The MDString class stored a StringRef to the string which was already in a

StringMap. This was redundant and unnecessarily bloated the MDString class.

Because the MDString class is a "Value" and will never have a "name", and
because the Name field in the Value class is a pointer to a StringMap entry, we
repurpose the Name field for an MDString. It stores the StringMap entry in the
Name field, and uses the normal methods to get the string (name) back.

PR12474


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154429 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Metadata.h

@@ -39,28 +39,24 @@ class MDString : public Value {
   virtual void anchor();
   MDString(const MDString &);            // DO NOT IMPLEMENT
 
-  StringRef Str;
-  explicit MDString(LLVMContext &C, StringRef S);
-
+  explicit MDString(LLVMContext &C);
 public:
   static MDString *get(LLVMContext &Context, StringRef Str);
   static MDString *get(LLVMContext &Context, const char *Str) {
     return get(Context, Str ? StringRef(Str) : StringRef());
   }
 
-  StringRef getString() const { return Str; }
+  StringRef getString() const { return getName(); }
 
-  unsigned getLength() const { return (unsigned)Str.size(); }
+  unsigned getLength() const { return (unsigned)getName().size(); }
 
   typedef StringRef::iterator iterator;
   
   /// begin() - Pointer to the first byte of the string.
-  ///
-  iterator begin() const { return Str.begin(); }
+  iterator begin() const { return getName().begin(); }
 
   /// end() - Pointer to one byte past the end of the string.
-  ///
-  iterator end() const { return Str.end(); }
+  iterator end() const { return getName().end(); }
 
   /// Methods for support type inquiry through isa, cast, and dyn_cast:
   static inline bool classof(const MDString *) { return true; }

include/llvm/Value.h

@@ -107,9 +107,10 @@ public:
   /// All values hold a context through their type.
   LLVMContext &getContext() const;
 
-  // All values can potentially be named...
-  bool hasName() const { return Name != 0; }
+  // All values can potentially be named.
+  bool hasName() const { return Name != 0 && SubclassID != MDStringVal; }
   ValueName *getValueName() const { return Name; }
+  void setValueName(ValueName *VN) { Name = VN; }
   
   /// getName() - Return a constant reference to the value's name. This is cheap
   /// and guaranteed to return the same reference as long as the value is not

lib/VMCore/LLVMContextImpl.h

@@ -234,7 +234,7 @@ public:
                          DenseMapAPFloatKeyInfo> FPMapTy;
   FPMapTy FPConstants;
   
-  StringMap<MDString*> MDStringCache;
+  StringMap<Value*> MDStringCache;
   
   FoldingSet<MDNode> MDNodeSet;
   // MDNodes may be uniqued or not uniqued.  When they're not uniqued, they

lib/VMCore/Metadata.cpp

@@ -31,16 +31,17 @@ using namespace llvm;
 
 void MDString::anchor() { }
 
-MDString::MDString(LLVMContext &C, StringRef S)
-  : Value(Type::getMetadataTy(C), Value::MDStringVal), Str(S) {}
+MDString::MDString(LLVMContext &C)
+  : Value(Type::getMetadataTy(C), Value::MDStringVal) {}
 
 MDString *MDString::get(LLVMContext &Context, StringRef Str) {
   LLVMContextImpl *pImpl = Context.pImpl;
-  StringMapEntry<MDString *> &Entry =
+  StringMapEntry<Value*> &Entry =
     pImpl->MDStringCache.GetOrCreateValue(Str);
-  MDString *&S = Entry.getValue();
-  if (!S) S = new MDString(Context, Entry.getKey());
-  return S;
+  Value *&S = Entry.getValue();
+  if (!S) S = new MDString(Context);
+  S->setValueName(&Entry);
+  return cast<MDString>(S);
 }
 
 //===----------------------------------------------------------------------===//

lib/VMCore/Value.cpp

@@ -76,7 +76,7 @@ Value::~Value() {
 
   // If this value is named, destroy the name.  This should not be in a symtab
   // at this point.
-  if (Name)
+  if (Name && SubclassID != MDStringVal)
     Name->Destroy();
 
   // There should be no uses of this object anymore, remove it.
@@ -170,6 +170,9 @@ StringRef Value::getName() const {
 }
 
 void Value::setName(const Twine &NewName) {
+  assert(SubclassID != MDStringVal &&
+         "Cannot set the name of MDString with this method!");
+
   // Fast path for common IRBuilder case of setName("") when there is no name.
   if (NewName.isTriviallyEmpty() && !hasName())
     return;
@@ -228,6 +231,8 @@ void Value::setName(const Twine &NewName) {
 /// takeName - transfer the name from V to this value, setting V's name to
 /// empty.  It is an error to call V->takeName(V).
 void Value::takeName(Value *V) {
+  assert(SubclassID != MDStringVal && "Cannot take the name of an MDString!");
+
   ValueSymbolTable *ST = 0;
   // If this value has a name, drop it.
   if (hasName()) {