[Function] Properly remove use when clearing personality

[loladiro]

Summary

We need to actually remove the use of the personality function,
otherwise we can run into trouble if we want to e.g. delete
the personality function because ther's no way to get rid of
its uses. Do this by resetting to ConstantPointerNull value
that the operands are set to when first allocated.

[• rafael]

Lgtm

[vsk]

Thanks for the test, lgtm also.

lib/IR/Function.cpp

 }
 
 Constant *Function::getPersonalityFn() const {
   assert(hasPersonalityFn() && getNumOperands());
   return cast<Constant>(Op<0>());
 }
 
 void Function::setPersonalityFn(Constant *Fn) {
-  if (Fn)
-    setHungoffOperand<0>(Fn);
   setValueSubclassDataBit(3, Fn != nullptr);
 }
 
 Constant *Function::getPrefixData() const {
   assert(hasPrefixData() && getNumOperands());
   return cast<Constant>(Op<1>());
 }
 
 void Function::setPrefixData(Constant *PrefixData) {
-  if (PrefixData)
-    setHungoffOperand<1>(PrefixData);
   setValueSubclassDataBit(1, PrefixData != nullptr);
 }
 
 Constant *Function::getPrologueData() const {
   assert(hasPrologueData() && getNumOperands());
   return cast<Constant>(Op<2>());
 }
 
 void Function::setPrologueData(Constant *PrologueData) {
-  if (PrologueData)
-    setHungoffOperand<2>(PrologueData);
   setValueSubclassDataBit(2, PrologueData != nullptr);
 }
 
 void Function::allocHungoffUselist() {
   // If we've already allocated a uselist, stop here.
   if (getNumOperands())
     return;
 
   allocHungoffUses(3, /*IsPhi=*/ false);
   setNumHungOffUseOperands(3);
 
   // Initialize the uselist with placeholder operands to allow traversal.
   auto *CPN = ConstantPointerNull::get(Type::getInt1PtrTy(getContext(), 0));
   Op<0>().set(CPN);
   Op<1>().set(CPN);
   Op<2>().set(CPN);
 }
 
 template <int Idx>
 void Function::setHungoffOperand(Constant *C) {
-  assert(C && "Cannot set hungoff operand to nullptr");
+  if (C) {
     allocHungoffUselist();
     Op<Idx>().set(C);
+  } else if (getNumOperands()) {
+    Op<Idx>().set(
+        ConstantPointerNull::get(Type::getInt1PtrTy(getContext(), 0)));
+  }
 }
 
 void Function::setValueSubclassDataBit(unsigned Bit, bool On) {
   assert(Bit < 16 && "SubclassData contains only 16 bits");
   if (On)
     setValueSubclassData(getSubclassDataFromValue() | (1 << Bit));
   else
     setValueSubclassData(getSubclassDataFromValue() & ~(1 << Bit));

unittests/IR/UserTest.cpp

TEST(UserTest, ValueOpIteration) {
   I += 3;
   EXPECT_EQ(std::next(P.value_op_begin(), 3), I);
   EXPECT_EQ(P.getOperand(3), *I);
   I++;
   EXPECT_EQ(P.getOperand(6), I[2]);
   EXPECT_EQ(P.value_op_end(), (I - 2) + 8);
 }
 
+TEST(UserTest, PersonalityUser) {
+  Module M("", getGlobalContext());
+  FunctionType *RetVoidTy =
+      FunctionType::get(Type::getVoidTy(getGlobalContext()), false);
+  Function *PersonalityF = Function::Create(
+      RetVoidTy, GlobalValue::ExternalLinkage, "PersonalityFn", &M);
+  Function *TestF =
+      Function::Create(RetVoidTy, GlobalValue::ExternalLinkage, "TestFn", &M);
+
+  // Set up the personality function
+  TestF->setPersonalityFn(PersonalityF);
+  auto PersonalityUsers = PersonalityF->user_begin();
+
+  // One user and that user is the Test function
+  EXPECT_EQ(*PersonalityUsers, TestF);
+  EXPECT_EQ(++PersonalityUsers, PersonalityF->user_end());
+
+  // Reset the personality function
+  TestF->setPersonalityFn(nullptr);
+
+  // No users should remain
+  EXPECT_TRUE(TestF->user_empty());
+}
+
 } // end anonymous namespace