xtensa: Optimize several boolean evaluations of EQ/NE against constant zero

xtensa: Optimize several boolean evaluations of EQ/NE against constant zero

An idiomatic implementation of boolean evaluation of whether a register is
zero or not in Xtensa is to assign 0 and 1 to the temporary and destination,
and then issue the MOV[EQ/NE]Z machine instruction
(See 8.3.2 Instruction Idioms, Xtensa ISA refman., p.599):

;; A2 = (A3 != 0) ? 1 : 0;
	movi.n	a9, 1
	movi.n	a2, 0
	movnez	a2, a9, a3  ;; if (A3 != 0) A2 = A9;

As you can see in the above idiom, if the source and destination are the
same register, a move instruction from the source to another temporary
register must be prepended:

;; A2 = (A2 == 0) ? 1 : 0;
	mov.n	a10, a2
	movi.n	a9, 1
	movi.n	a2, 0
	moveqz	a2, a9, a10  ;; if (A10 == 0) A2 = A9;

Fortunately, we can reduce the number of instructions and temporary
registers with a few tweaks:

;; A2 = (A3 != 0) ? 1 : 0;
	movi.n	a2, 1
	moveqz	a2, a3, a3  ;; if (A3 == 0) A2 = A3;

;; A2 = (A2 != 0) ? 1 : 0;
	movi.n	a9, 1
	movnez	a2, a9, a2  ;; if (A2 != 0) A2 = A9;

;; A2 = (A3 == 0) ? 1 : 0;
	movi.n	a2, -1
        moveqz	a2, a3, a3  ;; if (A3 == 0) A2 = A3;
        addi.n	a2, a2, 1

;; A2 = (A2 == 0) ? 1 : 0;
	movi.n	a9, -1
	movnez	a2, a9, a2  ;; if (A2 != 0) A2 = A9;
	addi.n	a2, a2, 1

Additionally, if TARGET_NSA is configured, the fact that it returns 32 iff
the source of the NSAU machine instruction is 0, otherwise less than, can be
used in boolean evaluation of EQ comparison.

;; A2 = (A3 == 0) ? 1 : 0;
	nsau	a2, a3      ;; Source and destination can be the same register
	srli	a2, a2, 5

Furthermore, this patch also saves one instruction when determining whether
the ANDing with mask values in which 1s are lined up from the upper or lower
bit end (for example, 0xFFE00000 or 0x003FFFFF) is 0 or not.

gcc/ChangeLog:

	* config/xtensa/xtensa.cc (xtensa_expand_scc):
	Revert the changes from the last patch, as the work in the RTL
	expansion pass is too far to determine the physical registers.
	* config/xtensa/xtensa.md (*eqne_INT_MIN): Ditto.
	(eq_zero_NSA, eqne_zero, *eqne_zero_masked_bits): New patterns.