From 19564e3d83c9c3cdf908005c91bad13d26b5cedf Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Tue, 30 May 2006 18:04:34 +0000
Subject: [PATCH] When a priority_queue is empty, the behavior of top()
 operator is non-deterministic. Returns NULL when it's empty!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28560 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp b/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
index c9aa18a342e..ad8ed5aaf97 100644
--- a/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
+++ b/lib/CodeGen/SelectionDAG/ScheduleDAGList.cpp
@@ -356,6 +356,7 @@ public:
     }
     
     SUnit *pop() {
+      if (empty()) return NULL;
       SUnit *V = Queue.top();
       Queue.pop();
       return V;