diff --git a/lib/CodeGen/AggressiveAntiDepBreaker.cpp b/lib/CodeGen/AggressiveAntiDepBreaker.cpp
index 54026b6..4008a6a 100644
--- a/lib/CodeGen/AggressiveAntiDepBreaker.cpp
+++ b/lib/CodeGen/AggressiveAntiDepBreaker.cpp
@@ -281,9 +281,9 @@
 
 /// AntiDepEdges - Return in Edges the anti- and output- dependencies
 /// in SU that we want to consider for breaking.
-static void AntiDepEdges(SUnit *SU, std::vector<SDep*>& Edges) {
+static void AntiDepEdges(const SUnit *SU, std::vector<const SDep*>& Edges) {
   SmallSet<unsigned, 4> RegSet;
-  for (SUnit::pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
+  for (SUnit::const_pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
        P != PE; ++P) {
     if ((P->getKind() == SDep::Anti) || (P->getKind() == SDep::Output)) {
       unsigned Reg = P->getReg();
@@ -297,14 +297,14 @@
 
 /// CriticalPathStep - Return the next SUnit after SU on the bottom-up
 /// critical path.
-static SUnit *CriticalPathStep(SUnit *SU) {
-  SDep *Next = 0;
+static const SUnit *CriticalPathStep(const SUnit *SU) {
+  const SDep *Next = 0;
   unsigned NextDepth = 0;
   // Find the predecessor edge with the greatest depth.
   if (SU != 0) {
-    for (SUnit::pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
+    for (SUnit::const_pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
          P != PE; ++P) {
-      SUnit *PredSU = P->getSUnit();
+      const SUnit *PredSU = P->getSUnit();
       unsigned PredLatency = P->getLatency();
       unsigned PredTotalLatency = PredSU->getDepth() + PredLatency;
       // In the case of a latency tie, prefer an anti-dependency edge over
@@ -703,9 +703,9 @@
 /// ScheduleDAG and break them by renaming registers.
 ///
 unsigned AggressiveAntiDepBreaker::BreakAntiDependencies(
-                              std::vector<SUnit>& SUnits,
-                              MachineBasicBlock::iterator& Begin,
-                              MachineBasicBlock::iterator& End,
+                              const std::vector<SUnit>& SUnits,
+                              MachineBasicBlock::iterator Begin,
+                              MachineBasicBlock::iterator End,
                               unsigned InsertPosIndex) {
   unsigned *KillIndices = State->GetKillIndices();
   unsigned *DefIndices = State->GetDefIndices();
@@ -720,20 +720,21 @@
   RenameOrderType RenameOrder;
 
   // ...need a map from MI to SUnit.
-  std::map<MachineInstr *, SUnit *> MISUnitMap;
+  std::map<MachineInstr *, const SUnit *> MISUnitMap;
   for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
-    SUnit *SU = &SUnits[i];
-    MISUnitMap.insert(std::pair<MachineInstr *, SUnit *>(SU->getInstr(), SU));
+    const SUnit *SU = &SUnits[i];
+    MISUnitMap.insert(std::pair<MachineInstr *, const SUnit *>(SU->getInstr(),
+                                                               SU));
   }
 
   // Track progress along the critical path through the SUnit graph as
   // we walk the instructions. This is needed for regclasses that only
   // break critical-path anti-dependencies.
-  SUnit *CriticalPathSU = 0;
+  const SUnit *CriticalPathSU = 0;
   MachineInstr *CriticalPathMI = 0;
   if (CriticalPathSet.any()) {
     for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
-      SUnit *SU = &SUnits[i];
+      const SUnit *SU = &SUnits[i];
       if (!CriticalPathSU ||
           ((SU->getDepth() + SU->Latency) >
            (CriticalPathSU->getDepth() + CriticalPathSU->Latency))) {
@@ -774,8 +775,8 @@
 
     // The dependence edges that represent anti- and output-
     // dependencies that are candidates for breaking.
-    std::vector<SDep*> Edges;
-    SUnit *PathSU = MISUnitMap[MI];
+    std::vector<const SDep *> Edges;
+    const SUnit *PathSU = MISUnitMap[MI];
     AntiDepEdges(PathSU, Edges);
 
