https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81616
--- Comment #32 from Andrew Roberts <andrewm.roberts at sky dot com> ---
For what its worth, here's what the latest and greatest from the competition
has to offer:
/usr/local/llvm-5.0.1-rc2/bin/clang -march=znver1 -mtune=znver1 -O3 matrix.c -o
matrix
mult took 887141 clocks
/usr/local/llvm-5.0.1-rc2/biznver1 -O3 mt19937ar.c -o mt19937ar
mt19937ar took 402282 clocks
/usr/local/llvm-5.0.1-rc2/bin/clang -march=znver1 -mtune=znver1 -Ofast matrix.c
-o matrix
mult took 760913 clocks
/usr/local/llvm-5.0.1-rc2/bin/clang -march=znver1 -mtune=znver1 -Ofast
mt19937ar.c -o mt19937ar
mt19937ar took 392527 clocks
current gcc-8 snapshot:
/usr/local/gcc/bin/gcc -march=znver1 -mtune=znver1 -Ofast matrix.c -o matrix
mult took 364775 clocks
/usr/local/gcc/bin/gcc -march=znver1 -mtune=znver1 -Ofast -o mt19937ar
mt19937ar.c
mt19937ar took 430804 clocks
current gcc-8 snapshot + extra opts to improve znver1 performance
/usr/local/gcc/bin/gcc -march=znver1 -mtune=znver1 -mprefer-vector-width=none
-mno-fma -Ofast matrix.c -o matrix
mult took 130329 clocks
/usr/local/gcc/bin/gcc -march=znver1 -mtune=znver1 -mno-avx2 -Ofast -o
mt19937ar mt19937ar.c
mt19937ar took 387728 clocks
So gcc loses on mt19937ar.c without -mno-avx2
But gcc wins big on matrix.c, especially with -mprefer-vector-width=none
-mno-fma
