cmd/gc: fix issue with method wrappers not having escape analysis run on them.

Escape analysis needs the right curfn value on a dclfunc node, otherwise it will not analyze the function.
When generating method value wrappers, we forgot to set the curfn correctly.

Fixes #5753.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/10383048

src/cmd/gc/closure.c

@@ -280,7 +280,7 @@ typecheckpartialcall(Node *fn, Node *sym)
 static Node*
 makepartialcall(Node *fn, Type *t0, Node *meth)
 {
-	Node *ptr, *n, *fld, *call, *xtype, *xfunc, *cv;
+	Node *ptr, *n, *fld, *call, *xtype, *xfunc, *cv, *savecurfn;
 	Type *rcvrtype, *basetype, *t;
 	NodeList *body, *l, *callargs, *retargs;
 	char *p;
@@ -305,12 +305,16 @@ makepartialcall(Node *fn, Type *t0, Node *meth)
 		return sym->def;
 	sym->flags |= SymUniq;
 	
+	savecurfn = curfn;
+	curfn = N;
+
 	xtype = nod(OTFUNC, N, N);
 	i = 0;
 	l = nil;
 	callargs = nil;
 	ddd = 0;
 	xfunc = nod(ODCLFUNC, N, N);
+	curfn = xfunc;
 	for(t = getinargx(t0)->type; t; t = t->down) {
 		snprint(namebuf, sizeof namebuf, "a%d", i++);
 		n = newname(lookup(namebuf));
@@ -385,6 +389,7 @@ makepartialcall(Node *fn, Type *t0, Node *meth)
 	typecheck(&xfunc, Etop);
 	sym->def = xfunc;
 	xtop = list(xtop, xfunc);
+	curfn = savecurfn;
 
 	return xfunc;
 }

test/fixedbugs/issue5753.go

@@ -0,0 +1,29 @@
+// run
+
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// issue 5753: bad typecheck info causes escape analysis to
+// not run on method thunks.
+
+package main
+
+type Thing struct{}
+
+func (t *Thing) broken(s string) []string {
+	foo := [1]string{s}
+	return foo[:]
+}
+
+func main() {
+	t := &Thing{}
+
+	f := t.broken
+	s := f("foo")
+	_ = f("bar")
+	if s[0] != "foo" {
+		panic(`s[0] != "foo"`)
+	}
+	
+}