Index: lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -227,6 +227,12 @@
 
     // Compute the KnownZero/KnownOne bits to simplify things downstream.
     computeKnownBits(I, KnownZero, KnownOne, Depth, CxtI);
+
+    // If the client is only demanding bits that we know, return the known
+    // constant.
+    if ((DemandedMask & (KnownZero|KnownOne)) == DemandedMask)
+      return Constant::getIntegerValue(VTy, KnownOne);
+
     return nullptr;
   }