cmd/cgo, runtime: recognize unsafe.Pointer(&s[0]) in cgo pointer checks

It's fairly common to call cgo functions with conversions to
unsafe.Pointer or other C types.  Apply the simpler checking of address
expressions when possible when the address expression occurs within a
type conversion.

Change-Id: I5187d4eb4d27a6542621c396cad9ee4b8647d1cd
Reviewed-on: https://go-review.googlesource.com/18391
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/misc/cgo/errors/ptr.go b/misc/cgo/errors/ptr.go
index 1534601524..0dd291f5ed 100644
--- a/misc/cgo/errors/ptr.go
+++ b/misc/cgo/errors/ptr.go
@@ -107,6 +107,16 @@ var ptrTests = []ptrTest{
 		fail:    false,
 	},
 	{
+		// Passing the address of a slice of an array that is
+		// an element in a struct, with a type conversion.
+		name:    "slice-ok-3",
+		c:       `void f(void* p) {}`,
+		imports: []string{"unsafe"},
+		support: `type S struct { p *int; a [4]byte }`,
+		body:    `i := 0; p := &S{p:&i}; s := p.a[:]; C.f(unsafe.Pointer(&s[0]))`,
+		fail:    false,
+	},
+	{
 		// Passing the address of a static variable with no
 		// pointers doesn't matter.
 		name:    "varok",