middle-end: Optimize (A&C)^(B&C) to (A^B)&C in simplify_rtx (take 3).

middle-end: Optimize (A&C)^(B&C) to (A^B)&C in simplify_rtx (take 3).

2020-06-29  Roger Sayle  <roger@nextmovesoftware.com>
gcc/ChangeLog:
	* simplify-rtx.c (simplify_distributive_operation): New function
	to un-distribute a binary operation of two binary operations.
	(X & C) ^ (Y & C) to (X ^ Y) & C, when C is simple (i.e. a constant).
	(simplify_binary_operation_1) <IOR, XOR, AND>: Call it from here
	when appropriate.
	(test_scalar_int_ops): New function for unit self-testing
	scalar integer transformations in simplify-rtx.c.
	(test_scalar_ops): Call test_scalar_int_ops for each integer mode.
	(simplify_rtx_c_tests): Call test_scalar_ops.