Revert a part of r223583, for now. It seems causing different emission between stage2(gcc-clang) and stage3 clang. Investigating.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223624 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/InstructionSimplify.cpp

@@ -1476,11 +1476,6 @@ static Value *simplifyUnsignedRangeCheck(ICmpInst *ZeroICmp,
     return UnsignedICmp;
   }
 
-  // X < Y && Y == 0  -->  false
-  if (UnsignedPred == ICmpInst::ICMP_ULT && EqPred == ICmpInst::ICMP_EQ &&
-      IsAnd)
-    return getFalse(UnsignedICmp->getType());
-
   return nullptr;
 }