[AST] Store Decl* and Stmt* directly into the ParentMap.

These are by far the most common types to be parents in the AST so it makes
sense to optimize for them. Put them directly into the value of the map.
This currently saves 32 bytes per parent in the map and a pointer
indirection at the cost of some additional complexity in the code.

Sadly this means we cannot return an ArrayRef from getParents anymore, add
a proxy class that can own a single DynTypedNode and otherwise behaves
exactly the same as ArrayRef.

For example on a random large file (X86ISelLowering.cpp) this reduces the
size of the parent map by 24 MB.

Differential Revision: http://reviews.llvm.org/D13976

llvm-svn: 251008

clang/include/clang/AST/ASTContext.h

@@ -453,8 +453,47 @@ public:
 
   /// \brief Maps from a node to its parents.
   typedef llvm::DenseMap<const void *,
-                         llvm::PointerUnion<ast_type_traits::DynTypedNode *,
-                                            ParentVector *>> ParentMap;
+                         llvm::PointerUnion4<const Decl *, const Stmt *,
+                                             ast_type_traits::DynTypedNode *,
+                                             ParentVector *>> ParentMap;
+
+  /// Container for either a single DynTypedNode or for an ArrayRef to
+  /// DynTypedNode. For use with ParentMap.
+  class DynTypedNodeList {
+    typedef ast_type_traits::DynTypedNode DynTypedNode;
+    llvm::AlignedCharArrayUnion<ast_type_traits::DynTypedNode,
+                                ArrayRef<DynTypedNode>> Storage;
+    bool IsSingleNode;
+
+  public:
+    DynTypedNodeList(const DynTypedNode &N) : IsSingleNode(true) {
+      new (Storage.buffer) DynTypedNode(N);
+    }
+    DynTypedNodeList(ArrayRef<DynTypedNode> A) : IsSingleNode(false) {
+      new (Storage.buffer) ArrayRef<DynTypedNode>(A);
+    }
+
+    const ast_type_traits::DynTypedNode *begin() const {
+      if (!IsSingleNode)
+        return reinterpret_cast<const ArrayRef<DynTypedNode> *>(Storage.buffer)
+            ->begin();
+      return reinterpret_cast<const DynTypedNode *>(Storage.buffer);
+    }
+
+    const ast_type_traits::DynTypedNode *end() const {
+      if (!IsSingleNode)
+        return reinterpret_cast<const ArrayRef<DynTypedNode> *>(Storage.buffer)
+            ->end();
+      return reinterpret_cast<const DynTypedNode *>(Storage.buffer) + 1;
+    }
+
+    size_t size() const { return end() - begin(); }
+    bool empty() const { return begin() == end(); }
+    const DynTypedNode &operator[](size_t N) const {
+      assert(N < size() && "Out of bounds!");
+      return *(begin() + N);
+    }
+  };
 
   /// \brief Returns the parents of the given node.
   ///
@@ -480,13 +519,11 @@ public:
   ///
   /// 'NodeT' can be one of Decl, Stmt, Type, TypeLoc,
   /// NestedNameSpecifier or NestedNameSpecifierLoc.
-  template <typename NodeT>
-  ArrayRef<ast_type_traits::DynTypedNode> getParents(const NodeT &Node) {
+  template <typename NodeT> DynTypedNodeList getParents(const NodeT &Node) {
     return getParents(ast_type_traits::DynTypedNode::create(Node));
   }
 
