https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110891
--- Comment #7 from rguenther at suse dot de <rguenther at suse dot de> --- On Sat, 26 Aug 2023, pinskia at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110891 > > --- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> --- > (In reply to Andrew Pinski from comment #3) > > One thing I noticed (I don't know if causes the missed optimization) is that > > we have before PRE: > > ``` > > <bb 4> [local count: 1073531371]: > > if (a.0_1 != 0) > > goto <bb 6>; [50.00%] > > else > > goto <bb 5>; [50.00%] > > > > <bb 5> [local count: 536765686]: > > if (_28 == &d) > > goto <bb 9>; [30.00%] > > else > > goto <bb 7>; [70.00%] > > > > <bb 6> [local count: 536765685]: > > if (_28 == &d) > > goto <bb 9>; [30.00%] > > else > > goto <bb 7>; [70.00%] > > ``` > > Which obvious should just be `if (_28 == &d) goto bb9; else goto bb7;` and > > not check `a.0_1` at all. > > I wonder if ifcombine could optimize that instead of requiring PRE. I think > that might even fix the issue too. Note it's the tail-merging code that optimizes this, not PRE (yeah, those passes should be ripped apart)
