diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 73c3c47..1e62b9d 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -680,14 +680,14 @@
   if (match(Op0, m_Zero())) {
     // 0 - X -> 0 if the sub is NUW.
     if (isNUW)
-      return Op0;
+      return Constant::getNullValue(Op0->getType());
 
     KnownBits Known = computeKnownBits(Op1, Q.DL, 0, Q.AC, Q.CxtI, Q.DT);
     if (Known.Zero.isMaxSignedValue()) {
       // Op1 is either 0 or the minimum signed value. If the sub is NSW, then
       // Op1 must be 0 because negating the minimum signed value is undefined.
       if (isNSW)
-        return Op0;
+        return Constant::getNullValue(Op0->getType());
 
       // 0 - X -> X if X is 0 or the minimum signed value.
       return Op1;
@@ -799,12 +799,9 @@
     return C;
 
   // X * undef -> 0
-  if (match(Op1, m_Undef()))
-    return Constant::getNullValue(Op0->getType());
-
   // X * 0 -> 0
-  if (match(Op1, m_Zero()))
-    return Op1;
+  if (match(Op1, m_CombineOr(m_Undef(), m_Zero())))
+    return Constant::getNullValue(Op0->getType());
 
   // X * 1 -> X
   if (match(Op1, m_One()))
@@ -888,7 +885,7 @@
   // 0 / X -> 0
   // 0 % X -> 0
   if (match(Op0, m_Zero()))
-    return Op0;
+    return Constant::getNullValue(Op0->getType());
 
   // X / X -> 1
   // X % X -> 0
@@ -1147,7 +1144,7 @@
 
   // 0 shift by X -> 0
   if (match(Op0, m_Zero()))
-    return Op0;
+    return Constant::getNullValue(Op0->getType());
 
   // X shift by 0 -> X
   if (match(Op1, m_Zero()))
@@ -1689,7 +1686,7 @@
 
   // X & 0 = 0
   if (match(Op1, m_Zero()))
-    return Op1;
+    return Constant::getNullValue(Op0->getType());
 
   // X & -1 = X
   if (match(Op1, m_AllOnes()))
@@ -3068,8 +3065,7 @@
   Type *ITy = GetCompareTy(LHS); // The return type.
 
   // icmp X, X -> true/false
-  // X icmp undef -> true/false.  For example, icmp ugt %X, undef -> false
-  // because X could be 0.
+  // icmp X, undef -> true/false because undef could be X.
   if (LHS == RHS || isa<UndefValue>(RHS))
     return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));