> > I have benchmarked this quite thoroughly while switching the defaults for Core > and Zen. Disabling alignment is pretty much consistent for specfp/int for > 2000,2006 and 2017 (last is Zen only) and quite consistent one. I will > analyze > fma3d. It did not show with the alignment change alone, so it may be related > to other costs or just bad luck.
I have opened https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83232 for that. The problem is that SLP gives up vectorization when it sees vectorized used in the same basic block. Preivously there was alignment prologue while now we fully unroll the loop. Missed SLP introduce memory mismatch stall. I am bit lost on why SLP gives up though. Honza
