https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115756
Bug ID: 115756 Summary: default tuning for x86_64 produces shifts for `*240` Product: gcc Version: 15.0 Status: UNCONFIRMED Keywords: missed-optimization Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: pinskia at gcc dot gnu.org Target Milestone: --- Take: ``` unsigned long func(unsigned long x) { return x * 240; } ``` For most modern CPUs (I think), it is faster to use imul here instead of shifts/adds/sub. clang's default tuning uses imul even. -mtune=skylake, -mtune=znver[123], all produces imul. Note -mtune=lunarlake/arrowlake does not but maybe they are wrong. Split out from PR 115749 .