diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 7faf19fd72f..04ccc77b6bb 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -585,7 +585,7 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
     break;
   case ISD::ZERO_EXTEND:
     if (Operand.getValueType() == VT) return Operand;   // noop extension
-    if (OpOpcode == ISD::ZERO_EXTEND)
+    if (OpOpcode == ISD::ZERO_EXTEND)   // (zext (zext x)) -> (zext x)
       return getNode(ISD::ZERO_EXTEND, VT, Operand.Val->getOperand(0));
     break;
   case ISD::TRUNCATE:
@@ -1025,6 +1025,18 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,SDOperand N1,
         return N1;
     }
 
+    // If we are extending the result of a setcc, and we already know the
+    // contents of the top bits, eliminate the extension.
+    if (N1.getOpcode() == ISD::SETCC)
+      switch (TLI.getSetCCResultContents()) {
+      case TargetLowering::UndefinedSetCCResult: break;
+      case TargetLowering::ZeroOrOneSetCCResult:
+        if (Opcode == ISD::ZERO_EXTEND_INREG) return N1;
+        break;
+      case TargetLowering::ZeroOrNegativeOneSetCCResult:
+        if (Opcode == ISD::SIGN_EXTEND_INREG) return N1;
+        break;
+      }
     break;
   }