-  ArrayRef<ast_type_traits::DynTypedNode>
-  getParents(const ast_type_traits::DynTypedNode &Node);
+  DynTypedNodeList getParents(const ast_type_traits::DynTypedNode &Node);
 
   const clang::PrintingPolicy &getPrintingPolicy() const {
     return PrintingPolicy;

clang/lib/AST/ASTContext.cpp

@@ -797,8 +797,7 @@ void ASTContext::ReleaseParentMapEntries() {
   for (const auto &Entry : *AllParents) {
     if (Entry.second.is<ast_type_traits::DynTypedNode *>()) {
       delete Entry.second.get<ast_type_traits::DynTypedNode *>();
-    } else {
-      assert(Entry.second.is<ParentVector *>());
+    } else if (Entry.second.is<ParentVector *>()) {
       delete Entry.second.get<ParentVector *>();
     }
   }
@@ -8673,6 +8672,15 @@ bool ASTContext::AtomicUsesUnsupportedLibcall(const AtomicExpr *E) const {
 
 namespace {
 
+ast_type_traits::DynTypedNode
+getSingleDynTypedNodeFromParentMap(ASTContext::ParentMap::mapped_type U) {
+  if (const auto *D = U.template dyn_cast<const Decl *>())
+    return ast_type_traits::DynTypedNode::create(*D);
+  if (const auto *S = U.template dyn_cast<const Stmt *>())
+    return ast_type_traits::DynTypedNode::create(*S);
+  return *U.template get<ast_type_traits::DynTypedNode *>();
+}
+
   /// \brief A \c RecursiveASTVisitor that builds a map from nodes to their
   /// parents as defined by the \c RecursiveASTVisitor.
   ///
@@ -8728,16 +8736,23 @@ namespace {
         // do not have pointer identity.
         auto &NodeOrVector = (*Parents)[Node];
         if (NodeOrVector.isNull()) {
-          NodeOrVector = new ast_type_traits::DynTypedNode(ParentStack.back());
+          if (const auto *D = ParentStack.back().get<Decl>())
+            NodeOrVector = D;
+          else if (const auto *S = ParentStack.back().get<Stmt>())
+            NodeOrVector = S;
+          else
+            NodeOrVector =
+                new ast_type_traits::DynTypedNode(ParentStack.back());
         } else {
-          if (NodeOrVector.template is<ast_type_traits::DynTypedNode *>()) {
-            auto *Node =
-                NodeOrVector.template get<ast_type_traits::DynTypedNode *>();
-            auto *Vector = new ASTContext::ParentVector(1, *Node);
+          if (!NodeOrVector.template is<ASTContext::ParentVector *>()) {
+            auto *Vector = new ASTContext::ParentVector(
+                1, getSingleDynTypedNodeFromParentMap(NodeOrVector));
             NodeOrVector = Vector;
-            delete Node;
+            if (auto *Node =
+                    NodeOrVector
+                        .template dyn_cast<ast_type_traits::DynTypedNode *>())
+              delete Node;
           }
-          assert(NodeOrVector.template is<ASTContext::ParentVector *>());
 
           auto *Vector =
               NodeOrVector.template get<ASTContext::ParentVector *>();
@@ -8774,7 +8789,7 @@ namespace {
 
 } // end namespace
 
-ArrayRef<ast_type_traits::DynTypedNode>
+ASTContext::DynTypedNodeList
 ASTContext::getParents(const ast_type_traits::DynTypedNode &Node) {
   assert(Node.getMemoizationData() &&
          "Invariant broken: only nodes that support memoization may be "
@@ -8787,12 +8802,12 @@ ASTContext::getParents(const ast_type_traits::DynTypedNode &Node) {
   }
   ParentMap::const_iterator I = AllParents->find(Node.getMemoizationData());
   if (I == AllParents->end()) {
-    return None;
+    return llvm::ArrayRef<ast_type_traits::DynTypedNode>();
   }
-  if (auto *N = I->second.dyn_cast<ast_type_traits::DynTypedNode *>()) {
-    return llvm::makeArrayRef(N, 1);
+  if (auto *V = I->second.dyn_cast<ParentVector *>()) {
+    return llvm::makeArrayRef(*V);
   }
-  return *I->second.get<ParentVector *>();
+  return getSingleDynTypedNodeFromParentMap(I->second);
 }
 
 bool