https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112844
--- Comment #2 from Petr Skocik <pskocik at gmail dot com> --- (In reply to Jakub Jelinek from comment #1) > With -Os you ask the code to be small. So, while internally the hint is > still present in edge probabilities, -Os is considered more important and > certain code changes based on the probabilities aren't done if they are > known or expected to result in larger code. Thanks. I very much like the codegen I get with gcc -Os, often better than what I get with clang. But the sometimes counter-obvious branch layout at -Os is annoying to me, especially considering I've measured it a couple of times as being the source of a slowdown. Sure you can save a (most-often-than not 2-byte) jump by conditionally jumping over an unlikely branch instead of conditionally jumping to an unlikely branch placed after ret and having it jump back in the function body (the latter is what all the other compilers do at -Os), but I'd rather have the code spend the extra two bytes and have my happy paths be fall-through as they should be.
