cmd/gc: steal escape analysis info when inlining

Usually, there is no esc info when inlining, but there will be when generating inlined wrapper functions.

If we don't use this information, we get invalid addresses on the stack.

Fixes #5056.

R=golang-dev, rsc
CC=golang-dev, remyoudompheng
https://golang.org/cl/7850045

src/cmd/gc/inl.c

@@ -797,6 +797,12 @@ inlvar(Node *var)
 	n->class = PAUTO;
 	n->used = 1;
 	n->curfn = curfn;   // the calling function, not the called one
+
+	// esc pass wont run if we're inlining into a iface wrapper
+	// luckily, we can steal the results from the target func
+	if(var->esc == EscHeap)
+		addrescapes(n);
+
 	curfn->dcl = list(curfn->dcl, n);
 	return n;
 }

test/fixedbugs/issue5056.go

+// 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 5056: escape analysis not applied to wrapper functions
+
+package main
+
+type Foo int16
+
+func (f Foo) Esc() *int{
+	x := int(f)
+	return &x
+}
+
+type iface interface {
+	Esc() *int
+}
+
+var bar, foobar *int
+
+func main() {
+	var quux iface
+	var x Foo
+	
+	quux = x
+	bar = quux.Esc()
+	foobar = quux.Esc()
+	if bar == foobar {
+		panic("bar == foobar")
+	}
+}