Cache compile-time constants on the script object, sometimes.

runtime/vm/parser.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_PARSER_H_
 #define VM_PARSER_H_
 
 #include "include/dart_api.h"
 
 #include "platform/assert.h"
@@ skipping 21 matching lines @@
 class Parser;
 
 struct CatchParamDesc;
 class ClassDesc;
 struct MemberDesc;
 struct ParamList;
 struct QualIdent;
 class TopLevel;
 class RecursionChecker;
 
-// We cache computed compile-time constants in a map so we can look them
-// up when the same code gets compiled again. The map key is a pair
-// (script url, token position) which is encoded in an array with 2
-// elements:
+// We cache compile time constants during compilation.  This allows us
+// to look them up when the same code gets compiled again.  During
+// background compilation, we are not able to evaluate the constants
+// so this cache is necessary to support background compilation.
+//
+// There are two places a constant can be cached, depending on whether
+// the script is in the vm heap (snapshot) or not.
+//
+// When a script is in the vm heap, we are not able to cache the
+// constants on the script itself (it is read-only) so we cache them
+// in a per-isolate shared map in the object store.  In this case the
+// map key is a pair (array) with 2 elements:
+//
 // - key[0] contains the canonicalized url of the script.
 // - key[1] contains the token position of the constant in the script.
+//
+// The VMConstantsMap type is used to implement this per-isolate map.
+//
+// When a script is not in the vm heap, we cache the constants with
+// the script itself.  This is helpful during isolate reloading, as it
+// allows us to reference the compile time constants associated with a
+// particular version of a script.  In this case the map key is simply
+// the TokenPosition where the constant is defined.
+//
+// The ConstantsMap type is used to implement this per-script map.
 
-// ConstantPosKey allows us to look up a constant in the map without
-// allocating a key pair (array).
-struct ConstantPosKey : ValueObject {
-  ConstantPosKey(const String& url, TokenPosition pos)
+// The key for the per-isolate compile time constants map.  By using a
+// ValueObject we are able to look up a constant without allocating a
+// key pair (array).
+// The per-script compile-time constants map.
+struct UrlAndPosKey : ValueObject {
+  UrlAndPosKey(const String& url, TokenPosition pos)
       : script_url(url), token_pos(pos) { }
   const String& script_url;
   TokenPosition token_pos;
 };
 
-
-class ConstMapKeyEqualsTraits {
+// The per-isolate compile-time constants map.
+class VMConstMapKeyEqualsTraits {
  public:
-  static const char* Name() { return "ConstMapKeyEqualsTraits"; }
+  static const char* Name() { return "VMConstMapKeyEqualsTraits"; }
   static bool ReportStats() { return false; }
 
   static bool IsMatch(const Object& a, const Object& b) {
     const Array& key1 = Array::Cast(a);
     const Array& key2 = Array::Cast(b);
     // Compare raw strings of script url symbol and raw smi of token positon.
     return (key1.At(0) == key2.At(0)) && (key1.At(1) == key2.At(1));
   }
-  static bool IsMatch(const ConstantPosKey& key1, const Object& b) {
+  static bool IsMatch(const UrlAndPosKey& key1, const Object& b) {
     const Array& key2 = Array::Cast(b);
     // Compare raw strings of script url symbol and token positon.
     return (key1.script_url.raw() == key2.At(0))
         && (key1.token_pos.value() == Smi::Value(Smi::RawCast(key2.At(1))));
   }
   static uword Hash(const Object& obj) {
     const Array& key = Array::Cast(obj);
     intptr_t url_hash = String::HashRawSymbol(String::RawCast(key.At(0)));
     intptr_t pos = Smi::Value(Smi::RawCast(key.At(1)));
     return HashValue(url_hash, pos);
   }
-  static uword Hash(const ConstantPosKey& key) {
+  static uword Hash(const UrlAndPosKey& key) {
     return HashValue(String::HashRawSymbol(key.script_url.raw()),
                      key.token_pos.value());
   }
-  // Used by CachConstantValue if a new constant is added to the map.
-  static RawObject* NewKey(const ConstantPosKey& key) {
+  // Used by CacheConstantValue if a new constant is added to the map.
+  static RawObject* NewKey(const UrlAndPosKey& key) {
     const Array& key_obj = Array::Handle(Array::New(2));
     key_obj.SetAt(0, key.script_url);
     key_obj.SetAt(1, Smi::Handle(Smi::New(key.token_pos.value())));
     return key_obj.raw();;
   }
 
  private:
   static uword HashValue(intptr_t url_hash, intptr_t pos) {
     return url_hash * pos % (Smi::kMaxValue - 13);
   }
 };
+typedef UnorderedHashMap<VMConstMapKeyEqualsTraits> VMConstantsMap;
+
+class ConstMapKeyEqualsTraits {
+ public:
+  static const char* Name() { return "ConstMapKeyEqualsTraits"; }
+  static bool ReportStats() { return false; }
+
+  static bool IsMatch(const Object& a, const Object& b) {
+    const Smi& key1 = Smi::Cast(a);
+    const Smi& key2 = Smi::Cast(b);
+    return (key1.Value() == key2.Value());
+  }
+  static bool IsMatch(const TokenPosition& key1, const Object& b) {
+    const Smi& key2 = Smi::Cast(b);
+    return (key1.value() == key2.Value());
+  }
+  static uword Hash(const Object& obj) {
+    const Smi& key = Smi::Cast(obj);
+    return HashValue(key.Value());
+  }
+  static uword Hash(const TokenPosition& key) {
+    return HashValue(key.value());
+  }
+  // Used by CacheConstantValue if a new constant is added to the map.
+  static RawObject* NewKey(const TokenPosition& key) {
+    return Smi::New(key.value());
+  }
+
+ private:
+  static uword HashValue(intptr_t pos) {
+    return pos % (Smi::kMaxValue - 13);
+  }
+};
 typedef UnorderedHashMap<ConstMapKeyEqualsTraits> ConstantsMap;
 
 // The class ParsedFunction holds the result of parsing a function.
 class ParsedFunction : public ZoneAllocated {
  public:
   ParsedFunction(Thread* thread, const Function& function)
       : thread_(thread),
         function_(function),
         code_(Code::Handle(zone(), function.unoptimized_code())),
         node_sequence_(NULL),
@@ skipping 162 matching lines @@
 
   // Parse and evaluate the metadata expressions at token_pos in the
   // class namespace of class cls (which can be the implicit toplevel
   // class if the metadata is at the top-level).
   static RawObject* ParseMetadata(const Field& meta_data);
 
   // Build a function containing the initializer expression of the
   // given static field.
   static ParsedFunction* ParseStaticFieldInitializer(const Field& field);
 
-  static void InsertCachedConstantValue(const String& url,
+  static void InsertCachedConstantValue(const Script& script,
                                         TokenPosition token_pos,
                                         const Instance& value);
 
   // Parse a function to retrieve parameter information that is not retained in
   // the dart::Function object. Returns either an error if the parse fails
   // (which could be the case for local functions), or a flat array of entries
   // for each parameter. Each parameter entry contains:
   // * a Dart bool indicating whether the parameter was declared final
   // * its default value (or null if none was declared)
   // * an array of metadata (or null if no metadata was declared).
@@ skipping 692 matching lines @@
 
   intptr_t recursion_counter_;
   friend class RecursionChecker;
 
   DISALLOW_COPY_AND_ASSIGN(Parser);
 };
 
 }  // namespace dart
 
 #endif  // VM_PARSER_H_