Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -263,25 +263,39 @@
     CarryIn = 1;
   }
 
-  APInt PossibleSumZero = ~LHSKnownZero + ~RHSKnownZero + CarryIn;
-  APInt PossibleSumOne = LHSKnownOne + RHSKnownOne + CarryIn;
+  // Flip the known zeroes so we can add them.
+  LHSKnownZero.flipAllBits();
+  RHSKnownZero.flipAllBits();
+
+  // Create a sum for the known zeros.
+  KnownZero |= CarryIn;
+  KnownZero += LHSKnownZero;
+  KnownZero += RHSKnownZero;
+
+  // Restore the known zeroes and flip the sum.
+  LHSKnownZero.flipAllBits();
+  RHSKnownZero.flipAllBits();
+  KnownZero.flipAllBits();
+
+  // Create a sum for the known ones.
+  KnownOne |= CarryIn;
+  KnownOne += RHSKnownOne;
+  KnownOne += LHSKnownOne;
 
   // Compute known bits of the carry.
-  APInt CarryKnownZero = ~(PossibleSumZero ^ LHSKnownZero ^ RHSKnownZero);
-  APInt CarryKnownOne = PossibleSumOne ^ LHSKnownOne ^ RHSKnownOne;
+  APInt CarryKnownZero = KnownZero ^ LHSKnownZero ^ RHSKnownZero;
+  APInt CarryKnownOne = KnownOne ^ LHSKnownOne ^ RHSKnownOne;
 
   // Compute set of known bits (where all three relevant bits are known).
-  APInt LHSKnown = LHSKnownZero | LHSKnownOne;
-  APInt RHSKnown = RHSKnownZero | RHSKnownOne;
-  APInt CarryKnown = CarryKnownZero | CarryKnownOne;
-  APInt Known = LHSKnown & RHSKnown & CarryKnown;
-
-  assert((PossibleSumZero & Known) == (PossibleSumOne & Known) &&
+  APInt Known = std::move(CarryKnownZero) | std::move(CarryKnownOne);
+  Known &= LHSKnownZero | LHSKnownOne;
+  Known &= RHSKnownZero | RHSKnownOne;
+  assert((~KnownZero & Known) == (KnownOne & Known) &&
          "known bits of sum differ");
 
-  // Compute known bits of the result.
-  KnownZero = ~PossibleSumOne & Known;
-  KnownOne = PossibleSumOne & Known;
+  // Bits of sums are only known if all input bits were known.
+  KnownZero &= Known;
+  KnownOne &= Known;
 
   // Are we still trying to solve for the sign bit?
   if (!Known.isNegative()) {