misched: add a hook for custom DAG postprocessing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163915 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineScheduler.cpp b/lib/CodeGen/MachineScheduler.cpp
index 330ec56..d7ecec4 100644
--- a/lib/CodeGen/MachineScheduler.cpp
+++ b/lib/CodeGen/MachineScheduler.cpp
@@ -484,6 +484,8 @@
 void ScheduleDAGMI::schedule() {
   buildDAGWithRegPressure();
 
+  postprocessDAG();
+
   DEBUG(for (unsigned su = 0, e = SUnits.size(); su != e; ++su)
           SUnits[su].dumpAll(this));
 
@@ -522,6 +524,13 @@
   initRegPressure();
 }
 
+/// Apply each ScheduleDAGMutation step in order.
+void ScheduleDAGMI::postprocessDAG() {
+  for (unsigned i = 0, e = Mutations.size(); i < e; ++i) {
+    Mutations[i]->apply(this);
+  }
+}
+
 /// Identify DAG roots and setup scheduler queues.
 void ScheduleDAGMI::initQueues() {
   // Initialize the strategy before modifying the DAG.