https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114761
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|tree-optimization |middle-end
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I am not so sure which one is better really.
So what I think clang is doing is this, turn if the statements into a switch
and then expanding the switch into a bunch of if statements and have the
highest probability one first. This is a decent way to "rotate" the if
statements. But I don't think it will help this case though because GCC still
likes to combine them into one without a branch (which might be better
overall).
I noticed that clang does not do any combining and producing ccmp for aarch64
(even if you remove all of the [[unlikely]]/[[likely]]). So it produces worse
code there. a branch for the combined unlikely case might be worse.
Also gcc tends to ignore the probilitity when it comes to combining because
combining almost improves code ...
