https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113210
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Or maybe just a bug in the PLUS_EXPR folding? The code sets NITERSM1 to (short unsigned int) (a.0_1 + 255) + 1 > 256 ? ~(short unsigned int) (a.0_1 + 255) : 0 and then fold_build2s PLUS_EXPR of that and 1 and somehow it folds to 1, that doesn't sound right to me. Now, when folding the + 1 addition just with the second operand, i.e. ~(short unsigned int) (a.0_1 + 255) it correctly folds into -(short unsigned int) (a.0_1 + 255) and obviously the second one to 1. There is also the /* (X + 1) > Y ? -X : 1 simplifies to X >= Y ? -X : 1 when X is unsigned, as when X + 1 overflows, X is -1, so -X == 1. */ (simplify (cond (gt (plus @0 integer_onep) @1) (negate @0) integer_onep@2) (if (TYPE_UNSIGNED (type)) (cond (ge @0 @1) (negate @0) @2))) match.pd rule, but that I'd think should just fold the whole thing to: (short unsigned int) (a.0_1 + 255) >= 256 ? -(short unsigned int) (a.0_1 + 255) : 1 Though, a.0_1 is unsigned char, so (short unsigned int) (a.0_1 + 255) + 1 > 256 is actually never true. So guess the folding is correct.
