Index: llvm/trunk/include/llvm/ADT/APInt.h
===================================================================
--- llvm/trunk/include/llvm/ADT/APInt.h
+++ llvm/trunk/include/llvm/ADT/APInt.h
@@ -240,11 +240,12 @@
   APInt(unsigned numBits, uint64_t val, bool isSigned = false)
       : BitWidth(numBits), VAL(0) {
     assert(BitWidth && "bitwidth too small");
-    if (isSingleWord())
+    if (isSingleWord()) {
       VAL = val;
-    else
+      clearUnusedBits();
+    } else {
       initSlowCase(val, isSigned);
-    clearUnusedBits();
+    }
   }
 
   /// \brief Construct an APInt of numBits width, initialized as bigVal[].
Index: llvm/trunk/lib/Support/APInt.cpp
===================================================================
--- llvm/trunk/lib/Support/APInt.cpp
+++ llvm/trunk/lib/Support/APInt.cpp
@@ -81,6 +81,7 @@
   if (isSigned && int64_t(val) < 0)
     for (unsigned i = 1; i < getNumWords(); ++i)
       pVal[i] = -1ULL;
+  clearUnusedBits();
 }
 
 void APInt::initSlowCase(const APInt& that) {