https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106471
--- Comment #6 from Linus Torvalds <torva...@linux-foundation.org> --- Ahh, crossed comments. (In reply to Andrew Pinski from comment #3) > The xor is due to X86_TUNE_AVOID_FALSE_DEP_FOR_BMI setting: > > /* X86_TUNE_AVOID_FALSE_DEP_FOR_BMI: Avoid false dependency > for bit-manipulation instructions. */ Ahh, ok, so it is indeed for that false dependency for old cpus. Intel claims that's only for POPCNT on more recent CPU's. But yes, the same thing definitely happened for BSF for much older cores (ie pre-TZCNT).
