Interesting statistics on vectorization for Skylake avx512 (i9-7900) - 8.1 vs. 7.3.

[Toon Moene]

Consider the attached Fortran code (the most expensive routine, 
computation-wise, in our weather forecasting model).

verint.s.7.3 is the result of:

gfortran -g -O3 -S -march=native -mtune=native verint.f

using release 7.3.

verint.s.8.1 is the result of:

gfortran -g -O3 -S -march=native -mtune=native verint.f

using the recently released GCC 8.1.

$ wc -l verint.s.7.3 verint.s.8.1
   7818 verint.s.7.3
   6087 verint.s.8.1

$ grep vfma verint.s.7.3 | wc -l
381
$ grep vfma verint.s.8.1 | wc -l
254

but:

$ grep vfma verint.s.7.3 | grep -v ss |  wc -l
127
$ grep vfma verint.s.8.1 | grep -v ss |  wc -l
127

and:

$ grep movaps verint.s.7.3 | wc -l
306
$ grep movaps verint.s.8.3 | wc -l
270

Finally:

$ grep zmm verint.s.7.3 | wc -l
1494
$ grep zmm verint.s.8.1 | wc -l
0
$ grep ymm verint.s.7.3 | wc -l
379
$ grep ymm verint.s.8.1 | wc -l
1464

I haven't had the opportunity to test this for speed (is quite 
complicated, as I have to build several support libraries with 8.1, like 
openmpi, netcdf, hdf{4|5}, fftw ...)

-- 
Toon Moene - e-mail: toon@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands
At home: http://moene.org/~toon/; weather: http://moene.org/~hirlam/
Progress of GNU Fortran: http://gcc.gnu.org/wiki/GFortran#news
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