First step towards adding a parent map to the ASTContext.

This does not yet implement the LimitNode approach discussed.

The impact of this is an O(n) in the number of nodes in the AST
reduction of complexity for certain kinds of matchers (as otherwise the
parent map gets recreated for every new MatchFinder).

See FIXMEs in the comments for the direction of future work.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176251 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 128 insertions, 1 deletions

diff --git a/include/clang/AST/ASTContext.h b/include/clang/AST/ASTContext.h
index 7c02699ee4..d12d0545c5 100644
--- a/include/clang/AST/ASTContext.h
+++ b/include/clang/AST/ASTContext.h
@@ -15,6 +15,7 @@
 #ifndef LLVM_CLANG_AST_ASTCONTEXT_H
 #define LLVM_CLANG_AST_ASTCONTEXT_H
 
+#include "clang/AST/ASTTypeTraits.h"
 #include "clang/AST/CanonicalType.h"
 #include "clang/AST/CommentCommandTraits.h"
 #include "clang/AST/Decl.h"
@@ -22,6 +23,7 @@
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/PrettyPrinter.h"
 #include "clang/AST/RawCommentList.h"
+#include "clang/AST/RecursiveASTVisitor.h"
 #include "clang/AST/TemplateName.h"
 #include "clang/AST/Type.h"
 #include "clang/Basic/AddressSpaces.h"
@@ -382,6 +384,58 @@ public:
   OwningPtr<ExternalASTSource> ExternalSource;
   ASTMutationListener *Listener;
 
+  /// \brief Contains parents of a node.
+  typedef llvm::SmallVector<ast_type_traits::DynTypedNode, 1> ParentVector;
+
+  /// \brief Maps from a node to its parents.
+  typedef llvm::DenseMap<const void *, ParentVector> ParentMap;
+
+  /// \brief Returns the parents of the given node.
+  ///
+  /// Note that this will lazily compute the parents of all nodes
+  /// and store them for later retrieval. Thus, the first call is O(n)
+  /// in the number of AST nodes.
+  ///
+  /// Caveats and FIXMEs:
+  /// Calculating the parent map over all AST nodes will need to load the
+  /// full AST. This can be undesirable in the case where the full AST is
+  /// expensive to create (for example, when using precompiled header
+  /// preambles). Thus, there are good opportunities for optimization here.
+  /// One idea is to walk the given node downwards, looking for references
+  /// to declaration contexts - once a declaration context is found, compute
+  /// the parent map for the declaration context; if that can satisfy the
+  /// request, loading the whole AST can be avoided. Note that this is made
+  /// more complex by statements in templates having multiple parents - those
+  /// problems can be solved by building closure over the templated parts of
+  /// the AST, which also avoids touching large parts of the AST.
+  /// Additionally, we will want to add an interface to already give a hint
+  /// where to search for the parents, for example when looking at a statement
+  /// inside a certain function.
+  ///
+  /// 'NodeT' can be one of Decl, Stmt, Type, TypeLoc,
+  /// NestedNameSpecifier or NestedNameSpecifierLoc.
+  template <typename NodeT>
+  ParentVector getParents(const NodeT &Node) {
+    return getParents(ast_type_traits::DynTypedNode::create(Node));
+  }
+
+  ParentVector getParents(const ast_type_traits::DynTypedNode &Node) {
+    assert(Node.getMemoizationData() &&
+           "Invariant broken: only nodes that support memoization may be "
+           "used in the parent map.");
+    if (!AllParents) {
+      // We always need to run over the whole translation unit, as
+      // hasAncestor can escape any subtree.
+      AllParents.reset(
+          ParentMapASTVisitor::buildMap(*getTranslationUnitDecl()));
+    }
+    ParentMap::const_iterator I = AllParents->find(Node.getMemoizationData());
+    if (I == AllParents->end()) {
+      return ParentVector();
+    }
+    return I->second;
+  }
+
   const clang::PrintingPolicy &getPrintingPolicy() const {
     return PrintingPolicy;
   }
@@ -2136,8 +2190,81 @@ private:
   friend class DeclContext;
   friend class DeclarationNameTable;
   void ReleaseDeclContextMaps();
+
+  /// \brief A \c RecursiveASTVisitor that builds a map from nodes to their
+  /// parents as defined by the \c RecursiveASTVisitor.
+  ///
+  /// Note that the relationship described here is purely in terms of AST
+  /// traversal - there are other relationships (for example declaration context)
+  /// in the AST that are better modeled by special matchers.
+  ///
+  /// FIXME: Currently only builds up the map using \c Stmt and \c Decl nodes.
+  class ParentMapASTVisitor : public RecursiveASTVisitor<ParentMapASTVisitor> {
+  public:
+    /// \brief Builds and returns the translation unit's parent map.
+    ///
+    ///  The caller takes ownership of the returned \c ParentMap.
+    static ParentMap *buildMap(TranslationUnitDecl &TU) {
+      ParentMapASTVisitor Visitor(new ParentMap);
+      Visitor.TraverseDecl(&TU);
+      return Visitor.Parents;
+    }
+
+  private:
+    typedef RecursiveASTVisitor<ParentMapASTVisitor> VisitorBase;
+
+    ParentMapASTVisitor(ParentMap *Parents) : Parents(Parents) {
+    }
+
+    bool shouldVisitTemplateInstantiations() const {
+      return true;
+    }
+    bool shouldVisitImplicitCode() const {
+      return true;
+    }
+    // Disables data recursion. We intercept Traverse* methods in the RAV, which
+    // are not triggered during data recursion.
+    bool shouldUseDataRecursionFor(clang::Stmt *S) const {
+      return false;
+    }
+
+    template <typename T>
+    bool TraverseNode(T *Node, bool(VisitorBase:: *traverse) (T *)) {
+      if (Node == NULL)
+        return true;
+      if (ParentStack.size() > 0)
+        // FIXME: Currently we add the same parent multiple times, for example
+        // when we visit all subexpressions of template instantiations; this is
+        // suboptimal, bug benign: the only way to visit those is with
+        // hasAncestor / hasParent, and those do not create new matches.
+        // The plan is to enable DynTypedNode to be storable in a map or hash
+        // map. The main problem there is to implement hash functions /
+        // comparison operators for all types that DynTypedNode supports that
+        // do not have pointer identity.
+        (*Parents)[Node].push_back(ParentStack.back());
+      ParentStack.push_back(ast_type_traits::DynTypedNode::create(*Node));
+      bool Result = (this ->* traverse) (Node);
+      ParentStack.pop_back();
+      return Result;
+    }
+
+    bool TraverseDecl(Decl *DeclNode) {
+      return TraverseNode(DeclNode, &VisitorBase::TraverseDecl);
+    }
+
+    bool TraverseStmt(Stmt *StmtNode) {
+      return TraverseNode(StmtNode, &VisitorBase::TraverseStmt);
+    }
+
+    ParentMap *Parents;
+    llvm::SmallVector<ast_type_traits::DynTypedNode, 16> ParentStack;
+
+    friend class RecursiveASTVisitor<ParentMapASTVisitor>;
+  };
+
+  llvm::OwningPtr<ParentMap> AllParents;
 };
-  
+
 /// \brief Utility function for constructing a nullary selector.
 static inline Selector GetNullarySelector(StringRef name, ASTContext& Ctx) {
   IdentifierInfo* II = &Ctx.Idents.get(name);