[PATCH] D13946: Shrink DynTypedNode by one pointer from 40 to 32 bytes (on x86_64).

[Benjamin Kramer via cfe-commits]

bkramer created this revision.
bkramer added a reviewer: sbenza.
bkramer added a subscriber: cfe-commits.
Herald added a subscriber: klimek.

The MemoizationData cache was introduced to avoid a series of enum
compares at the cost of making DynTypedNode bigger. This change reverts
to using an enum compare but instead of building a chain of comparison
the enum values are reordered so the check can be performed with a
simple greater than. The alternative would be to steal a bit from the
enum but I think that's a more complex solution and not really needed
here.

I tried this on several large .cpp files with clang-tidy and didn't
notice any performance difference. The test change is due to matchers
being sorted by their node kind.

http://reviews.llvm.org/D13946

Files:
  include/clang/AST/ASTTypeTraits.h
  unittests/ASTMatchers/Dynamic/RegistryTest.cpp

Index: unittests/ASTMatchers/Dynamic/RegistryTest.cpp
===================================================================
--- unittests/ASTMatchers/Dynamic/RegistryTest.cpp
+++ unittests/ASTMatchers/Dynamic/RegistryTest.cpp
@@ -455,8 +455,8 @@
   // Polymorphic.
   EXPECT_TRUE(hasCompletion(
       Comps, "hasDescendant(",
-      "Matcher<NestedNameSpecifier|NestedNameSpecifierLoc|QualType|...> "
-      "hasDescendant(Matcher<CXXCtorInitializer|NestedNameSpecifier|"
+      "Matcher<TemplateArgument|NestedNameSpecifier|NestedNameSpecifierLoc|...>"
+      " hasDescendant(Matcher<TemplateArgument|NestedNameSpecifier|"
       "NestedNameSpecifierLoc|...>)"));
 
   CompVector WhileComps = getCompletions("whileStmt", 0);
Index: include/clang/AST/ASTTypeTraits.h
===================================================================
--- include/clang/AST/ASTTypeTraits.h
+++ include/clang/AST/ASTTypeTraits.h
@@ -106,18 +106,25 @@
     }
   };
 
+  /// Check if the given ASTNodeKind identifies a type that offers pointer
+  /// identity. This is useful for the fast path in DynTypedNode.
+  bool hasPointerIdentity() const {
+    return KindId > NKI_LastKindWithoutPointerIdentity;
+  }
+
 private:
   /// \brief Kind ids.
   ///
   /// Includes all possible base and derived kinds.
   enum NodeKindId {
     NKI_None,
-    NKI_CXXCtorInitializer,
     NKI_TemplateArgument,
-    NKI_NestedNameSpecifier,
     NKI_NestedNameSpecifierLoc,
     NKI_QualType,
     NKI_TypeLoc,
+    NKI_LastKindWithoutPointerIdentity = NKI_TypeLoc,
+    NKI_CXXCtorInitializer,
+    NKI_NestedNameSpecifier,
     NKI_Decl,
 #define DECL(DERIVED, BASE) NKI_##DERIVED##Decl,
 #include "clang/AST/DeclNodes.inc"
@@ -238,7 +245,11 @@
   /// Note that this is not supported by all AST nodes. For AST nodes
   /// that don't have a pointer-defined identity inside the AST, this
   /// method returns NULL.
-  const void *getMemoizationData() const { return MemoizationData; }
+  const void *getMemoizationData() const {
+    return NodeKind.hasPointerIdentity()
+               ? *reinterpret_cast<void *const *>(Storage.buffer)
+               : nullptr;
+  }
 
   /// \brief Prints the node to the given output stream.
   void print(llvm::raw_ostream &OS, const PrintingPolicy &PP) const;
@@ -296,7 +307,6 @@
     static DynTypedNode create(const BaseT &Node) {
       DynTypedNode Result;
       Result.NodeKind = ASTNodeKind::getFromNode(Node);
-      Result.MemoizationData = &Node;
       new (Result.Storage.buffer) const BaseT * (&Node);
       return Result;
     }
@@ -316,7 +326,6 @@
     static DynTypedNode create(const T &Node) {
       DynTypedNode Result;
       Result.NodeKind = ASTNodeKind::getFromNodeKind<T>();
-      Result.MemoizationData = &Node;
       new (Result.Storage.buffer) const T * (&Node);
       return Result;
     }
@@ -336,14 +345,12 @@
     static DynTypedNode create(const T &Node) {
       DynTypedNode Result;
       Result.NodeKind = ASTNodeKind::getFromNodeKind<T>();
-      Result.MemoizationData = nullptr;
       new (Result.Storage.buffer) T(Node);
       return Result;
     }
   };
 
   ASTNodeKind NodeKind;
-  const void *MemoizationData;
 
   /// \brief Stores the data of the node.
   ///


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