[Bug middle-end/66872] fold a & ((1 << b) - 1) to a & ~(-1 << b)

[bonzini at gnu dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66872

--- Comment #2 from Paolo Bonzini <bonzini at gnu dot org> ---
> left shift of negative value is undefined behavior in C

It's not in any of GCC's intermediate representations, though.