Don't cse LdCns

Because in php, constants aren't.

hphp/runtime/vm/translator/hopt/ir.h

@@ -283,7 +283,7 @@ O(LdClsCtx,                     D(Cls), S(Ctx),                            C) \
 O(LdClsCctx,                    D(Cls), S(Cctx),                           C) \
 O(LdClsCns,                     DParam, CStr CStr,                         C) \
 O(LookupClsCns,                 DParam, CStr CStr,           E|Refs|Er|N|Mem) \
-O(LdCns,                        DParam, CStr,                              C) \
+O(LdCns,                        DParam, CStr,                             NF) \
 O(LookupCns,                    DParam, CStr,                E|Refs|Er|N|Mem) \
 O(LdClsMethodCache,         D(FuncCls), SUnk,              N|C|E|Refs|Er|Mem) \
 O(LdClsMethodFCache,        D(FuncCtx), C(Cls) CStr S(Obj,Cls,Ctx), N|C|E|Er) \

hphp/test/slow/constant/cns-autoload.php

@@ -0,0 +1,13 @@
+<?php
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+function def() { define('FOO', 1); }
+function show($a,$b) { var_dump($a,$b); }
+function test() {
+  show(FOO, FOO);
+}
+
+fb_autoload_map(array('constant' => array(),
+                      'failure' => 'def'), "");
+
+test();

hphp/test/slow/constant/cns-autoload.php.expect

@@ -0,0 +1,2 @@
+int(1)
+int(1)