cmd/compile: make HasHeapPointer recursive

Currently (*Type).HasHeapPointer only ignores pointers go:notinheap
types if the type itself is a pointer to a go:notinheap type. However,
if it's some other type that contains pointers where all of those
pointers are go:notinheap, it will conservatively return true. As a
result, we'll use write barriers where they aren't needed, for example
calling typedmemmove instead of just memmove on structs that contain
only go:notinheap pointers.

Fix this by making HasHeapPointer walk the whole type looking for
pointers that aren't marked go:notinheap.

Change-Id: Ib8c6abf6f7a20f34969d1d402c5498e0b990be59
Reviewed-on: https://go-review.googlesource.com/73412
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/test/notinheap3.go b/test/notinheap3.go
new file mode 100644
index 0000000000..e01c7a0a82
--- /dev/null
+++ b/test/notinheap3.go
@@ -0,0 +1,45 @@
+// errorcheck -+ -0 -l -d=wb
+
+// Copyright 2016 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.
+
+// Test write barrier elimination for notinheap.
+
+package p
+
+type t1 struct {
+	x *nih
+	y [1024]byte // Prevent write decomposition
+}
+
+type t2 struct {
+	x *ih
+	y [1024]byte
+}
+
+//go:notinheap
+type nih struct {
+	x uintptr
+}
+
+type ih struct { // In-heap type
+	x uintptr
+}
+
+var (
+	v1 t1
+	v2 t2
+)
+
+func f() {
+	// Test direct writes
+	v1.x = nil // no barrier
+	v2.x = nil // ERROR "write barrier"
+}
+
+func g() {
+	// Test aggregate writes
+	v1 = t1{x: nil} // no barrier
+	v2 = t2{x: nil} // ERROR "write barrier"
+}