IR: Clarify ownership of ConstantDataSequentials, NFC

Change `ConstantDataSequential::Next` to a
`unique_ptr<ConstantDataSequential>` and update `CDSConstants` to a
`StringMap<unique_ptr<ConstantDataSequential>>`, making the ownership
more obvious.

Differential Revision: https://reviews.llvm.org/D90083

llvm/include/llvm/IR/Constants.h

@@ -592,14 +592,13 @@ class ConstantDataSequential : public ConstantData {
   /// the same value but different type.  For example, 0,0,0,1 could be a 4
   /// element array of i8, or a 1-element array of i32.  They'll both end up in
   /// the same StringMap bucket, linked up.
-  ConstantDataSequential *Next;
+  std::unique_ptr<ConstantDataSequential> Next;
 
   void destroyConstantImpl();
 
 protected:
   explicit ConstantDataSequential(Type *ty, ValueTy VT, const char *Data)
-      : ConstantData(ty, VT), DataElements(Data), Next(nullptr) {}
-  ~ConstantDataSequential() { delete Next; }
+      : ConstantData(ty, VT), DataElements(Data) {}
 
   static Constant *getImpl(StringRef Bytes, Type *Ty);
 

llvm/lib/IR/Constants.cpp

@@ -2783,56 +2783,55 @@ Constant *ConstantDataSequential::getImpl(StringRef Elements, Type *Ty) {
   // body but different types.  For example, 0,0,0,1 could be a 4 element array
   // of i8, or a 1-element array of i32.  They'll both end up in the same
   /// StringMap bucket, linked up by their Next pointers.  Walk the list.
-  ConstantDataSequential **Entry = &Slot.second;
-  for (ConstantDataSequential *Node = *Entry; Node;
-       Entry = &Node->Next, Node = *Entry)
+  std::unique_ptr<ConstantDataSequential> *Entry = &Slot.second;
+  for (ConstantDataSequential *Node = Entry->get(); Node;
+       Entry = &Node->Next, Node = Entry->get())
     if (Node->getType() == Ty)
       return Node;
 
   // Okay, we didn't get a hit.  Create a node of the right class, link it in,
   // and return it.
-  if (isa<ArrayType>(Ty))
-    return *Entry = new ConstantDataArray(Ty, Slot.first().data());
+  if (isa<ArrayType>(Ty)) {
+    Entry->reset(new ConstantDataArray(Ty, Slot.first().data()));
+    return Entry->get();
+  }
 
   assert(isa<VectorType>(Ty));
-  return *Entry = new ConstantDataVector(Ty, Slot.first().data());
+  Entry->reset(new ConstantDataVector(Ty, Slot.first().data()));
+  return Entry->get();
 }
 
 void ConstantDataSequential::destroyConstantImpl() {
   // Remove the constant from the StringMap.
-  StringMap<ConstantDataSequential*> &CDSConstants =
-    getType()->getContext().pImpl->CDSConstants;
+  StringMap<std::unique_ptr<ConstantDataSequential>> &CDSConstants =
+      getType()->getContext().pImpl->CDSConstants;
 
-  StringMap<ConstantDataSequential*>::iterator Slot =
-    CDSConstants.find(getRawDataValues());
+  auto Slot = CDSConstants.find(getRawDataValues());
 
   assert(Slot != CDSConstants.end() && "CDS not found in uniquing table");
 
-  ConstantDataSequential **Entry = &Slot->getValue();
+  std::unique_ptr<ConstantDataSequential> *Entry = &Slot->getValue();
 
   // Remove the entry from the hash table.
   if (!(*Entry)->Next) {
     // If there is only one value in the bucket (common case) it must be this
     // entry, and removing the entry should remove the bucket completely.
-    assert((*Entry) == this && "Hash mismatch in ConstantDataSequential");
+    assert(Entry->get() == this && "Hash mismatch in ConstantDataSequential");
     getContext().pImpl->CDSConstants.erase(Slot);
-  } else {
-    // Otherwise, there are multiple entries linked off the bucket, unlink the
-    // node we care about but keep the bucket around.
-    for (ConstantDataSequential *Node = *Entry; ;
-         Entry = &Node->Next, Node = *Entry) {
-      assert(Node && "Didn't find entry in its uniquing hash table!");
-      // If we found our entry, unlink it from the list and we're done.
-      if (Node == this) {
-        *Entry = Node->Next;
-        break;
-      }
-    }
+    return;
   }
 
-  // If we were part of a list, make sure that we don't delete the list that is
-  // still owned by the uniquing map.
-  Next = nullptr;
+  // Otherwise, there are multiple entries linked off the bucket, unlink the
+  // node we care about but keep the bucket around.
+  for (ConstantDataSequential *Node = Entry->get();;
+       Entry = &Node->Next, Node = Entry->get()) {
+    assert(Node && "Didn't find entry in its uniquing hash table!");
+    // If we found our entry, unlink it from the list and we're done.
+    if (Node == this) {
+      *Entry = std::move(Node->Next);
+      return;
+    }
+  }
 }
 
 /// getFP() constructors - Return a constant of array type with a float

llvm/lib/IR/LLVMContextImpl.cpp

@@ -99,9 +99,6 @@ LLVMContextImpl::~LLVMContextImpl() {
   UVConstants.clear();
   IntConstants.clear();
   FPConstants.clear();
-
-  for (auto &CDSConstant : CDSConstants)
-    delete CDSConstant.second;
   CDSConstants.clear();
 
   // Destroy attribute node lists.

llvm/lib/IR/LLVMContextImpl.h

@@ -1346,7 +1346,7 @@ public:
 
   DenseMap<Type *, std::unique_ptr<UndefValue>> UVConstants;
 
-  StringMap<ConstantDataSequential*> CDSConstants;
+  StringMap<std::unique_ptr<ConstantDataSequential>> CDSConstants;
 
   DenseMap<std::pair<const Function *, const BasicBlock *>, BlockAddress *>
     BlockAddresses;