cmd/gc: allow registerization of temporaries created by inlining.

Names beginning with a dot are ignored by optimizers.

R=rsc, lvd, golang-dev, dave
CC=golang-dev
https://golang.org/cl/7098049

src/cmd/gc/dcl.c

@@ -638,7 +638,7 @@ funcargs(Node *nt)
 
 		if(n->left == N) {
 			// give it a name so escape analysis has nodes to work with
-			snprint(namebuf, sizeof(namebuf), ".anon%d", gen++);
+			snprint(namebuf, sizeof(namebuf), "~anon%d", gen++);
 			n->left = newname(lookup(namebuf));
 			n->left->orig = N;  // signal that the original was absent
 
@@ -653,7 +653,7 @@ funcargs(Node *nt)
 			*nn = *n->left;
 			n->left = nn;
 			
-			snprint(namebuf, sizeof(namebuf), ".anon%d", gen++);
+			snprint(namebuf, sizeof(namebuf), "~anon%d", gen++);
 			n->left->sym = lookup(namebuf);
 		}
 

src/cmd/gc/inl.c

@@ -699,7 +699,7 @@ retvar(Type *t, int i)
 {
 	Node *n;
 
-	snprint(namebuf, sizeof(namebuf), ".r%d", i);
+	snprint(namebuf, sizeof(namebuf), "~r%d", i);
 	n = newname(lookup(namebuf));
 	n->type = t->type;
 	n->class = PAUTO;