7(%rax,%rcx)
subsd %xmm1, %xmm10
addsd %xmm1, %xmm0
movsd %xmm8, 7(%rax,%rsi)
movsd %xmm0, 7(%rax,%rdi)
movapd %xmm12, %xmm0
subsd %xmm3, %xmm12
addsd %xmm3, %xmm0
movsd %xmm0, 7(%rax,%r8)
movsd %xmm10, 7(%rax,%r10)
movsd %xmm12, 7(%rax,%rdx)
jg .L17
The difference is in offseted addresses. Looking at the tree dumps, it is
obvious that the problem is in fre pass.
At the end of the loop (line 685+ in _.034.fre) gcc-4.2 transforms every
seqence of:
D.2013_432 = ___fp_256 + 40B;
D.2014_433 = *D.2013_432;
D.2068_434 = (long int *) D.2014_433;
D.2069_435 = D.2068_434 + 7B;
D.2070_436 = (long int) D.2069_435;
D.2094_437 = ___r3_35 << 1;
D.2095_438 = D.2070_436 + D.2094_437;
D.2096_439 = (double *) D.2095_438;
*D.2096_439 = ___F64V53_431;
D.2013_440 = ___fp_256 + 40B;
D.2014_441 = *D.2013_440;
D.2068_442 = (long int *) D.2014_441;
D.2069_443 = D.2068_442 + 7B;
D.2070_444 = (long int) D.2069_443;
D.2091_445 = ___r4_257 << 1;
D.2092_446 = D.2070_444 + D.2091_445;
D.2093_447 = (double *) D.2092_446;
*D.2093_447 = ___F64V52_430;
D.2013_448 = ___fp_256 + 40B;
D.2014_449 = *D.2013_448;
D.2068_450 = (long int *) D.2014_449;
D.2069_451 = D.2068_450 + 7B;
D.2070_452 = (long int) D.2069_451;
...
into:
D.2013_432 = D.2013_286;
D.2014_433 = D.2014_287;
D.2068_434 = D.2068_288;
D.2069_435 = D.2069_289;
D.2070_436 = D.2070_290;
D.2094_437 = D.2094_366;
D.2095_438 = D.2095_367;
D.2096_439 = D.2096_368;
*D.2096_439 = ___F64V53_431;
D.2013_440 = D.2013_286;
D.2014_441 = D.2014_287;
D.2068_442 = D.2068_288;
D.2069_443 = D.2069_289;
D.2070_444 = D.2070_290;
D.2091_445 = D.2091_357;
D.2092_446 = D.2092_358;
D.2093_447 = D.2093_359;
*D.2093_447 = ___F64V52_430;
D.2013_448 = D.2013_286;
D.2014_449 = D.2014_287;
D.2068_450 = D.2068_288;
D.2069_451 = D.2069_289;
D.2070_452 = D.2070_290;
D.1994_453 = D.1994_258;
D.2040_454 = D.2040_347;
D.2041_455 = D.2041_348;
D.2089_456 = D.2089_349;
D.2090_457 = D.2090_350;
...
and this is optimized in further passes into:
*D.2096 = ___F64V32 + ___F64V45;
*D.2093 = ___F64V31 + ___F64V42;
*D.2090 = ___F64V32 - ___F64V45;
*D.2088 = ___F64V31 - ___F64V42;
*D.2084 = ___F64V28 + ___F64V39;
*D.2081 = ___F64V27 + ___F64V36;
*D.2077 = ___F64V28 - ___F64V39;
*D.2074 = ___F64V27 - ___F64V36;
However, for some reason gcc-4.3 transforms only _some_ instructions (line 708+
in _.085t.fre dump), creating:
D.1683_428 = D.1683_282;
D.1684_429 = D.1684_283;
D.1738_430 = D.1738_284;
D.1739_431 = D.1739_285;
D.1740_432 = D.1740_286;
D.1764_433 = D.1764_362;
D.1765_434 = D.1765_363;
D.1766_435 = D.1766_364;
*D.1766_435 = ___F64V53_427;
D.1683_436 = D.1683_282;
D.1684_437 = *D.1683_436;
D.1738_438 = (long unsigned int) D.1684_437;
D.1739_439 = D.1738_438 + 7;
D.1740_440 = (long int) D.1739_439;
D.1761_441 = D.1761_353;
D.1762_442 = D.1740_440 + D.1761_441;
D.1763_443 = (double *) D.1762_442;
*D.1763_443 = ___F64V52_426;
D.1683_444 = D.1683_282;
D.1684_445 = *D.1683_444;
D.1738_446 = (long unsigned int) D.1684_445;
D.1739_447 = D.1738_446 + 7;
D.1740_448 = (long int) D.1739_447;
...
which leaves us with:
*D.1766 = ___F64V32 + ___F64V45;
*(double *) (D.1761 + (long int) ((long unsigned int) *pretmp.33 + 7)) =
___F64V31 + ___F64V42;
*(double *) ((long int) ((long unsigned int) *pretmp.33 + 7) + (*temp.65 <<
1)) = ___F64V32 - ___F64V45;
*(double *) ((long int) ((long unsigned int) *pretmp.33 + 7) + (*D.1685 <<
1)) = ___F64V31 - ___F64V42;
*(double *) ((long int) ((long unsigned int) *pretmp.33 + 7) + (*temp.61 <<
1)) = ___F64V28 + ___F64V39;
*(double *) ((long int) ((long unsigned int) *pretmp.33 + 7) + (*pretmp.152
<< 1)) = ___F64V27 + ___F64V36;
*(double *) ((long int) ((long unsigned int) *pretmp.33 + 7) + (*pretmp.147
<< 1)) = ___F64V28 - ___F64V39;
*(double *) ((long int) ((long unsigned int) *pretmp.33 + 7) + (*___fp.47 <<
1)) = ___F64V27 - ___F64V36;
and creates unoptimal asm as above.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33928
