https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79390
--- Comment #27 from rguenther at suse dot de <rguenther at suse dot de> --- On Wed, 12 Apr 2017, jakub at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79390 > > --- Comment #26 from Jakub Jelinek <jakub at gcc dot gnu.org> --- > Created attachment 41189 > --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41189&action=edit > gcc7-pr79390-ecm.patch > > Untested fix for the -O3 -ffast-math -march=haswell case. > The difference between -fno-fast-math and -ffast-math is in: > if (swap_commutative_operands_p (op2, op3) > && ((reversed = reversed_comparison_code_parts (code, op0, op1, NULL)) > != UNKNOWN)) > { > std::swap (op2, op3); > code = reversed; > } > > swap_commutative_operands_p is true in both cases, but without > -ffast-math reversed_comparison_code_parts fails (returns UNKNOWN), so we > don't > try that order and succeed, while with -ffast-math it doesn't fail, returns > LE, > but we reject it in the predicates of the cmov insn and thus don't emit > anything. This patch just retries with the other order of operands in that > case. Looks sensible.
