xtensa: Optimize boolean evaluation when SImode EQ/NE to zero if TARGET_MINMAX

xtensa: Optimize boolean evaluation when SImode EQ/NE to zero if TARGET_MINMAX

This patch optimizes the boolean evaluation for equality to 0 in SImode
using the MINU (Minimum Value Unsigned) machine instruction available
when TARGET_MINMAX is configured, for example, (x != 0) to MINU(x, 1)
and (x == 0) to (MINU(x, 1) ^ 1).

    /* example */
    int test0(int x) {
      return x == 0;
    }
    int test1(int x) {
      return x != 0;
    }

    ;; before
    test0:
	mov.n	a10, a2
	movi.n	a9, 1
	movi.n	a2, 0
	moveqz	a2, a9, a10
	ret.n
    test1:
	mov.n	a10, a2
	movi.n	a9, 1
	movi.n	a2, 0
	movnez	a2, a9, a10
	ret.n

    ;; after (prereq. TARGET_MINMAX)
    test0:
	movi.n	a9, 1
	minu	a2, a2, a9
	xor	a2, a2, a9
	ret.n
    test1:
	movi.n	a9, 1
	minu	a2, a2, a9
	ret.n

gcc/ChangeLog:

	* config/xtensa/xtensa.cc (xtensa_expand_scc):
	Add code for particular constants (only 0 and INT_MIN for now)
	for EQ/NE boolean evaluation in SImode.
	* config/xtensa/xtensa.md (*eqne_INT_MIN): Remove because its
	implementation has been integrated into the above.