https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84071
--- Comment #10 from Eric Botcazou <ebotcazou at gcc dot gnu.org> --- > The addition is performed on the full 32-bit register, so this obviously > means that the top 24 bits have an undefined value. Not if the entire registers have a defined value before the addition. The point of WORD_REGISTER_OPERATIONS is the following: you have a pair of SImode registers with known values and you do a QImode addition on them. If the macro is defined, then the compiler considers that the result has a defined value in SImode. In any case, that's not really the issue here and I'll just fix the combiner.
