gcc does not reduce to call result if called function is not static in -O2 (will do with -O2) clang and msvc does it also in -O2 regardless of the function beeing static or not
can someone explain to me why the -O2 optimizer is not able(allowed) to reduce this small sample the same way as clang/msvc? x86-64 gcc 10.2 and trunk -O2: https://godbolt.org/z/r3GM57 x86-64 clang trunk and 11.0.0 -O2: https://godbolt.org/z/8hqbz5 x64 msvc v19.27 -O2: https://godbolt.org/z/nv3rWq code to reproduce --------------------------- #include <cstdint> // part of run length encoding... static void v32(uint32_t v_, uint8_t* b_, int& s_) { if (v_ <= 0x0000007FU) { s_ = 1; b_[0] = (uint8_t)v_; return; } if (v_ <= 0x00003FFFU) { s_ = 2; b_[1] = (uint8_t)(v_ & 0x7F); b_[0] = (uint8_t)((v_ >> 7) | 0x80); return; } s_ = 3; b_[2] = (uint8_t)(v_ & 0x7F); b_[1] = (uint8_t)((v_ >> 7) | 0x80); b_[0] = (uint8_t)((v_ >> 14) | 0x80); return; } int test(uint32_t v_) { uint8_t b[3]{}; int s=0; v32(v_, b, s); return s+b[0]+b[1]+b[2]; } int main(int argc, char** argv) { return test(1337); // results in 197 // clang reduces the call down to 197 regardless of test beeing static or not //main: # @main // mov eax, 197 // ret // gcc reduces the call only if test is static //main: // mov edi, 1337 // jmp test(unsigned int) } ------------------------------------
