cmd/gc: fix inlining bug with local variables.

Fixes #4323.

R=rsc, lvd, golang-dev
CC=golang-dev
https://golang.org/cl/6815061

src/cmd/gc/inl.c

@@ -556,6 +556,8 @@ mkinlcall1(Node **np, Node *fn)
 	for(ll = dcl; ll; ll=ll->next)
 		if(ll->n->op == ONAME) {
 			ll->n->inlvar = inlvar(ll->n);
+			// Typecheck because inlvar is not necessarily a function parameter.
+			typecheck(&ll->n->inlvar, Erv);
 			ninit = list(ninit, nod(ODCL, ll->n->inlvar, N));  // otherwise gen won't emit the allocations for heapallocs
 			if (ll->n->class == PPARAMOUT)  // we rely on the order being correct here
 				inlretvars = list(inlretvars, ll->n->inlvar);

test/fixedbugs/issue4323.go

@@ -0,0 +1,31 @@
+// compile
+
+// Copyright 2012 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 4323: inlining of functions with local variables
+// forgets to typecheck the declarations in the inlined copy.
+
+package main
+
+type reader struct {
+	C chan T
+}
+
+type T struct{ C chan []byte }
+
+var r = newReader()
+
+func newReader() *reader { return new(reader) }
+
+func (r *reader) Read(n int) ([]byte, error) {
+	req := T{C: make(chan []byte)}
+	r.C <- req
+	return <-req.C, nil
+}
+
+func main() {
+	s, err := r.Read(1)
+	_, _ = s, err
+}