[Bug libfortran/78379] Processor-specific versions for matmul

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78379

--- Comment #36 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
Results look very good.

Gfortran 7, no patch gives:

$ gfc7 -static -Ofast -ftree-vectorize compare.f90 
$ ./a.out 
 =========================================================
 ================            MEASURED GIGAFLOPS          =
 =========================================================
                 Matmul                           Matmul
                 fixed                 Matmul     variable
 Size  Loops     explicit   refMatmul  assumed    explicit
 =========================================================
    2  2000      4.706      0.046      0.094      0.162
    4  2000      1.246      0.246      0.305      0.351
    8  2000      1.410      0.605      0.958      1.791
   16  2000      5.413      2.787      2.228      2.615
   32  2000      4.676      3.416      4.622      4.618
   64  2000      6.368      2.652      6.339      6.167
  128  2000      8.165      2.998      8.118      8.260
  256   477      9.334      3.202      9.248      9.355
  512    59      8.730      2.239      8.596      8.730
 1024     7      8.805      1.378      8.673      8.812
 2048     1      8.781      1.728      8.649      8.789

Latest gfortran trunk with patch gives:

$ gfc -static -Ofast -ftree-vectorize compare.f90 
$ ./a.out 
 =========================================================
 ================            MEASURED GIGAFLOPS          =
 =========================================================
                 Matmul                           Matmul
                 fixed                 Matmul     variable
 Size  Loops     explicit   refMatmul  assumed    explicit
 =========================================================
    2  2000      4.738      0.048      0.092      0.172
    4  2000      1.438      0.248      0.305      0.378
    8  2000      1.511      0.617      1.177      1.955
   16  2000      5.426      2.810      1.854      2.881
   32  2000      4.688      3.314      4.357      5.091
   64  2000      6.669      2.674      6.629      7.110
  128  2000      9.139      3.000      9.076      9.131
  256   477     10.495      3.184     10.466     10.516
  512    59      9.577      2.189      9.477      9.635
 1024     7      9.593      1.381      9.519      9.658
 2048     1      9.722      1.709      9.625      9.785