[Bug tree-optimization/114269] New: [14 Regression] Multiple 3-27% exec time regressions of 434.zeusmp since r14-9193-ga0b1798042d033

["pheeck at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114269

            Bug ID: 114269
           Summary: [14 Regression] Multiple 3-27% exec time regressions
                    of 434.zeusmp since r14-9193-ga0b1798042d033
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pheeck at gcc dot gnu.org
                CC: rguenth at gcc dot gnu.org
            Blocks: 26163
  Target Milestone: ---
              Host: x86_64-linux
            Target: x86_64-linux

Our LNT instance has detected that runtime of benchmark 434.zeusmp from the
SPEC 2006 suite regressed on x86_64 machines on most configurations by 3-27%.

Some examples:

AMD Zen2 -Ofast -march=native -flto (22% regression)
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=289.80.0

Intel Skylake -Ofast -march=native PGO (11% regression)
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=791.80.0

AMD Zen4 -O2 -flto PGO (7% regression)
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=960.80.0

AMD Zen2 -Ofast -march=native (26% regression)
https://lnt.opensuse.org/db_default/v4/SPEC/graph?plot.0=301.80.0

I have bisected these configurations to the same commit
- AMD Zen2 -Ofast
- AMD Zen2 -Ofast -march=native -flto PGO
- AMD Zen4 -O2 -flto PGO

the commit is r14-9193-ga0b1798042d033 (Richard Biener:
tree-optimization/114074 - CHREC multiplication and undefined overflow).

I haven't seen this speedup on our Aarch64 machine. I have seen it on our Intel
machine though, so this is not an AMD-specific issue.

There is another PR where a SPEC slowed down that was also bisected to the same
commit: pr114238. Maybe these two PRs are actually the same bug.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26163
[Bug 26163] [meta-bug] missed optimization in SPEC (2k17, 2k and 2k6 and 95)