Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4841,18 +4841,23 @@
   case Intrinsic::usub_with_overflow:
   case Intrinsic::ssub_with_overflow:
     // X - X -> { 0, false }
-    if (Op0 == Op1)
+    // X - undef -> { 0, false } for undef = X.
+    // undef - X -> { 0, false } for undef = X.
+    if (Op0 == Op1 || isa<UndefValue>(Op0) || isa<UndefValue>(Op1))
       return Constant::getNullValue(ReturnType);
-    // X - undef -> undef
-    // undef - X -> undef
-    if (isa<UndefValue>(Op0) || isa<UndefValue>(Op1))
-      return UndefValue::get(ReturnType);
     break;
   case Intrinsic::uadd_with_overflow:
   case Intrinsic::sadd_with_overflow:
-    // X + undef -> undef
-    if (isa<UndefValue>(Op0) || isa<UndefValue>(Op1))
-      return UndefValue::get(ReturnType);
+    // X + undef -> { -1, false } for undef = ~X.
+    // undef + X -> { -1, false } for undef = ~X.
+    if (isa<UndefValue>(Op0) || isa<UndefValue>(Op1)) {
+      StructType *ST = cast<StructType>(ReturnType);
+      Constant *Elems[] = {
+        Constant::getAllOnesValue(ST->getElementType(0)),
+        getFalse(ST->getElementType(1)),
+      };
+      return ConstantStruct::get(ST, Elems);
+    }
     break;
   case Intrinsic::umul_with_overflow:
   case Intrinsic::smul_with_overflow:
Index: llvm/test/Transforms/InstCombine/with_overflow.ll
===================================================================
--- llvm/test/Transforms/InstCombine/with_overflow.ll
+++ llvm/test/Transforms/InstCombine/with_overflow.ll
@@ -60,7 +60,8 @@
 
 define i8 @uaddtest4(i8 %A, i1* %overflowPtr) {
 ; CHECK-LABEL: @uaddtest4(
-; CHECK-NEXT:    ret i8 undef
+; CHECK-NEXT:    store i1 false, i1* [[OVERFLOWPTR:%.*]], align 1
+; CHECK-NEXT:    ret i8 -1
 ;
   %x = call { i8, i1 } @llvm.uadd.with.overflow.i8(i8 undef, i8 %A)
   %y = extractvalue { i8, i1 } %x, 0
Index: llvm/test/Transforms/InstSimplify/call.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/call.ll
+++ llvm/test/Transforms/InstSimplify/call.ll
@@ -29,7 +29,7 @@
 
 define {i8, i1} @test_uadd3(i8 %v) {
 ; CHECK-LABEL: @test_uadd3(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 -1, i1 false }
 ;
   %result = call {i8, i1} @llvm.uadd.with.overflow.i8(i8 %v, i8 undef)
   ret {i8, i1} %result
@@ -37,7 +37,7 @@
 
 define {i8, i1} @test_uadd4(i8 %v) {
 ; CHECK-LABEL: @test_uadd4(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 -1, i1 false }
 ;
   %result = call {i8, i1} @llvm.uadd.with.overflow.i8(i8 undef, i8 %v)
   ret {i8, i1} %result
@@ -63,7 +63,7 @@
 
 define {i8, i1} @test_sadd3(i8 %v) {
 ; CHECK-LABEL: @test_sadd3(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 -1, i1 false }
 ;
   %result = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 %v, i8 undef)
   ret {i8, i1} %result
@@ -71,7 +71,7 @@
 
 define {i8, i1} @test_sadd4(i8 %v) {
 ; CHECK-LABEL: @test_sadd4(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } { i8 -1, i1 false }
 ;
   %result = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 undef, i8 %v)
   ret {i8, i1} %result
@@ -87,7 +87,7 @@
 
 define {i8, i1} @test_usub2(i8 %V) {
 ; CHECK-LABEL: @test_usub2(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } zeroinitializer
 ;
   %x = call {i8, i1} @llvm.usub.with.overflow.i8(i8 %V, i8 undef)
   ret {i8, i1} %x
@@ -95,7 +95,7 @@
 
 define {i8, i1} @test_usub3(i8 %V) {
 ; CHECK-LABEL: @test_usub3(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } zeroinitializer
 ;
   %x = call {i8, i1} @llvm.usub.with.overflow.i8(i8 undef, i8 %V)
   ret {i8, i1} %x
@@ -111,7 +111,7 @@
 
 define {i8, i1} @test_ssub2(i8 %V) {
 ; CHECK-LABEL: @test_ssub2(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } zeroinitializer
 ;
   %x = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 %V, i8 undef)
   ret {i8, i1} %x
@@ -119,7 +119,7 @@
 
 define {i8, i1} @test_ssub3(i8 %V) {
 ; CHECK-LABEL: @test_ssub3(
-; CHECK-NEXT:    ret { i8, i1 } undef
+; CHECK-NEXT:    ret { i8, i1 } zeroinitializer
 ;
   %x = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 undef, i8 %V)
   ret {i8, i1} %x