[kllrnohj]

> with the possibly buggy -O3

-O3 isn't buggy on either GCC or Clang. Are you thinking of -Ofast and/or -ffast-math that disregard standards compliance? Those aren't part of -O3.

[BoingBoomTschak]

-O3 itself isn't "buggy", but since it uses more optimizations, it can reveal issues in them. Other Gentoo users know: e.g. https://bugs.gentoo.org/show_bug.cgi?id=941208 https://bugs.gentoo.org/show_bug.cgi?id=940923 (search O3 in the bugzilla).

[kllrnohj]

strict-aliasing, which is what caused that bug to manifest, is enabled at O2.

[BoingBoomTschak]

Yep, it's what caused the bug to manifest, but who knows if that UB would have caused -O2 optimizations to mangle the result as well.

EDIT: first one is -funswitch-loops, though

[kllrnohj]

Probably would have. There's no shortage of UB bugs revealed by O2 after all, including major security issues.