As seen here https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=992.70.0 there was a 4.5% exec time slowdown of the 433.milc SPEC 2006 benchmark between commits r15-2045-g61c21a719e205f r15-2061-gacd4ab8d6e8938 when run with -Ofast -march=native -flto on an AMD Zen4 machine.
Might be: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=1e3aa9c9278db69d4bdb661a750a7268789188d6
(In reply to Andrew Pinski from comment #1) > Might be: > https://gcc.gnu.org/git/?p=gcc.git;a=commit; > h=1e3aa9c9278db69d4bdb661a750a7268789188d6 I've just checked and it really is r15-2054-g1e3aa9c9278db6. Thanks for the tip, Andrew. Cc-ing richi. Though I must add that on the machine where I just ran the benchmarks (Zen 4) the slowdown is only ~3%.
While it might be interesting to investigate why making unaligned loads and stores costed faster than aligned ones the fix will be not restoring behavior to before the change. Given it's with LTO and only 3% tracking it down will be difficult. Note the change was backported to all affected branches.
Should I leave this bug open or close it, then? What do you think, Richard?
Let's keep it open as non-regression with amended Summary.