https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64434
--- Comment #10 from rguenther at suse dot de <rguenther at suse dot de> --- On December 29, 2014 5:56:25 PM CET, ysrumyan at gmail dot com <gcc-bugzi...@gcc.gnu.org> wrote: >https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64434 > >--- Comment #8 from Yuri Rumyantsev <ysrumyan at gmail dot com> --- >The issue is caused by operand canonicalization, i.e. there is special >operand odering for commutative operations to have the same >representation for a + b and b + a. If computation of second operand >requires more operations this may lead to live range increasing ( for >live variables computed by first operand). If we swap these operands >we get live range shrinking which is essential for 32-bit targets >having only few registers. > >Hope it will help you to understand the problem. This is essentially a scheduling issue (and thus also related to TER). I played with the idea of a SSA life-range reducing BB scheduling without much success. The trick of swapping operands to expand the expensive one first sounds good to me. >2014-12-29 19:36 GMT+03:00 hjl.tools at gmail dot com ><gcc-bugzi...@gcc.gnu.org>: >> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64434 >> >> --- Comment #7 from H.J. Lu <hjl.tools at gmail dot com> --- >> r216728 generates much longer code sequences. Where does it come >from? >> Does -m64 also generate longer code sequences? >> >> -- >> You are receiving this mail because: >> You reported the bug.
