diff --git a/lib/CodeGen/CriticalAntiDepBreaker.cpp b/lib/CodeGen/CriticalAntiDepBreaker.cpp
index e3746a9..9d48665 100644
--- a/lib/CodeGen/CriticalAntiDepBreaker.cpp
+++ b/lib/CodeGen/CriticalAntiDepBreaker.cpp
@@ -34,6 +34,9 @@
   TRI(MF.getTarget().getRegisterInfo()),
   AllocatableSet(TRI->getAllocatableSet(MF))
 {
+  Classes.reserve(TRI->getNumRegs());
+  KillIndices.reserve(TRI->getNumRegs());
+  DefIndices.reserve(TRI->getNumRegs());
 }
 
 CriticalAntiDepBreaker::~CriticalAntiDepBreaker() {
@@ -41,8 +44,7 @@
 
 void CriticalAntiDepBreaker::StartBlock(MachineBasicBlock *BB) {
   // Clear out the register class data.
-  std::fill(Classes, array_endof(Classes),
-            static_cast<const TargetRegisterClass *>(0));
+  Classes.clear();
 
   // Initialize the indices to indicate that no registers are live.
   const unsigned BBSize = BB->size();
diff --git a/lib/CodeGen/CriticalAntiDepBreaker.h b/lib/CodeGen/CriticalAntiDepBreaker.h
index 5406300..62ef72a 100644
--- a/lib/CodeGen/CriticalAntiDepBreaker.h
+++ b/lib/CodeGen/CriticalAntiDepBreaker.h
@@ -25,6 +25,7 @@
 #include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/SmallSet.h"
 #include <map>
+#include <vector>
 
 namespace llvm {
 class TargetInstrInfo;
@@ -46,19 +47,18 @@
     /// corresponding value is null. If the register is live but used in
     /// multiple register classes, the corresponding value is -1 casted to a
     /// pointer.
-    const TargetRegisterClass *
-      Classes[TargetRegisterInfo::FirstVirtualRegister];
+    std::vector<const TargetRegisterClass *> Classes;
 
     /// RegRegs - Map registers to all their references within a live range.
     std::multimap<unsigned, MachineOperand *> RegRefs;
 
     /// KillIndices - The index of the most recent kill (proceding bottom-up),
     /// or ~0u if the register is not live.
-    unsigned KillIndices[TargetRegisterInfo::FirstVirtualRegister];
+    std::vector<unsigned> KillIndices;
 
     /// DefIndices - The index of the most recent complete def (proceding bottom
     /// up), or ~0u if the register is live.
-    unsigned DefIndices[TargetRegisterInfo::FirstVirtualRegister];
+    std::vector<unsigned> DefIndices;
 
     /// KeepRegs - A set of registers which are live and cannot be changed to
     /// break anti-dependencies.