xtensa: Optimize "bitwise AND with imm1" followed by "branch if (not) equal to imm2"

xtensa: Optimize "bitwise AND with imm1" followed by "branch if (not) equal to imm2"

This patch enhances the effectiveness of the previously posted one:
"xtensa: Optimize bitwise AND operation with some specific forms of constants".

    /* example */
    extern void foo(int);
    void test(int a) {
      if ((a & (-1U << 8)) == (128 << 8))  /* 0 or one of "b4const" */
        foo(a);
    }

    ;; before
	.global	test
    test:
	movi	a3, -0x100
	movi.n	a4, 1
	and	a3, a2, a3
	slli	a4, a4, 15
	bne	a3, a4, .L3
	j.l	foo, a9
    .L1:
	ret.n

    ;; after
	.global test
    test:
	srli	a3, a2, 8
	bnei	a3, 128, .L1
	j.l	foo, a9
    .L1:
	ret.n

gcc/ChangeLog:

	* config/xtensa/xtensa.md
	(*masktrue_const_pow2_minus_one, *masktrue_const_negative_pow2,
	*masktrue_const_shifted_mask): If the immediate for bitwise AND is
	represented as '-(1 << N)', decrease the lower bound of N from 12
	to 1.  And the other immediate for conditional branch is now no
	longer limited to zero, but also one of some positive integers.
	Finally, remove the checks of some conditions, because the comparison
	expressions that don't satisfy such checks are determined as
	compile-time constants and thus will be optimized away before
	RTL expansion.