diff --git a/llvm/include/llvm/CodeGen/RegisterClassInfo.h b/llvm/include/llvm/CodeGen/RegisterClassInfo.h
--- a/llvm/include/llvm/CodeGen/RegisterClassInfo.h
+++ b/llvm/include/llvm/CodeGen/RegisterClassInfo.h
@@ -56,7 +56,7 @@
   // Used only to determine if an update for CalleeSavedAliases is necessary.
   SmallVector<MCPhysReg, 16> LastCalleeSavedRegs;
 
-  // Map register alias to the callee saved Register.
+  // Map regunit to the callee saved Register.
   SmallVector<MCPhysReg, 4> CalleeSavedAliases;
 
   // Indicate if a specified callee saved register be in the allocation order
@@ -113,12 +113,16 @@
   }
 
   /// getLastCalleeSavedAlias - Returns the last callee saved register that
-  /// overlaps PhysReg, or NoRegister if Reg doesn't overlap a
+  /// overlaps PhysReg, or NoRegister if PhysReg doesn't overlap a
   /// CalleeSavedAliases.
   MCRegister getLastCalleeSavedAlias(MCRegister PhysReg) const {
-    if (PhysReg.id() < CalleeSavedAliases.size())
-      return CalleeSavedAliases[PhysReg];
-    return MCRegister::NoRegister;
+    MCRegister CSR;
+    for (MCRegUnitIterator UI(PhysReg, TRI); UI.isValid(); ++UI) {
+      CSR = CalleeSavedAliases[*UI];
+      if (CSR)
+        break;
+    }
+    return CSR;
   }
 
   /// Get the minimum register cost in RC's allocation order.
diff --git a/llvm/lib/CodeGen/RegisterClassInfo.cpp b/llvm/lib/CodeGen/RegisterClassInfo.cpp
--- a/llvm/lib/CodeGen/RegisterClassInfo.cpp
+++ b/llvm/lib/CodeGen/RegisterClassInfo.cpp
@@ -80,10 +80,10 @@
     LastCalleeSavedRegs.clear();
     // Build a CSRAlias map. Every CSR alias saves the last
     // overlapping CSR.
-    CalleeSavedAliases.assign(TRI->getNumRegs(), 0);
+    CalleeSavedAliases.assign(TRI->getNumRegUnits(), 0);
     for (const MCPhysReg *I = CSR; *I; ++I) {
-      for (MCRegAliasIterator AI(*I, TRI, true); AI.isValid(); ++AI)
-        CalleeSavedAliases[*AI] = *I;
+      for (MCRegUnitIterator UI(*I, TRI); UI.isValid(); ++UI)
+        CalleeSavedAliases[*UI] = *I;
       LastCalleeSavedRegs.push_back(*I);
     }
 
@@ -150,7 +150,7 @@
     uint8_t Cost = RegCosts[PhysReg];
     MinCost = std::min(MinCost, Cost);
 
-    if (CalleeSavedAliases[PhysReg] &&
+    if (getLastCalleeSavedAlias(PhysReg) &&
         !STI.ignoreCSRForAllocationOrder(*MF, PhysReg))
       // PhysReg aliases a CSR, save it for later.
       CSRAlias.push_back(PhysReg);