diff --git a/utils/TableGen/CodeGenTarget.h b/utils/TableGen/CodeGenTarget.h
index ef46b6c6185..c7cc77ccd41 100644
--- a/utils/TableGen/CodeGenTarget.h
+++ b/utils/TableGen/CodeGenTarget.h
@@ -19,6 +19,7 @@
 
 #include "CodeGenRegisters.h"
 #include "CodeGenInstruction.h"
+#include <algorithm>
 #include <iosfwd>
 #include <map>
 
@@ -110,19 +111,54 @@ public:
   }
   
   /// getRegisterClassForRegister - Find the register class that contains the
-  /// specified physical register.  If there register exists in multiple
-  /// register classes or is not in a register class, return null.
+  /// specified physical register.  If the register is not in a register
+  /// class, return null. If the register is in multiple classes, and the
+  /// classes have a superset-subset relationship and the same set of
+  /// types, return the superclass.  Otherwise return null.
   const CodeGenRegisterClass *getRegisterClassForRegister(Record *R) const {
     const std::vector<CodeGenRegisterClass> &RCs = getRegisterClasses();
     const CodeGenRegisterClass *FoundRC = 0;
     for (unsigned i = 0, e = RCs.size(); i != e; ++i) {
       const CodeGenRegisterClass &RC = RegisterClasses[i];
       for (unsigned ei = 0, ee = RC.Elements.size(); ei != ee; ++ei) {
-        if (R == RC.Elements[ei]) {
-          if (FoundRC) return 0;  // In multiple RC's
+        if (R != RC.Elements[ei])
+          continue;
+
+        // If a register's classes have different types, return null.
+        if (FoundRC && RC.getValueTypes() != FoundRC->getValueTypes())
+          return 0;
+
+        // If this is the first class that contains the register,
+        // make a note of it and go on to the next class.
+        if (!FoundRC) {
           FoundRC = &RC;
           break;
         }
+
+        std::vector<Record *> Elements(RC.Elements);
+        std::vector<Record *> FoundElements(FoundRC->Elements);
+        std::sort(Elements.begin(), Elements.end());
+        std::sort(FoundElements.begin(), FoundElements.end());
+
+        // Check to see if the previously found class that contains
+        // the register is a subclass of the current class. If so,
+        // prefer the superclass.
+        if (std::includes(Elements.begin(), Elements.end(),
+                          FoundElements.begin(), FoundElements.end())) {
+          FoundRC = &RC;
+          break;
+        }
+
+        // Check to see if the previously found class that contains
+        // the register is a superclass of the current class. If so,
+        // prefer the superclass.
+        if (std::includes(FoundElements.begin(), FoundElements.end(),
+                          Elements.begin(), Elements.end()))
+          break;
+
+        // Multiple classes, and neither is a superclass of the other.
+        // Return null.
+        return 0;
       }
     }
     return FoundRC;