Use a utility from MathExtras to clarify a check and avoid undefined behavior. Based on patch by Ahmed Charles.

llvm-svn: 141829

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -1679,7 +1679,7 @@ void SelectionDAGBuilder::visitBitTestHeader(BitTestBlock &B,
     UsePtrType = true;
   else {
     for (unsigned i = 0, e = B.Cases.size(); i != e; ++i)
-      if ((uint64_t)((int64_t)B.Cases[i].Mask >> VT.getSizeInBits()) + 1 >= 2) {
+      if (!isUIntN(VT.getSizeInBits(), B.Cases[i].Mask)) {
         // Switch table case range are encoded into series of masks.
         // Just use pointer type, it's guaranteed to fit.
         UsePtrType = true;