cmd/compile, syscall: add //go:uintptrescapes comment, and use it

This new comment can be used to declare that the uintptr arguments to a
function may be converted from pointers, and that those pointers should
be considered to escape. This is used for the Call methods in
dll_windows.go that take uintptr arguments, because they call Syscall.

We can't treat these functions as we do syscall.Syscall, because unlike
Syscall they may cause the stack to grow. For Syscall we can assume that
stack arguments can remain on the stack, but for these functions we need
them to escape.

Fixes #16035.

Change-Id: Ia0e5b4068c04f8d303d95ab9ea394939f1f57454
Reviewed-on: https://go-review.googlesource.com/24551
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/test/uintptrescapes2.go b/test/uintptrescapes2.go
new file mode 100644
index 0000000000..7ff676db14
--- /dev/null
+++ b/test/uintptrescapes2.go
@@ -0,0 +1,31 @@
+// errorcheck -0 -m -live
+
+// 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 escape analysis and liveness inferred for uintptrescapes functions.
+
+package p
+
+import (
+	"unsafe"
+)
+
+//go:uintptrescapes
+//go:noinline
+func F1(a uintptr) {} // ERROR "escaping uintptr"
+
+//go:uintptrescapes
+//go:noinline
+func F2(a ...uintptr) {} // ERROR "escaping ...uintptr" "live at entry" "a does not escape"
+
+func G() {
+	var t int // ERROR "moved to heap"
+	F1(uintptr(unsafe.Pointer(&t))) // ERROR "live at call to F1: autotmp" "&t escapes to heap"
+}
+
+func H() {
+	var v int // ERROR "moved to heap"
+	F2(0, 1, uintptr(unsafe.Pointer(&v)), 2) // ERROR "live at call to newobject: autotmp" "live at call to F2: autotmp" "escapes to heap"
+}