6g: avoid too-large immediate constants

R=ken2
CC=golang-dev
https://golang.org/cl/2566042

src/cmd/6g/cgen.c

@@ -537,9 +537,7 @@ agen(Node *n, Node *res)
 				gmove(&n1, &n3);
 			}
 
-			nodconst(&n2, types[tptr], v*w);
-			gins(optoas(OADD, types[tptr]), &n2, &n3);
-
+			ginscon(optoas(OADD, types[tptr]), v*w, &n3);
 			gmove(&n3, res);
 			regfree(&n3);
 			break;
@@ -596,8 +594,7 @@ agen(Node *n, Node *res)
 			p1->from.index = p1->from.type;
 			p1->from.type = p1->to.type + D_INDIR;
 		} else {
-			nodconst(&n1, t, w);
-			gins(optoas(OMUL, t), &n1, &n2);
+			ginscon(optoas(OMUL, t), w, &n2);
 			gins(optoas(OADD, types[tptr]), &n2, &n3);
 			gmove(&n3, res);
 		}
@@ -621,10 +618,8 @@ agen(Node *n, Node *res)
 			fatal("agen: bad ONAME class %#x", n->class);
 		}
 		cgen(n->heapaddr, res);
-		if(n->xoffset != 0) {
-			nodconst(&n1, types[TINT64], n->xoffset);
-			gins(optoas(OADD, types[tptr]), &n1, res);
-		}
+		if(n->xoffset != 0)
+			ginscon(optoas(OADD, types[tptr]), n->xoffset, res);
 		break;
 
 	case OIND:
@@ -633,10 +628,8 @@ agen(Node *n, Node *res)
 
 	case ODOT:
 		agen(nl, res);
-		if(n->xoffset != 0) {
-			nodconst(&n1, types[TINT64], n->xoffset);
-			gins(optoas(OADD, types[tptr]), &n1, res);
-		}
+		if(n->xoffset != 0)
+			ginscon(optoas(OADD, types[tptr]), n->xoffset, res);
 		break;
 
 	case ODOTPTR:
@@ -653,8 +646,7 @@ agen(Node *n, Node *res)
 				gins(ATESTB, nodintconst(0), &n1);
 				regfree(&n1);
 			}
-			nodconst(&n1, types[TINT64], n->xoffset);
-			gins(optoas(OADD, types[tptr]), &n1, res);
+			ginscon(optoas(OADD, types[tptr]), n->xoffset, res);
 		}
 		break;
 	}

src/cmd/6g/gg.h

@@ -123,6 +123,7 @@ Node*	nodarg(Type*, int);
 void	nodreg(Node*, Type*, int);
 void	nodindreg(Node*, Type*, int);
 void	gconreg(int, vlong, int);
+void	ginscon(int, vlong, Node*);
 void	buildtxt(void);
 Plist*	newplist(void);
 int	isfat(Type*);

src/cmd/6g/ggen.c

@@ -1292,10 +1292,8 @@ slicearray:
 	if(smallintconst(&nodes[2]) && smallintconst(&nodes[4])) {
 		v = mpgetfix(nodes[2].val.u.xval) *
 			mpgetfix(nodes[4].val.u.xval);
-		if(v != 0) {
-			nodconst(&n1, types[tptr], v);
-			gins(optoas(OADD, types[tptr]), &n1, &nodes[0]);
-		}
+		if(v != 0)
+			ginscon(optoas(OADD, types[tptr]), v, &nodes[0]);
 	} else {
 		regalloc(&n1, types[tptr], &nodes[2]);
 		gmove(&nodes[2], &n1);
@@ -1409,10 +1407,8 @@ sliceslice:
 		gins(optoas(OAS, types[tptr]), &n2, &n1);
 		v = mpgetfix(nodes[1].val.u.xval) *
 			mpgetfix(nodes[3].val.u.xval);
-		if(v != 0) {
-			nodconst(&n2, types[tptr], v);
-			gins(optoas(OADD, types[tptr]), &n2, &n1);
-		}
+		if(v != 0)
+			ginscon(optoas(OADD, types[tptr]), v, &n1);
 	} else {
 		gmove(&nodes[1], &n1);
 		if(!smallintconst(&nodes[3]) || mpgetfix(nodes[3].val.u.xval) != 1)

src/cmd/6g/gsubr.c

@@ -430,11 +430,33 @@ fatal("shouldnt be used");
 void
 gconreg(int as, vlong c, int reg)
 {
-	Node n1, n2;
+	Node nr;
+
+	nodreg(&nr, types[TINT64], reg);
+	ginscon(as, c, &nr);
+}
+
+/*
+ * generate
+ *	as $c, n
+ */
+void
+ginscon(int as, vlong c, Node *n2)
+{
+	Node n1, ntmp;
 
 	nodconst(&n1, types[TINT64], c);
-	nodreg(&n2, types[TINT64], reg);
-	gins(as, &n1, &n2);
+
+	if(as != AMOVQ && (c < -1LL<<31 || c >= 1LL<<31)) {
+		// cannot have 64-bit immediokate in ADD, etc.
+		// instead, MOV into register first.
+		regalloc(&ntmp, types[TINT64], N);
+		gins(AMOVQ, &n1, &ntmp);
+		gins(as, &ntmp, n2);
+		regfree(&ntmp);
+		return;
+	}
+	gins(as, &n1, n2);
 }
 
 #define	CASE(a,b)	(((a)<<16)|((b)<<0))