[Bug rtl-optimization/112758] [13/14 Regression] Inconsistent Bitwise AND Operation Result between int and long long int

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112758

--- Comment #4 from Segher Boessenkool <segher at gcc dot gnu.org> ---
WORD_REGISTER_OPERATIONS is extremely ill-defined.  Or, it is used for other
things than what it stands for, whichever way you want to look at it.

A backend that defines the macro to non-zero promises that for *any* operation
on any values in a smaller than full-register mode, the compiler can instead
do the operation in that full-register mode, and all the resulting bits will
be well-defined.  This is not true for most real non-trivial backends.

There is word_register_operation_p to filter out the most obvious and egregious
cases where WORD_REGISTER_OPERATIONS is just a foolish thing, but this function
isn't used nearly enough, and it doesn't filter out enough either.