[InstCombine] Use pointer alignment in SimplifyDemandedBits

For parity with computeKnownBits(). This came up when adding a
consistency assertion.

llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

@@ -1022,6 +1022,11 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
   }
   }
 
+  if (V->getType()->isPointerTy()) {
+    Align Alignment = V->getPointerAlignment(DL);
+    Known.Zero.setLowBits(Log2(Alignment));
+  }
+
   // If the client is only demanding bits that we know, return the known
   // constant. We can't directly simplify pointers as a constant because of
   // pointer provenance.