https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78379
--- Comment #8 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
(In reply to Thomas Koenig from comment #6)
> > You may notice I was invoking the wrong executable in what I posted in
> > comment #3. I did rerun the correct one several times and tried it with
> > -mavx -mprefer-avx128. I get the same poor results regardless.
>
> Several things could go wrong here...
>
> If you run the benchmark under gdb and break, then type
> "disassemble $pc,$pc+200", do you actually end up in the right
> program part (the one with AVX instructions)?
452 f32 += t1[l - ll + 1 + ((i - ii + 3) <<
8) - 257]
(gdb) disassemble $pc,$pc+200
Dump of assembler code from 0x7ffff7af3554 to 0x7ffff7af361c:
=> 0x00007ffff7af3554 <aux_matmul_r8+5220>: vaddpd %ymm12,%ymm4,%ymm4
0x00007ffff7af3559 <aux_matmul_r8+5225>: vmulpd %ymm10,%ymm15,%ymm12
0x00007ffff7af355e <aux_matmul_r8+5230>: vaddpd %ymm11,%ymm5,%ymm5
0x00007ffff7af3563 <aux_matmul_r8+5235>: vmulpd %ymm14,%ymm15,%ymm15
0x00007ffff7af3568 <aux_matmul_r8+5240>: vmulpd %ymm10,%ymm13,%ymm10
0x00007ffff7af356d <aux_matmul_r8+5245>: vaddpd %ymm12,%ymm6,%ymm6
0x00007ffff7af3572 <aux_matmul_r8+5250>: vmulpd %ymm14,%ymm13,%ymm14
0x00007ffff7af3577 <aux_matmul_r8+5255>: vaddpd %ymm15,%ymm8,%ymm8
0x00007ffff7af357c <aux_matmul_r8+5260>: vaddpd %ymm10,%ymm7,%ymm7
0x00007ffff7af3581 <aux_matmul_r8+5265>: vaddpd %ymm14,%ymm9,%ymm9
0x00007ffff7af3586 <aux_matmul_r8+5270>: ja 0x7ffff7af3433
<aux_matmul_r8+4931>
0x00007ffff7af358c <aux_matmul_r8+5276>: mov -0x801f8(%rbp),%rdx
0x00007ffff7af3593 <aux_matmul_r8+5283>: vhaddpd %ymm9,%ymm9,%ymm13
0x00007ffff7af3598 <aux_matmul_r8+5288>: vhaddpd %ymm8,%ymm8,%ymm15
0x00007ffff7af359d <aux_matmul_r8+5293>: vhaddpd %ymm7,%ymm7,%ymm7
0x00007ffff7af35a1 <aux_matmul_r8+5297>: vperm2f128
$0x1,%ymm13,%ymm13,%ymm11
0x00007ffff7af35a7 <aux_matmul_r8+5303>: vhaddpd %ymm5,%ymm5,%ymm5
0x00007ffff7af35ab <aux_matmul_r8+5307>: vperm2f128
$0x1,%ymm15,%ymm15,%ymm8
0x00007ffff7af35b1 <aux_matmul_r8+5313>: vaddpd %ymm11,%ymm13,%ymm12
0x00007ffff7af35b6 <aux_matmul_r8+5318>: vperm2f128
$0x1,%ymm7,%ymm7,%ymm13
0x00007ffff7af35bc <aux_matmul_r8+5324>: vaddpd %ymm8,%ymm15,%ymm14
0x00007ffff7af35c1 <aux_matmul_r8+5329>: vhaddpd %ymm6,%ymm6,%ymm6
---Type <return> to continue, or q <return> to quit---
0x00007ffff7af35c5 <aux_matmul_r8+5333>: vaddsd
-0x80068(%rbp),%xmm12,%xmm10
0x00007ffff7af35cd <aux_matmul_r8+5341>: vaddsd
-0x80070(%rbp),%xmm14,%xmm9
0x00007ffff7af35d5 <aux_matmul_r8+5349>: vperm2f128
$0x1,%ymm5,%ymm5,%ymm14
0x00007ffff7af35db <aux_matmul_r8+5355>: vhaddpd %ymm4,%ymm4,%ymm4
0x00007ffff7af35df <aux_matmul_r8+5359>: vaddpd %ymm13,%ymm7,%ymm11
0x00007ffff7af35e4 <aux_matmul_r8+5364>: vmovsd %xmm10,-0x80068(%rbp)
0x00007ffff7af35ec <aux_matmul_r8+5372>: vperm2f128
$0x1,%ymm6,%ymm6,%ymm10
0x00007ffff7af35f2 <aux_matmul_r8+5378>: vperm2f128
$0x1,%ymm4,%ymm4,%ymm13
0x00007ffff7af35f8 <aux_matmul_r8+5384>: vmovsd %xmm9,-0x80070(%rbp)
0x00007ffff7af3600 <aux_matmul_r8+5392>: vaddpd %ymm14,%ymm5,%ymm9
0x00007ffff7af3605 <aux_matmul_r8+5397>: vhaddpd %ymm0,%ymm0,%ymm0
0x00007ffff7af3609 <aux_matmul_r8+5401>: vaddsd
-0x80058(%rbp),%xmm11,%xmm12
0x00007ffff7af3611 <aux_matmul_r8+5409>: vaddpd %ymm10,%ymm6,%ymm15
0x00007ffff7af3616 <aux_matmul_r8+5414>: vaddpd %ymm13,%ymm4,%ymm11
0x00007ffff7af361b <aux_matmul_r8+5419>: vperm2f128
$0x1,%ymm0,%ymm0,%ymm13
End of assembler dump.
