https://gcc.gnu.org/bugzilla/show_bug.cgi?id=29776
--- Comment #22 from Steinar H. Gunderson <steinar+gcc at gunderson dot no> --- Yes; I had a project recently where I won 15% overall performance (!) by using an asm statement with bsf instead of ffsll(). (This skipped both the sign extension and the check for zero; my argument could never be zero, due to a loop condition, but GCC didn't manage to remove the check nevertheless.)
