cmd/gc: disallow pointer constants
Fixes #7760.
LGTM=iant
R=iant, remyoudompheng
CC=golang-codereviews
https://golang.org/cl/130720043
diff --git a/test/fixedbugs/issue7760.go b/test/fixedbugs/issue7760.go
new file mode 100644
index 0000000..cccae48
--- /dev/null
+++ b/test/fixedbugs/issue7760.go
@@ -0,0 +1,25 @@
+// errorcheck
+
+// Copyright 2014 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 pointers can't be used as constants.
+
+package main
+
+import "unsafe"
+
+type myPointer unsafe.Pointer
+
+const _ = unsafe.Pointer(uintptr(1)) // ERROR "is not (a )?constant"
+const _ = myPointer(uintptr(1)) // ERROR "is not (a )?constant"
+
+const _ = (*int)(unsafe.Pointer(uintptr(1))) // ERROR "is not (a )?constant"
+const _ = (*int)(myPointer(uintptr(1))) // ERROR "is not (a )?constant"
+
+const _ = uintptr(unsafe.Pointer(uintptr(1))) // ERROR "is not (a )?constant"
+const _ = uintptr(myPointer(uintptr(1))) // ERROR "is not (a )?constant"
+
+const _ = []byte("") // ERROR "is not (a )?constant"
+const _ = []rune("") // ERROR "is not (a )?constant"
