runtime: add test for go function argument scanning

Derived	from Naoki's reproducer.

Update #29362

Change-Id: I1cbd33b38a2f74905dbc22c5ecbad4a87a24bdd1
Reviewed-on: https://go-review.googlesource.com/c/156122
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

test/fixedbugs/issue29362.go

@@ -0,0 +1,42 @@
+// run
+
+// Copyright 2018 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.
+
+// Verify that we don't consider a Go'd function's
+// arguments as pointers when they aren't.
+
+package main
+
+import (
+	"unsafe"
+)
+
+var badPtr uintptr
+
+var sink []byte
+
+func init() {
+	// Allocate large enough to use largeAlloc.
+	b := make([]byte, 1<<16-1)
+	sink = b // force heap allocation
+	//  Any space between the object and the end of page is invalid to point to.
+	badPtr = uintptr(unsafe.Pointer(&b[len(b)-1])) + 1
+}
+
+var throttle = make(chan struct{}, 10)
+
+func noPointerArgs(a, b, c, d uintptr) {
+	sink = make([]byte, 4096)
+	<-throttle
+}
+
+func main() {
+	const N = 1000
+	for i := 0; i < N; i++ {
+		throttle <- struct{}{}
+		go noPointerArgs(badPtr, badPtr, badPtr, badPtr)
+		sink = make([]byte, 4096)
+	}
+}