     // If MI is not on the critical path, then we don't rename
@@ -793,7 +794,7 @@
     if (!MI->isKill()) {
       // Attempt to break each anti-dependency...
       for (unsigned i = 0, e = Edges.size(); i != e; ++i) {
-        SDep *Edge = Edges[i];
+        const SDep *Edge = Edges[i];
         SUnit *NextSU = Edge->getSUnit();
 
         if ((Edge->getKind() != SDep::Anti) &&
@@ -837,7 +838,7 @@
           // Also, if there are dependencies on other SUnits with the
           // same register as the anti-dependency, don't attempt to
           // break it.
-          for (SUnit::pred_iterator P = PathSU->Preds.begin(),
+          for (SUnit::const_pred_iterator P = PathSU->Preds.begin(),
                  PE = PathSU->Preds.end(); P != PE; ++P) {
             if (P->getSUnit() == NextSU ?
                 (P->getKind() != SDep::Anti || P->getReg() != AntiDepReg) :
@@ -846,7 +847,7 @@
               break;
             }
           }
-          for (SUnit::pred_iterator P = PathSU->Preds.begin(),
+          for (SUnit::const_pred_iterator P = PathSU->Preds.begin(),
                  PE = PathSU->Preds.end(); P != PE; ++P) {
             if ((P->getSUnit() == NextSU) && (P->getKind() != SDep::Anti) &&
                 (P->getKind() != SDep::Output)) {
diff --git a/lib/CodeGen/AggressiveAntiDepBreaker.h b/lib/CodeGen/AggressiveAntiDepBreaker.h
index a62d68c..506d43e 100644
--- a/lib/CodeGen/AggressiveAntiDepBreaker.h
+++ b/lib/CodeGen/AggressiveAntiDepBreaker.h
@@ -142,9 +142,9 @@
     /// path
     /// of the ScheduleDAG and break them by renaming registers.
     ///
-    unsigned BreakAntiDependencies(std::vector<SUnit>& SUnits,
-                                   MachineBasicBlock::iterator& Begin,
-                                   MachineBasicBlock::iterator& End,
+    unsigned BreakAntiDependencies(const std::vector<SUnit>& SUnits,
+                                   MachineBasicBlock::iterator Begin,
+                                   MachineBasicBlock::iterator End,
                                    unsigned InsertPosIndex);
 
     /// Observe - Update liveness information to account for the current
diff --git a/lib/CodeGen/AntiDepBreaker.h b/lib/CodeGen/AntiDepBreaker.h
index 3ee30c6..086b757 100644
--- a/lib/CodeGen/AntiDepBreaker.h
+++ b/lib/CodeGen/AntiDepBreaker.h
@@ -39,9 +39,9 @@
   /// basic-block region and break them by renaming registers. Return
   /// the number of anti-dependencies broken.
   ///
-  virtual unsigned BreakAntiDependencies(std::vector<SUnit>& SUnits,
-                                MachineBasicBlock::iterator& Begin,
-                                MachineBasicBlock::iterator& End,
+  virtual unsigned BreakAntiDependencies(const std::vector<SUnit>& SUnits,
+                                MachineBasicBlock::iterator Begin,
+                                MachineBasicBlock::iterator End,
                                 unsigned InsertPosIndex) =0;
   
   /// Observe - Update liveness information to account for the current
diff --git a/lib/CodeGen/CriticalAntiDepBreaker.cpp b/lib/CodeGen/CriticalAntiDepBreaker.cpp
index 7d3de89..759fbaa 100644
--- a/lib/CodeGen/CriticalAntiDepBreaker.cpp
+++ b/lib/CodeGen/CriticalAntiDepBreaker.cpp
@@ -143,13 +143,13 @@
 
