https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104357
Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2022-02-02 Component|target |tree-optimization Ever confirmed|0 |1 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- This will get GCC closer to what clang/LLVM produces: unsigned char stbi__clamp(int x) { int t = x; if ((unsigned)x > 255) { if (x < 0) t = 0; else if (x > 255) t = -1; } return t; } ---- CUT ---- The zero-extends are due to the cast not being outside of the csel and the RTL level is not really good at cross bb optimizations. The gimple level looks like: <bb 2> [local count: 1073741824]: x.0_1 = (unsigned int) x_3(D); if (x.0_1 > 255) goto <bb 3>; [50.00%] else goto <bb 4>; [50.00%] <bb 3> [local count: 536870913]: _7 = x_3(D) >= 0; _6 = (unsigned char) _7; _8 = -_6; goto <bb 5>; [100.00%] <bb 4> [local count: 536870913]: _4 = (unsigned char) x_3(D); <bb 5> [local count: 1073741824]: # _2 = PHI <_8(3), _4(4)> return _2; Which in theory could be improved to the what I gave above. The gimple level has no knowledge of the rtl/target level that to do - in unsigned, you need to a zero extend still.