https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97503
--- Comment #7 from Uroš Bizjak <ubizjak at gmail dot com> --- (In reply to Uroš Bizjak from comment #6) > (In reply to LIU Hao from comment #4) > > Are there any reasons why this was not done for 64? > > (https://gcc.godbolt.org/z/7vddPdxaP) > > There is zero-extension from the result of __builtin_clzll that confuses > optimizers. Actually, sign-extension, but the result is never sign-extended.
