On Wed, Sep 21, 2016 at 9:13 AM, Andrew Pinski <pins...@gmail.com> wrote: > Hi, > While looking through bug reports, I noticed someone had reported > that LTO caused the vectorizer not to kick in. Originally it was not > obvious why it would change the behavior since this was a simple > program with nothing out of the ordinary. Well it turned out paths > leading to the exit(0); at the end of main was being marked as cold > and in the LTO case the funciton (which had loop which should have > been vectorized) was considered local and being marked as cold as it > was only called now from the path leading to the exit(0); Since > exit(0); is considered a normal exit path, there is no reason to mark > it as being as a cold path; let the other predicate handle it. > > So this patch changes the predicate for exit(0) not to mark the paths > leading up to that function call as being cold. Note this patch only > disables that when the argument is a literal zero so if we a PHI node > which contains the exit value, we still cause those paths to be > considered cold; this will be for another patch.
Hmm, it also doesn't work for main calling a function not returning but exiting with exit (0) (it will be discovered as noreturn). I don't think that treating exit (0) as generally not terminating a cold code sequence is good either. Predictions are always hard I guess ... But the thing to improve is maybe the different handling of main with respect to the guessed profile -- this is something that should not happen inconsistently between LTO / non-LTO as main is special in all cases. Honza? Richard. > OK? Bootstrapped and tested on aarch64-linux-gnu with no regressions. > Also tested it with SPEC CPU 2006 with no performance regressions. > > Thanks, > Andrew Pinski > > ChangeLog: > * predict.c (is_exit_with_zero_arg): New function. > (tree_bb_level_predictions): Don't consider paths leading to exit(0) > as nottaken.
