dart2js: Implement frequency based naming.

pkg/compiler/lib/src/js_emitter/metadata_collector.dart

Index: pkg/compiler/lib/src/js_emitter/metadata_collector.dart
diff --git a/pkg/compiler/lib/src/js_emitter/metadata_collector.dart b/pkg/compiler/lib/src/js_emitter/metadata_collector.dart
index 68ec03dcfc3492f195c7841654fd80f8ff3be139..826616d9fa264eace061eda35c8988e0888d140d 100644
--- a/pkg/compiler/lib/src/js_emitter/metadata_collector.dart
+++ b/pkg/compiler/lib/src/js_emitter/metadata_collector.dart
@@ -10,7 +10,7 @@ part of dart2js.js_emitter;
 /// ast for a program.
 /// [value] is the actual position, once they have been finalized.
 abstract class _MetadataEntry extends jsAst.DeferredNumber
-    implements Comparable {
+    implements Comparable, jsAst.ReferenceCountedAstNode {
   jsAst.Expression get entry;
   int get value;
   int get _rc;
@@ -18,7 +18,7 @@ abstract class _MetadataEntry extends jsAst.DeferredNumber
   // Mark this entry as seen. On the first time this is seen, the visitor
   // will be applied to the [entry] to also mark potential [_MetadataEntry]
   // instances in the [entry] as seen.
-  markSeen(jsAst.BaseVisitor visitor);
+  markSeen(jsAst.TokenCounter visitor);
 }
 
 class _BoundMetadataEntry extends _MetadataEntry {
@@ -107,7 +107,7 @@ class _MetadataList extends jsAst.DeferredExpression {
   int get precedenceLevel => js_precedence.PRIMARY;
 }
 
-class MetadataCollector implements TokenFinalizer {
+class MetadataCollector implements jsAst.TokenFinalizer {
   final Compiler _compiler;
   final Emitter _emitter;
 
@@ -232,7 +232,10 @@ class MetadataCollector implements TokenFinalizer {
   }
 
   _MetadataEntry _addGlobalMetadata(jsAst.Node node) {
-    String printed = jsAst.prettyPrint(node, _compiler).getText();
+    String nameToHashCode(jsAst.Name name) => "${name.hashCode}";

[sra1, 2015/07/01 04:11:09]

Q1. Are you guaranteeing somewhere that each unique name in the program has only
one instance of a jsAst.Name? That would make sense for refcounting.

Q2. What if the hashCodes are not unique?
At least document a TODO to investigate.
Maybe _NamerName should implement a hashString() method that returns a
structurally unique string for this purpose.

[herhut, 2015/07/02 08:54:51]

Yes. freshName (which hands out jsAst.Name) produces a fresh, unique name. The
Namer makes sure that consecutive calls with the same element or entity that
needs naming will result in the same name.

However, if the same name is constructed in different ways (like a literal
string gx and a getter with x) this does not hold. That is documented in the
namer and if that is violated, reference counting is the smallest issue.
True. I will add a TODO and implement unique keys in a follow-up.

+    String printed = jsAst.prettyPrint(node, _compiler,
+                                       renamerForNames: nameToHashCode)
+                          .getText();
     return _globalMetadataMap.putIfAbsent(printed, () {
       _BoundMetadataEntry result = new _BoundMetadataEntry(node);
       if (_compiler.hasIncrementalSupport) {
@@ -298,12 +301,6 @@ class MetadataCollector implements TokenFinalizer {
   }
 
   @override
-  void countTokensInAst(jsAst.Node ast) {
-    TokenCounter visitor = new TokenCounter();
-    visitor.countTokens(ast);
-  }
-
-  @override
   void finalizeTokens() {
     bool checkTokensInTypes(OutputUnit outputUnit, entries) {
       UnBoundDebugger debugger = new UnBoundDebugger(outputUnit);
@@ -316,7 +313,7 @@ class MetadataCollector implements TokenFinalizer {
       return true;
     }
     void countTokensInTypes(Iterable<_BoundMetadataEntry> entries) {
-      TokenCounter counter = new TokenCounter();
+      jsAst.TokenCounter counter = new jsAst.TokenCounter();
       entries.where((_BoundMetadataEntry e) => e._rc > 0)
              .map((_BoundMetadataEntry e) => e.entry)
              .forEach(counter.countTokens);
@@ -360,39 +357,6 @@ class MetadataCollector implements TokenFinalizer {
   }
 }
 
-/// Interface for ast nodes that encapsulate an ast that needs to be
-/// traversed when counting tokens.
-///
-/// TODO(herhut): Find a shared place once namer also uses tokens.
-abstract class AstContainer implements jsAst.Node {
-  jsAst.Node get ast;
-}
-
-abstract class TokenFinalizer {
-  void countTokensInAst(jsAst.Node ast);
-  void finalizeTokens();
-}
-
-class TokenCounter extends jsAst.BaseVisitor {
-  @override
-  visitNode(jsAst.Node node) {
-    if (node is AstContainer) {
-      node.ast.accept(this);
-    } else {
-      super.visitNode(node);
-    }
-  }
-
-  @override
-  visitDeferredNumber(jsAst.DeferredNumber token) {
-    if (token is _MetadataEntry) {
-      token.markSeen(this);
-    }
-  }
-
-  void countTokens(jsAst.Node node) => node.accept(this);
-}
-
 class UnBoundDebugger extends jsAst.BaseVisitor {
   OutputUnit outputUnit;
   bool _foundUnboundToken = false;