https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78103
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|target |middle-end
--- Comment #3 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Richard Biener from comment #2)
> There isn't a find-last-set builtin thus this is a target (or RTL
> optimization) issue. I believe find-last-set is also computed by ffs (x &
> -x) so that might be a more canonical way to express this on GIMPLE?
Please try with -mlzcnt that expands the builtin to a single insn. But looking
at a _t.optimized dump the RTL/target backend just expands what tree optimizers
push to the backend.
Probably a __builtin_fls needs to be introduced, to enable middle-end to fold
these constructs.
This is a middle-end issue, backend can't do anything there...
