https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81616

--- Comment #28 from Andrew Roberts <andrewm.roberts at sky dot com> ---
Adding -mno-avx2 into the mix was a marginal win, but only just showing out of
the noise:

/usr/local/gcc/bin/gcc -march=znver1 -mtune=znver1 -mprefer-vector-width=none
-mno-fma -mno-avx2 -O3 matrix.c -o matrix
       mult took     121397 clocks
       mult took     124373 clocks
       mult took     125345 clocks

/usr/local/gcc/bin/gcc -march=znver1 -mtune=znver1 -mprefer-vector-width=none
-mno-fma -O3 matrix.c -o matrix
        mult took     123262 clocks
        mult took     128193 clocks
        mult took     125891 clocks

Using -Ofast instead of -O3

/usr/local/gcc/bin/gcc -march=znver1 -mtune=znver1 -mprefer-vector-width=none
-mno-fma -Ofast matrix.c -o matrix
        mult took     125163 clocks
        mult took     123799 clocks
        mult took     122808 clocks

/usr/local/gcc/bin/gcc -march=znver1 -mtune=znver1 -mprefer-vector-width=none
-mno-fma -mno-avx2 -Ofast matrix.c -o matrix
        mult took     130189 clocks
        mult took     122726 clocks
        mult took     123686 clocks

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