xtensa: Make instruction cost estimation for size more accurate

xtensa: Make instruction cost estimation for size more accurate

Until now, we applied COSTS_N_INSNS() (multiplying by 4) after dividing
the instruction length by 3, so we couldn't express the difference less
than modulo 3 in insn cost for size (e.g. 11 Bytes and 12 bytes cost the
same).

This patch fixes that.

;; 2 bytes
addi.n	a2, a2, -1	; cost 3

;; 3 bytes
addmi	a2, a2, 1024	; cost 4

;; 4 bytes
movi.n	a3, 80		; cost 5
bnez.n	a2, a3, .L4

;; 5 bytes
srli	a2, a3, 1	; cost 7
add.n	a2, a2, a2

;; 6 bytes
ssai	8		; cost 8
src	a4, a2, a3

:: 3 + 4 bytes
l32r	a2, .L5		; cost 9

;; 11 bytes		; cost 15
;; 12 bytes		; cost 16

gcc/ChangeLog:

	* config/xtensa/xtensa.cc (xtensa_insn_cost):
	Let insn cost for size be obtained by applying COSTS_N_INSNS()
	to instruction length and then dividing by 3.