misched: Recompute priority queue when DFSResults are updated.

This was found by MSVC10's STL debug mode on a test from the test suite. Sadly
std::is_heap isn't standard so there is no way to assert this without writing
our own heap verify, which looks like overkill to me.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168885 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/MachineScheduler.cpp

@@ -2117,6 +2117,8 @@ public:
   virtual void registerRoots() {
     DFSResult.compute(ReadyQ);
     ScheduledTrees.resize(DFSResult.getNumSubtrees());
+    // Restore the heap in ReadyQ with the updated DFS results.
+    std::make_heap(ReadyQ.begin(), ReadyQ.end(), Cmp);
   }
 
   /// Implement MachineSchedStrategy interface.