https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84071
--- Comment #6 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> They are always written but have an undefined value. Adding 2 8-bit values
> results in a 9-bit value with WORD_REGISTER_OPERATIONS.
If they have an undefined value, then WORD_REGISTER_OPERATIONS must not be
defined for ARM. Here's the definition:
-- Macro: WORD_REGISTER_OPERATIONS
Define this macro to 1 if operations between registers with
integral mode smaller than a word are always performed on the
entire register. Most RISC machines have this property and most
CISC machines do not.
If the 8-bit addition is not performed on the entire 32-bit register, then this
is not a WORD_REGISTER_OPERATIONS target.
