https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65651
--- Comment #4 from Yuri Rumyantsev <ysrumyan at gmail dot com> --- Jakub, Thanks for your comments. We will try to fix this issue ourselves. Best regards. Yuri. P.S. Note that icc does not produce such redundant cmp with zero. 2015-04-01 16:10 GMT+03:00 jakub at gcc dot gnu.org <gcc-bugzi...@gcc.gnu.org>: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65651 > > Jakub Jelinek <jakub at gcc dot gnu.org> changed: > > What |Removed |Added > ---------------------------------------------------------------------------- > CC| |jakub at gcc dot gnu.org, > | |uros at gcc dot gnu.org > > --- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- > Well, there is a significant difference between the two testcases, one uses > the > result of the comparison just in == 0 test, thus CCZmode is appropriate, the > other uses it in two comparisons, one == 0 test and one < 0 test. > For combine to match *sub<mode>_2 insn, it has to match > ix86_match_ccmode (insn, CCGOCmode) > where CCGOCmode stands for: > Add CCGOC to indicate comparisons against zero that allows > unspecified garbage in the Carry and Overflow flag. This > mode is used to simulate comparisons of (a-b) and (a+b) > against zero using sub/cmp/add operations. > But the jle instruction tests ZF || SF <> OF and thus it isn't appropriate. > So the question is if the CCGOC test isn't too restrictive, say if CCGCmode > would be sufficient (but then we'd still need to arrange for the CCGCmode to > be > used, rather than CCmode), or if the optimization you are looking for is > simply > not possible. > > -- > You are receiving this mail because: > You reported the bug.
