IR: Rewrite uniquing and creation of MDString

Stop using `Value::getName()` to get the string behind an `MDString`.
Switch to `StringMapEntry<MDString>` so that we can find the string by
its coallocation.

This is part of PR21532.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221960 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/Metadata.h

@@ -57,14 +57,15 @@ public:
 ///
 /// TODO: Inherit from Metadata.
 class MDString : public Value {
+  friend class StringMapEntry<MDString>;
+
   virtual void anchor();
   MDString(const MDString &) LLVM_DELETED_FUNCTION;
 
   explicit MDString(LLVMContext &C);
 
-private:
   /// \brief Shadow Value::getName() to prevent its use.
-  StringRef getName() const { return Value::getName(); }
+  StringRef getName() const LLVM_DELETED_FUNCTION;
 
 public:
   static MDString *get(LLVMContext &Context, StringRef Str);
@@ -72,17 +73,17 @@ public:
     return get(Context, Str ? StringRef(Str) : StringRef());
   }
 
-  StringRef getString() const { return getName(); }
+  StringRef getString() const;
 
-  unsigned getLength() const { return (unsigned)getName().size(); }
+  unsigned getLength() const { return (unsigned)getString().size(); }
 
   typedef StringRef::iterator iterator;
 
   /// \brief Pointer to the first byte of the string.
-  iterator begin() const { return getName().begin(); }
+  iterator begin() const { return getString().begin(); }
 
   /// \brief Pointer to one byte past the end of the string.
-  iterator end() const { return getName().end(); }
+  iterator end() const { return getString().end(); }
 
   /// \brief Methods for support type inquiry through isa, cast, and dyn_cast.
   static bool classof(const Value *V) {

lib/IR/LLVMContextImpl.cpp

@@ -135,7 +135,7 @@ LLVMContextImpl::~LLVMContextImpl() {
          "Destroying all MDNodes didn't empty the Context's sets.");
 
   // Destroy MDStrings.
-  DeleteContainerSeconds(MDStringCache);
+  MDStringCache.clear();
 }
 
 // ConstantsContext anchors

lib/IR/LLVMContextImpl.h

@@ -261,7 +261,7 @@ public:
   FoldingSet<AttributeSetImpl> AttrsLists;
   FoldingSet<AttributeSetNode> AttrsSetNodes;
 
-  StringMap<Value*> MDStringCache;
+  StringMap<MDString> MDStringCache;
 
   FoldingSet<MDNode> MDNodeSet;
 

lib/IR/Metadata.cpp

@@ -37,13 +37,21 @@ MDString::MDString(LLVMContext &C)
   : Value(Type::getMetadataTy(C), Value::MDStringVal) {}
 
 MDString *MDString::get(LLVMContext &Context, StringRef Str) {
-  LLVMContextImpl *pImpl = Context.pImpl;
+  auto &Store = Context.pImpl->MDStringCache;
-  StringMapEntry<Value*> &Entry =
+  auto I = Store.find(Str);
-    pImpl->MDStringCache.GetOrCreateValue(Str);
+  if (I != Store.end())
-  Value *&S = Entry.getValue();
+    return &I->second;
-  if (!S) S = new MDString(Context);
+
-  S->setValueName(&Entry);
+  auto *Entry =
-  return cast<MDString>(S);
+      StringMapEntry<MDString>::Create(Str, Store.getAllocator(), Context);
+  bool WasInserted = Store.insert(Entry);
+  (void)WasInserted;
+  assert(WasInserted && "Expected entry to be inserted");
+  return &Entry->second;
+}
+
+StringRef MDString::getString() const {
+  return StringMapEntry<MDString>::GetStringMapEntryFromValue(*this).first();
 }
 
 //===----------------------------------------------------------------------===//