[Bug target/91635] wrong code at -O2 with __builtin_add_overflow() and shifts

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91635

--- Comment #24 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(clobber of a match_operand I mean, sigh).