[dev.power64] cmd/9g: introduce ginscon2 for CMP/CMPU, use ginscon to ADD constants

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://golang.org/cl/125170043

src/cmd/9g/cgen.c

@@ -690,8 +690,7 @@ agenr(Node *n, Node *a, Node *res)
 					n1.xoffset = Array_nel;
 					regalloc(&n4, n1.type, N);
 					gmove(&n1, &n4);
-					nodconst(&n2, types[TUINT64], v);
-					gins(optoas(OCMP, types[TUINT64]), &n4, &n2);
+					ginscon2(optoas(OCMP, types[TUINT64]), &n4, v);
 					regfree(&n4);
 					p1 = gbranch(optoas(OGT, types[TUINT64]), T, +1);
 					ginscall(panicindex, 0);
@@ -706,8 +705,7 @@ agenr(Node *n, Node *a, Node *res)
 			}
 
 			if (v*w != 0) {
-				nodconst(&n2, types[tptr], v*w);
-				gins(optoas(OADD, types[tptr]), &n2, &n3);
+				ginscon(optoas(OADD, types[tptr]), v*w, &n3);
 			}
 			*a = n3;
 			break;

src/cmd/9g/gg.h

@@ -87,6 +87,7 @@ Node*	nodarg(Type*, int);
 void	nodreg(Node*, Type*, int);
 void	nodindreg(Node*, Type*, int);
 void	ginscon(int, vlong, Node*);
+void	ginscon2(int, Node*, vlong);
 void	buildtxt(void);
 Plist*	newplist(void);
 int	isfat(Type*);

src/cmd/9g/gsubr.c

@@ -562,6 +562,40 @@ ginscon(int as, vlong c, Node *n2)
 	gins(as, &n1, n2);
 }
 
+/*
+ * generate
+ *	as n, $c (CMP/CMPU)
+ */
+void
+ginscon2(int as, Node *n2, vlong c)
+{
+	Node n1, ntmp;
+
+	nodconst(&n1, types[TINT64], c);
+
+	switch(as) {
+	default:
+		fatal("ginscon2");
+	case ACMP:
+		if(-BIG <= c && c <= BIG) {
+			gins(as, n2, &n1);
+			return;
+		}
+		break;
+	case ACMPU:
+		if(0 <= c && c <= 2*BIG) {
+			gins(as, n2, &n1);
+			return;
+		}
+		break;
+	}
+	// MOV n1 into register first
+	regalloc(&ntmp, types[TINT64], N);
+	gins(AMOVD, &n1, &ntmp);
+	gins(as, n2, &ntmp);
+	regfree(&ntmp);
+}
+
 #define	CASE(a,b)	(((a)<<16)|((b)<<0))
 /*c2go int CASE(int, int); */