https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110921
--- Comment #8 from 罗勇刚(Yonggang Luo) <luoyonggang at gmail dot com> --- (In reply to Hongtao.liu from comment #7) > No, I think what clang does is correct, Thanks, yeap, according to https://github.com/llvm/llvm-project/issues/64477 I think clang did it well. GCC also needs handling the following code properly ```c #ifdef _MSC_VER #include <intrin.h> __forceinline void unreachable() {__assume(0);} #else #include <x86intrin.h> inline __attribute__((always_inline)) void unreachable() { #if defined(__INTEL_COMPILER) __assume(0); #else __builtin_unreachable(); #endif } #endif int f(int a) { if (a == 0) { unreachable(); } return _tzcnt_u32 (a); } ``` According to https://godbolt.org/z/T9axzaPqj gcc with `-O2 -mbmi -m32` option compiled to ```asm f(int): xor eax, eax tzcnt eax, DWORD PTR [esp+4] ret ``` There is a redundant xor instrunction, Without `-mbmi` option, gcc can not compile and all other three compiler can compile. This issue still make sense, gcc can fixes it in Clang's way
