https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110921
--- Comment #7 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to 罗勇刚(Yonggang Luo) from comment #6)
> MSVC also added, clang seems have optimization issue, but MSVC doesn't have
> that
No, I think what clang does is correct,
f(int, int): # @f(int, int)
test edi, edi ----------- when source operand is zero.
je .LBB0_2
rep bsf eax, edi
ret
.LBB0_2:
mov eax, 32
ret
The key difference between TZCNT and BSF instruction is that TZCNT provides
operand size as output when source operand is zero while in the case of BSF
instruction, if source operand is zero, the content of destination operand are
undefined.
https://godbolt.org/z/s74dfdWP4
