http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50176
--- Comment #12 from rguenther at suse dot de <rguenther at suse dot de> 2012-01-11 08:56:27 UTC --- On Tue, 10 Jan 2012, ebotcazou at gcc dot gnu.org wrote: > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50176 > > Eric Botcazou <ebotcazou at gcc dot gnu.org> changed: > > What |Removed |Added > ---------------------------------------------------------------------------- > CC| |ebotcazou at gcc dot > | |gnu.org > > --- Comment #11 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-01-10 > 22:03:43 UTC --- > > thus there is a store between the load and the zero_extend (and combine > > only combines forward, not backward): > > > > /* Verify that I2 and I1 are valid for combining. */ > > if (! can_combine_p (i2, i3, i0, i1, NULL_RTX, NULL_RTX, &i2dest, &i2src) > > > > already fails. > > combine is a peephole optimizer so you cannot ask it to combine insns with 8 > other intervening insns between them. It looks like we have a real problem > with extensions though and the good approach (backward combining) appears to > be > that of the REE pass, but it's too limited for the time being. Yeah, it's a bit unfortunate that combines behavior depends on the insn scheduling ...
