[clang][NFC] refactor GlobalMethodPool to encapsulate its map

This refactor changes the GlobalMethodPool to a class that contains
the DenseMap of methods. This is to allow for the addition of a
separate DenseSet in a follow-up diff that will handle method
de-duplication when inserting methods into the global method pool.

Changes:
  - the `GlobalMethods` pair becomes `GlobalMethodPool::Lists`
  - the `GlobalMethodPool` becomes a class containing the `DenseMap` of methods
  - pass through methods are added to maintain most of the existing code without changing `MethodPool` -> `MethodPool.Methods` everywhere

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D109898

clang/include/clang/Sema/Sema.h

@@ -1419,8 +1419,22 @@ class Sema final {
   const llvm::MapVector<FieldDecl *, DeleteLocs> &
   getMismatchingDeleteExpressions() const;
 
-  typedef std::pair<ObjCMethodList, ObjCMethodList> GlobalMethods;
-  typedef llvm::DenseMap<Selector, GlobalMethods> GlobalMethodPool;
+  class GlobalMethodPool {
+  public:
+    using Lists = std::pair<ObjCMethodList, ObjCMethodList>;
+    using iterator = llvm::DenseMap<Selector, Lists>::iterator;
+    iterator begin() { return Methods.begin(); }
+    iterator end() { return Methods.end(); }
+    iterator find(Selector Sel) { return Methods.find(Sel); }
+    std::pair<iterator, bool> insert(std::pair<Selector, Lists> &&Val) {
+      return Methods.insert(Val);
+    }
+    int count(Selector Sel) const { return Methods.count(Sel); }
+    bool empty() const { return Methods.empty(); }
+
+  private:
+    llvm::DenseMap<Selector, Lists> Methods;
+  };
 
   /// Method Pool - allows efficient lookup when typechecking messages to "id".
   /// We need to maintain a list, since selectors can have differing signatures

clang/lib/Sema/SemaDeclObjC.cpp

@@ -3427,8 +3427,10 @@ void Sema::AddMethodToGlobalPool(ObjCMethodDecl *Method, bool impl,
 
   GlobalMethodPool::iterator Pos = MethodPool.find(Method->getSelector());
   if (Pos == MethodPool.end())
-    Pos = MethodPool.insert(std::make_pair(Method->getSelector(),
-                                           GlobalMethods())).first;
+    Pos = MethodPool
+              .insert(std::make_pair(Method->getSelector(),
+                                     GlobalMethodPool::Lists()))
+              .first;
 
   Method->setDefined(impl);
 
@@ -3636,7 +3638,7 @@ ObjCMethodDecl *Sema::LookupImplementedMethodInGlobalPool(Selector Sel) {
   if (Pos == MethodPool.end())
     return nullptr;
 
-  GlobalMethods &Methods = Pos->second;
+  GlobalMethodPool::Lists &Methods = Pos->second;
   for (const ObjCMethodList *Method = &Methods.first; Method;
        Method = Method->getNext())
     if (Method->getMethod() &&

clang/lib/Serialization/ASTReader.cpp

@@ -8208,8 +8208,9 @@ void ASTReader::ReadMethodPool(Selector Sel) {
     return;
 
   Sema &S = *getSema();
-  Sema::GlobalMethodPool::iterator Pos
-    = S.MethodPool.insert(std::make_pair(Sel, Sema::GlobalMethods())).first;
+  Sema::GlobalMethodPool::iterator Pos =
+      S.MethodPool.insert(std::make_pair(Sel, Sema::GlobalMethodPool::Lists()))
+          .first;
 
   Pos->second.first.setBits(Visitor.getInstanceBits());
   Pos->second.first.setHasMoreThanOneDecl(Visitor.instanceHasMoreThanOneDecl());