https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81616
--- Comment #46 from Andrew Roberts <andrewm.roberts at sky dot com> --- With the latest snapshot: gcc version 8.0.1 20180121 For the mt19937ar things now look reasonable without any strange options on Ryzen. Top 5 mt19937ar took 226849 clocks -march=amdfam10 -mtune=btver2 mt19937ar took 228970 clocks -march=amdfam10 -mtune=barcelona mt19937ar took 229494 clocks -march=bdver1 -mtune=btver1 mt19937ar took 229524 clocks -march=nano -mtune=nano mt19937ar took 230003 clocks -march=opteron-sse3 -mtune=athlon64-sse3 mt19937ar took 233793 clocks -march=k8-sse3 -mtune=x86-64 mt19937ar took 241700 clocks -march=corei7 -mtune=generic mt19937ar took 242373 clocks -march=nano-3000 -mtune=znver1 mt19937ar took 245550 clocks -march=k8-sse3 -mtune=haswell mt19937ar took 251431 clocks -march=znver1 -mtune=generic mt19937ar took 262200 clocks -march=znver1 -mtune=znver1 mt19937ar took 276993 clocks -march=haswell -mtune=haswell Bot 5 mt19937ar took 341326 clocks -march=nano-x4 -mtune=silvermont mt19937ar took 341750 clocks -march=core-avx-i -mtune=nocona mt19937ar took 342457 clocks -march=k8 -mtune=znver1 mt19937ar took 347453 clocks -march=ivybridge -mtune=bonnell mt19937ar took 364041 clocks -march=haswell -mtune=core-avx-i with -mno-avx2 mt19937ar took 235997 clocks -march=znver1 -mtune=opteron mt19937ar took 233921 clocks -march=nano-1000 -mtune=x86-64 mt19937ar took 243452 clocks -march=znver1 -mtune=x86-64 mt19937ar took 243540 clocks -march=silvermont -mtune=generic mt19937ar took 247113 clocks -march=znver1 -mtune=generic mt19937ar took 241368 clocks -march=nano-2000 -mtune=haswell mt19937ar took 247806 clocks -march=znver1 -mtune=znver1 Compare this with it taking 430875 clocks originally for -march=znver1 -mtune=znver1 On Haswell Top 5 mt19937ar took 220000 clocks -march=amdfam10 -mtune=amdfam10 mt19937ar took 220000 clocks -march=amdfam10 -mtune=athlon64 mt19937ar took 220000 clocks -march=amdfam10 -mtune=athlon64-sse3 mt19937ar took 220000 clocks -march=amdfam10 -mtune=athlon-fx mt19937ar took 220000 clocks -march=amdfam10 -mtune=barcelona mt19937ar took 220000 clocks -march=corei7-avx -mtune=x86-64 mt19937ar took 230000 clocks -march=haswell -mtune=haswell mt19937ar took 240000 clocks -march=haswell -mtune=generic mt19937ar took 260000 clocks -march=haswell -mtune=x86-64 Bot 5 (all various shades of mtune=bdverZ or mtune=btverZ) mt19937ar took 310000 clocks -march=core-avx2 -mtune=bdver1 mt19937ar took 310000 clocks -march=haswell -mtune=bdver1 mt19937ar took 310000 clocks -march=skylake -mtune=bdver1
