[Bug middle-end/126774] New: wi::bitreverse/wi::bswap should use __builtin_* if supported and precision is known at compile time.

kaelfandrew at gmail dot com via Gcc-bugs <[email protected]> Mon, 10 Aug 2026 17:54:15 +0000

Newsgroups	gmane.comp.gcc.bugs
Message-ID	<[email protected]/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126774

            Bug ID: 126774
           Summary: wi::bitreverse/wi::bswap should use __builtin_* if
                    supported and precision is known at compile time.
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kaelfandrew at gmail dot com
  Target Milestone: ---

GCC does not optimize wi::bitreverse_large/wi::bswap_large to use
__builtin_bswap/__builtin_bitreverse if precision is known.

Use STAGE0_CXX_HAS_BUILTIN(bitreverse8) to detect if compiler
supports __builtin_bitreverse8.