cmd/gc: add way to specify 'noescape' for extern funcs
A new comment directive //go:noescape instructs the compiler
that the following external (no body) func declaration should be
treated as if none of its arguments escape to the heap.
Fixes #4099.
R=golang-dev, dave, minux.ma, daniel.morsing, remyoudompheng, adg, agl, iant
CC=golang-dev
https://golang.org/cl/7289048
diff --git a/test/fixedbugs/issue4099.go b/test/fixedbugs/issue4099.go
new file mode 100644
index 0000000..89392bf
--- /dev/null
+++ b/test/fixedbugs/issue4099.go
@@ -0,0 +1,26 @@
+// errorcheck -0 -m
+
+// 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.
+
+// Check go:noescape annotations.
+
+package p
+
+// The noescape comment only applies to the next func,
+// which must not have a body.
+
+//go:noescape
+
+func F1([]byte)
+
+func F2([]byte)
+
+func G() {
+ var buf1 [10]byte
+ F1(buf1[:]) // ERROR "buf1 does not escape"
+
+ var buf2 [10]byte // ERROR "moved to heap: buf2"
+ F2(buf2[:]) // ERROR "buf2 escapes to heap"
+}
