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

[zsojka at seznam dot cz]

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

--- Comment #4 from Zdenek Sojka <zsojka at seznam dot cz> ---
(In reply to Jakub Jelinek from comment #3)
> Looks like a backend bug to me.
...
> fixes this, but I don't have a way to test riscv, plus the backend has
> several similar problems elsewhere.

I can provide several other testcases where code using shifts is miscompiled.