>
> Or does your machine prefer AVX128?
>
> To find out, what are the timings for inline code using
>
> -mavx -Ofast
>
> -mavx -mprefer=avx128 -Ofast
>
> ?
$ gfc -finline-matmul-limit=64 -Ofast compare.f90
$ ./a.out
=========================================================
================ MEASURED GIGAFLOPS =
=========================================================
Matmul Matmul
fixed Matmul variable
Size Loops explicit refMatmul assumed explicit
=========================================================
2 2000 4.933 0.045 0.086 0.144
4 2000 1.418 0.225 0.271 0.347
8 2000 2.168 0.616 1.296 1.830
16 2000 5.330 2.824 1.784 2.907
32 2000 6.239 3.488 1.446 3.406
64 2000 2.650 2.746 1.552 2.691
$ gfc -finline-matmul-limit=64 -mavx -Ofast compare.f90
$ ./a.out
=========================================================
================ MEASURED GIGAFLOPS =
=========================================================
Matmul Matmul
fixed Matmul variable
Size Loops explicit refMatmul assumed explicit
=========================================================
2 2000 6.934 0.042 0.091 0.134
4 2000 1.320 0.181 0.365 0.252
8 2000 1.007 0.446 1.595 0.982
16 2000 0.581 1.163 2.411 1.180
32 2000 1.346 1.276 2.061 1.277
64 2000 1.397 1.327 2.288 1.328
$ gfc -finline-matmul-limit=64 -mavx -mprefer-avx128 -Ofast compare.f90
$ ./a.out
=========================================================
================ MEASURED GIGAFLOPS =
=========================================================
Matmul Matmul
fixed Matmul variable
Size Loops explicit refMatmul assumed explicit
=========================================================
2 2000 5.021 0.045 0.088 0.139
4 2000 1.607 0.202 0.288 0.341
8 2000 2.482 0.575 0.743 1.861
16 2000 5.674 2.804 1.809 2.792
32 2000 6.323 3.460 1.478 3.293
64 2000 2.714 2.832 1.582 2.694
If I put -mavx -prefer-avx128 in the Makefile.am I get as good or better than
without your patch. I also see none of the HAVE_AVX defined in config.
$ gfc -finline-matmul-limit=0 -Ofast compare.f90
$ ./a.out
=========================================================
================ MEASURED GIGAFLOPS =
=========================================================
Matmul Matmul
fixed Matmul variable
Size Loops explicit refMatmul assumed explicit
=========================================================
2 2000 0.043 0.041 0.034 0.043
4 2000 0.272 0.234 0.223 0.256
8 2000 0.835 1.687 1.627 1.709
16 2000 2.886 2.887 2.859 2.869
32 2000 4.733 3.494 4.755 4.652
64 2000 6.933 2.837 6.933 6.877
128 2000 7.949 3.285 8.705 7.914
256 477 10.040 3.447 9.999 9.951
512 59 8.885 2.341 8.923 8.940
1024 7 8.937 1.367 8.978 8.991
2048 1 8.799 1.672 8.831 8.854
The following in config.h.in for what it is worth:
/* Define if AVX instructions can be compiled. */
#undef HAVE_AVX
/* Define if AVX2 instructions can be compiled. */
#undef HAVE_AVX2
/* Define if AVX512f instructions can be compiled. */
#undef HAVE_AVX512F
