https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118115
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Last reconfirmed| |2024-12-19
Summary|Missed Optimization: |Missed Optimization:
|Failure to Elide Branch |Failure to Elide Branch
|When Copying Overlapping |When Copying Overlapping
|Union Members |Union Members from
| |arguments to returns
Blocks| |101926
Depends on| |61810
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So GCC is in this case is doing:
`b = is_ab ? b : 0` Which is coming from init-regs which means it might only be
an issue from argument and return case.
Do you have a better benchmark instead of this micro-benchmark where the
conditional move will show up?
This is just a bad artifact of how GCC handles arguments/returns and even
uninitialized registers usage (PR 61810).
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61810
[Bug 61810] init-regs.c papers over issues elsewhere
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101926
[Bug 101926] [meta-bug] struct/complex/other argument passing and return should
be improved
