I was having a look at PR71636 and added the following pattern to match.pd:
x & ((1U << b) - 1) -> x & ~(~0U << b)
However the transform is useful only if the target supports "andnot"
As pointed out by Marc in PR for -march=core2, lhs generates worse
code than rhs,
so we shouldn't do the transform if target doesn't support andnot insn.
(perhaps we could do the reverse transform for target not supporting andnot?)
However it seems andnot isn't a standard pattern name, so am not sure
how to check
if target supports andnot insn ?