* config/h8300/h8300.md: Add comments about peephole2's.

From-SVN: r78921

gcc/ChangeLog

+2004-03-04  Kazu Hirata  <kazu@cs.umass.edu>
+
+	* config/h8300/h8300.md: Add comments about peephole2's.
+
 2004-03-04  Steven Bosscher  <stevenb@suse.de>
 
 	* i386.h (TARGET_CPU_DEFAULT_nocona): Fix value.

gcc/config/h8300/h8300.md

@@ -4373,8 +4373,15 @@
 ;;
 ;; ---- 65535                       geu/ltu mov.w
 
-;; For a small constant, it is cheaper to actually do the subtraction
-;; and then test the register.
+;; Transform
+;;
+;;	cmp.l	#1,er0
+;;	beq	.L1
+;;
+;; into
+;;
+;;	dec.l	#1,er0
+;;	beq	.L1
 
 (define_peephole2
   [(set (cc0)
@@ -4399,6 +4406,16 @@
 		      (pc)))]
   "operands[4] = GEN_INT (- INTVAL (operands[1]));")
 
+;; Transform
+;;
+;;	cmp.l	#65536,er0
+;;	beq	.L1
+;;
+;; into
+;;
+;;	dec.l	#1,e0
+;;	beq	.L1
+
 (define_peephole2
   [(set (cc0)
 	(compare (match_operand:SI 0 "register_operand" "")
@@ -4425,9 +4442,16 @@
 		      (pc)))]
   "operands[4] = GEN_INT (- INTVAL (operands[1]));")
 
-;; For certain (in)equality comparisons against a constant, we can
-;; XOR the register with the constant, and test the register against
-;; 0.
+;; Transform
+;;
+;;	cmp.l	#100,er0
+;;	beq	.L1
+;;
+;; into
+;;
+;;	xor.b	#100,er0
+;;	mov.l	er0,er0
+;;	beq	.L1
 
 (define_peephole2
   [(set (cc0)
@@ -4456,6 +4480,17 @@
 		      (pc)))]
   "")
 
+;; Transform
+;;
+;;	cmp.l	#-100,er0
+;;	beq	.L1
+;;
+;; into
+;;
+;;	xor.b	#99,er0
+;;	not.l	er0
+;;	beq	.L1
+
 (define_peephole2
   [(set (cc0)
 	(compare (match_operand:SI 0 "register_operand" "")
@@ -4484,6 +4519,17 @@
 		      (pc)))]
   "operands[4] = GEN_INT (INTVAL (operands[1]) ^ -1);")
 
+;; Transform
+;;
+;;	cmp.l	#-2147483648,er0
+;;	beq	.L1
+;;
+;; into
+;;
+;;	rotl.l	er0
+;;	dec.l	#1,er0
+;;	beq	.L1
+
 (define_peephole2
   [(set (cc0)
 	(compare (match_operand:SI 0 "register_operand" "")
@@ -4829,10 +4875,19 @@
 				const0_rtx);
 })
 
-;; For constants like -1, -2, 1, 2, it is still cheaper to make a copy
-;; of the register being tested, do the subtraction on the copy, and
-;; then test the copy.  We avoid this transformation if we see more
-;; than one copy of the same compare insn.
+;; Transform
+;;
+;;	cmp.l	#1,er0
+;;	beq	.L1
+;;
+;; into
+;;
+;;	mov.l	er0,er1
+;;	dec.l	#1,er1
+;;	beq	.L1
+
+;; We avoid this transformation if we see more than one copy of the
+;; same compare insn.
 
 (define_peephole2
   [(match_scratch:SI 4 "r")