simplify-rtx: Combine bitwise operations in more cases

simplify-rtx: Combine bitwise operations in more cases

This patch transforms RTL expressions of the form (subreg (not X)) into
(not (subreg X)) if the subreg is an operand of another binary logical
operation. This transformation can expose opportunities to combine more
logical operations.

For example, it improves the codegen of the following AArch64 NEON
intrinsics:
	vandq_s64(vreinterpretq_s64_s32(vmvnq_s32(a)),
		  vreinterpretq_s64_s32(b));
from:
	not     v0.16b, v0.16b
	and     v0.16b, v0.16b, v1.16b
to:
	bic     v0.16b, v1.16b, v0.16b

Regression tested on x86_64-linux-gnu, arm-linux-gnueabihf and
aarch64-linux-gnu.

gcc/ChangeLog:

	* simplify-rtx.cc (non_paradoxical_subreg_not_p): New function
	for pattern match of (subreg (not X)).
	(simplify_with_subreg_not): New function for simplification.