https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112758
--- Comment #12 from Segher Boessenkool <segher at gcc dot gnu.org> --- (In reply to Eric Botcazou from comment #11) > > It says those upper bits are well-defined, i.e. whatever MD pattern is used > > for it eventually will emit machine code that has the exact same result for > > those upper bits. > > No, that's not true, the set of "register operations" is restricted. Who what where? That is not how it is documented. There is word_register_operation_p as a bandaid to make it *somewhat* work, added decades later, but it still won't fly :-( Different parts of the compiler think it has much more stringent semantics btw.