 /// CriticalPathStep - Return the next SUnit after SU on the bottom-up
 /// critical path.
-static SDep *CriticalPathStep(SUnit *SU) {
-  SDep *Next = 0;
+static const SDep *CriticalPathStep(const SUnit *SU) {
+  const SDep *Next = 0;
   unsigned NextDepth = 0;
   // Find the predecessor edge with the greatest depth.
-  for (SUnit::pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
+  for (SUnit::const_pred_iterator P = SU->Preds.begin(), PE = SU->Preds.end();
        P != PE; ++P) {
-    SUnit *PredSU = P->getSUnit();
+    const SUnit *PredSU = P->getSUnit();
     unsigned PredLatency = P->getLatency();
     unsigned PredTotalLatency = PredSU->getDepth() + PredLatency;
     // In the case of a latency tie, prefer an anti-dependency edge over
@@ -326,18 +326,18 @@
 }
 
 unsigned CriticalAntiDepBreaker::
-BreakAntiDependencies(std::vector<SUnit>& SUnits,
-                      MachineBasicBlock::iterator& Begin,
-                      MachineBasicBlock::iterator& End,
+BreakAntiDependencies(const std::vector<SUnit>& SUnits,
+                      MachineBasicBlock::iterator Begin,
+                      MachineBasicBlock::iterator End,
                       unsigned InsertPosIndex) {
   // The code below assumes that there is at least one instruction,
   // so just duck out immediately if the block is empty.
   if (SUnits.empty()) return 0;
 
   // Find the node at the bottom of the critical path.
-  SUnit *Max = 0;
+  const SUnit *Max = 0;
   for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
-    SUnit *SU = &SUnits[i];
+    const SUnit *SU = &SUnits[i];
     if (!Max || SU->getDepth() + SU->Latency > Max->getDepth() + Max->Latency)
       Max = SU;
   }
@@ -357,7 +357,7 @@
 
   // Track progress along the critical path through the SUnit graph as we walk
   // the instructions.
-  SUnit *CriticalPathSU = Max;
+  const SUnit *CriticalPathSU = Max;
   MachineInstr *CriticalPathMI = CriticalPathSU->getInstr();
 
   // Consider this pattern:
@@ -429,8 +429,8 @@
     // the anti-dependencies in an instruction in order to be effective.
     unsigned AntiDepReg = 0;
     if (MI == CriticalPathMI) {
-      if (SDep *Edge = CriticalPathStep(CriticalPathSU)) {
-        SUnit *NextSU = Edge->getSUnit();
+      if (const SDep *Edge = CriticalPathStep(CriticalPathSU)) {
+        const SUnit *NextSU = Edge->getSUnit();
 
         // Only consider anti-dependence edges.
         if (Edge->getKind() == SDep::Anti) {
@@ -452,7 +452,7 @@
             // Also, if there are dependencies on other SUnits with the
             // same register as the anti-dependency, don't attempt to
             // break it.
-            for (SUnit::pred_iterator P = CriticalPathSU->Preds.begin(),
+            for (SUnit::const_pred_iterator P = CriticalPathSU->Preds.begin(),
                  PE = CriticalPathSU->Preds.end(); P != PE; ++P)
               if (P->getSUnit() == NextSU ?
                     (P->getKind() != SDep::Anti || P->getReg() != AntiDepReg) :
diff --git a/lib/CodeGen/CriticalAntiDepBreaker.h b/lib/CodeGen/CriticalAntiDepBreaker.h
index 9e8db02..cc42dd2 100644
--- a/lib/CodeGen/CriticalAntiDepBreaker.h
+++ b/lib/CodeGen/CriticalAntiDepBreaker.h
@@ -72,9 +72,9 @@
     /// path
     /// of the ScheduleDAG and break them by renaming registers.
     ///
-    unsigned BreakAntiDependencies(std::vector<SUnit>& SUnits,
-                                   MachineBasicBlock::iterator& Begin,
-                                   MachineBasicBlock::iterator& End,
+    unsigned BreakAntiDependencies(const std::vector<SUnit>& SUnits,
+                                   MachineBasicBlock::iterator Begin,
+                                   MachineBasicBlock::iterator End,
                                    unsigned InsertPosIndex);
 
     /// Observe - Update liveness information to account for the current