SSE/AVX matrix multiply
@rygorous
https://gist.github.com/rygorous/4172889


### GCC 7
[nwolovick@eulogia SIMD]$ for i in {0..3}; do echo "-O$i"; gcc -O$i -march=knl gistfile1.cpp; ./a.out ; done
-O0
all ok.
         ref: 1079.34 cycles
         SSE: 448.48 cycles
    AVX_4mem: 464.23 cycles
       AVX_8: 317.98 cycles
-O1
all ok.
         ref: 154.28 cycles
         SSE: 45.19 cycles
    AVX_4mem: 83.21 cycles
       AVX_8: 71.94 cycles
-O2
all ok.
         ref: 132.61 cycles
         SSE: 36.71 cycles
    AVX_4mem: 71.07 cycles
       AVX_8: 64.14 cycles
-O3
all ok.
         ref: 11.28 cycles
         SSE: 38.62 cycles
    AVX_4mem: 72.81 cycles
       AVX_8: 62.41 cycles

### GCC 5.4
nicolasw@zx81:~/SIMD$ for i in {0..3}; do echo "-O$i"; gcc -O$i -march=haswell gistfile1.cpp; ./a.out ; done
-O0
all ok.
         ref: 239.35 cycles
         SSE: 151.48 cycles
    AVX_4mem: 153.38 cycles
       AVX_8: 105.78 cycles
-O1
all ok.
         ref: 60.46 cycles
         SSE: 19.60 cycles
    AVX_4mem: 18.24 cycles
       AVX_8: 11.47 cycles
-O2
all ok.
         ref: 53.20 cycles
         SSE: 16.61 cycles
    AVX_4mem: 15.81 cycles
       AVX_8: 10.23 cycles
-O3
all ok.
         ref: 44.26 cycles
         SSE: 14.60 cycles
    AVX_4mem: 15.77 cycles
       AVX_8: 9.73 cycles

### GCC 7
nicolasw@zx81:~/SIMD$ for i in {0..3}; do echo "-O$i"; gcc-7 -O$i -march=haswell gistfile1.cpp; ./a.out ; done
-O0
all ok.
         ref: 240.48 cycles
         SSE: 150.43 cycles
    AVX_4mem: 153.92 cycles
       AVX_8: 110.06 cycles
-O1
all ok.
         ref: 61.81 cycles
         SSE: 19.60 cycles
    AVX_4mem: 18.24 cycles
       AVX_8: 12.30 cycles
-O2
all ok.
         ref: 51.76 cycles
         SSE: 16.86 cycles
    AVX_4mem: 15.77 cycles
       AVX_8: 11.28 cycles
-O3
all ok.
         ref: 10.45 cycles
         SSE: 14.87 cycles
    AVX_4mem: 15.57 cycles
       AVX_8: 9.33 cycles

### GCC 5.4
nwolovick@mendieta23 SIMD]$ ./0; ./1; ./2; ./3
all ok.
         ref: 293.09 cycles
         SSE: 175.70 cycles
    AVX_4mem: 179.26 cycles
       AVX_8: 165.44 cycles
all ok.
         ref: 73.46 cycles
         SSE: 25.81 cycles
    AVX_4mem: 22.12 cycles
       AVX_8: 17.25 cycles
all ok.
         ref: 72.72 cycles
         SSE: 24.57 cycles
    AVX_4mem: 23.18 cycles
       AVX_8: 16.67 cycles
all ok.
         ref: 68.44 cycles
         SSE: 24.35 cycles
    AVX_4mem: 20.28 cycles
       AVX_8: 17.29 cycles