https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69671
--- Comment #17 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to ktkachov from comment #16) > (In reply to Jakub Jelinek from comment #15) > > Yeah, my preference is to back out the cse.c one-liner for GCC 6. > > IMO the cse.c patch is the correct fix for the code quality regression seen > on the gcc.target/arm/wmul-1.c and gcc.target/arm/wmul-2.c tests on arm when > tuning for -mcpu=cortex-a9, which is a fairly popular arm target. While it may be a correct fix, IMHO it is not appropriate for this late in the release cycle. > The patch didn't have a performance impact on SPEC2000 and SPEC2006 on arm, > but I did see the adverse code quality effect from gcc.target/arm/wmul-1.c > and gcc.target/arm/wmul-2.c on a popular embedded benchmark without it. > > So reverting this would cause performance regressions on some normal integer > code on arm (not using intrinsics). > > How risky at this stage is it to do the define_subst fix for the AVX > patterns? It affects lots of patterns in the i?86 backend, just grep for 0C constraints, especially the subst.md use adds it to most of the vector instructions even when they don't have it explicitly. So, it is very risky to change those now.
