https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84114
--- Comment #6 from Steve Ellcey <sje at gcc dot gnu.org> --- (In reply to Wilco from comment #5) > (In reply to Steve Ellcey from comment #4) > > While teaching the reassociation pass about fma's seems like the right > > answer would it be reasonable (and simpler) to do the fma pass > > (pass_optimize_widening_mul) before > > the reassociation pass (pass_reassoc) to get the most fma's? > > > > That fixes my small test case but I haven't done a bigger performance check > > to see what the overall impact would be. > > I don't know what else that would affect since the reassociation phase runs > very early - and it's late at this stage. My patch seems much safer. Even > easier might be to return 1 for FLOAT_MODE PLUS_EXPR in > aarch64_reassociation_width. Then we can fix the reassociation phase in GCC9. Moving the fma phase did not have a good performance impact (it was worse). Your patch of setting the reassociation width to 1 did help performance on ThunderX2.
