Revert "Compute frontend/backend specific constants."

sdk/lib/_internal/compiler/implementation/compile_time_constants.dart

Index: sdk/lib/_internal/compiler/implementation/compile_time_constants.dart
diff --git a/sdk/lib/_internal/compiler/implementation/compile_time_constants.dart b/sdk/lib/_internal/compiler/implementation/compile_time_constants.dart
index cc0eac63aafbc4f065a6449c07f68e46dd66af0f..94523f092acdc2a38df11c8bef179891a973a8ec 100644
--- a/sdk/lib/_internal/compiler/implementation/compile_time_constants.dart
+++ b/sdk/lib/_internal/compiler/implementation/compile_time_constants.dart
@@ -4,77 +4,14 @@
 
 part of dart2js;
 
-/// A [ConstantEnvironment] provides access for constants compiled for variable
-/// initializers.
-abstract class ConstantEnvironment {
-  /// Returns the constant for the initializer of [element].
-  Constant getConstantForVariable(VariableElement element);
-}
-
-/// A class that can compile and provide constants for variables, nodes and
-/// metadata.
-abstract class ConstantCompiler extends ConstantEnvironment {
-  /// Compiles the compile-time constant for the initializer of [element], or
-  /// reports an error if the initializer is not a compile-time constant.
-  ///
-  /// Depending on implementation, the constant compiler might also compute
-  /// the compile-time constant for the backend interpretation of constants.
-  ///
-  /// The returned constant is always of the frontend interpretation.
-  Constant compileConstant(VariableElement element);
-
-  /// Computes the compile-time constant for the variable initializer,
-  /// if possible.
-  void compileVariable(VariableElement element);
-
-  /// Compiles the compile-time constant for [node], or reports an error if
-  /// [node] is not a compile-time constant.
-  ///
-  /// Depending on implementation, the constant compiler might also compute
-  /// the compile-time constant for the backend interpretation of constants.
-  ///
-  /// The returned constant is always of the frontend interpretation.
-  Constant compileNode(Node node, TreeElements elements);
-
-  /// Compiles the compile-time constant for the value [metadata], or reports an
-  /// error if the value is not a compile-time constant.
-  ///
-  /// Depending on implementation, the constant compiler might also compute
-  /// the compile-time constant for the backend interpretation of constants.
-  ///
-  /// The returned constant is always of the frontend interpretation.
-  Constant compileMetadata(MetadataAnnotation metadata,
-                           Node node, TreeElements elements);
-}
-
-/// A [BackendConstantEnvironment] provides access to constants needed for
-/// backend implementation.
-abstract class BackendConstantEnvironment extends ConstantEnvironment {
-  /// Returns the compile-time constant associated with [node].
-  ///
-  /// Depending on implementation, the constant might be stored in [elements].
-  Constant getConstantForNode(Node node, TreeElements elements);
-
-  /// Returns the compile-time constant value of [metadata].
-  Constant getConstantForMetadata(MetadataAnnotation metadata);
-}
-
-/// Interface for the task that compiles the constant environments for the
-/// frontend and backend interpretation of compile-time constants.
-abstract class ConstantCompilerTask extends CompilerTask
-    implements ConstantCompiler {
-  ConstantCompilerTask(Compiler compiler) : super(compiler);
-}
-
 /**
- * The [ConstantCompilerBase] is provides base implementation for compilation of
- * compile-time constants for both the Dart and JavaScript interpretation of
- * constants. It keeps track of compile-time constants for initializations of
- * global and static fields, and default values of optional parameters.
+ * The [ConstantHandler] keeps track of compile-time constants,
+ * initializations of global and static fields, and default values of
+ * optional parameters.
  */
-abstract class ConstantCompilerBase implements ConstantCompiler {
-  final Compiler compiler;
+class ConstantHandler extends CompilerTask {
   final ConstantSystem constantSystem;
+  final bool isMetadata;
 
   /**
    * Contains the initial value of fields. Must contain all static and global
@@ -83,40 +20,66 @@ abstract class ConstantCompilerBase implements ConstantCompiler {
    *
    * Invariant: The keys in this map are declarations.
    */
-  final Map<VariableElement, Constant> initialVariableValues =
-      new Map<VariableElement, Constant>();
+  final Map<VariableElement, Constant> initialVariableValues;
+
+  /** Set of all registered compiled constants. */
+  final Set<Constant> compiledConstants;
 
   /** The set of variable elements that are in the process of being computed. */
-  final Set<VariableElement> pendingVariables = new Set<VariableElement>();
+  final Set<VariableElement> pendingVariables;
+
+  /** Caches the statics where the initial value cannot be eagerly compiled. */
+  final Set<VariableElement> lazyStatics;
 
-  ConstantCompilerBase(this.compiler, this.constantSystem);
+  ConstantHandler(Compiler compiler, this.constantSystem,
+                  { bool this.isMetadata: false })
+      : initialVariableValues = new Map<VariableElement, dynamic>(),
+        compiledConstants = new Set<Constant>(),
+        pendingVariables = new Set<VariableElement>(),
+        lazyStatics = new Set<VariableElement>(),
+        super(compiler);
+
+  String get name => 'ConstantHandler';
+
+  void addCompileTimeConstantForEmission(Constant constant) {
+    compiledConstants.add(constant);
+  }
 
   Constant getConstantForVariable(VariableElement element) {
     return initialVariableValues[element.declaration];
   }
 
+  /**
+   * Returns a compile-time constant, or reports an error if the element is not
+   * a compile-time constant.
+   */
   Constant compileConstant(VariableElement element) {
     return compileVariable(element, isConst: true);
   }
 
+  /**
+   * Returns the a compile-time constant if the variable could be compiled
+   * eagerly. Otherwise returns `null`.
+   */
   Constant compileVariable(VariableElement element, {bool isConst: false}) {
-
-    if (initialVariableValues.containsKey(element.declaration)) {
-      Constant result = initialVariableValues[element.declaration];
-      return result;
-    }
-    Element currentElement = element;
-    if (element.isParameter() ||
-        element.isFieldParameter() ||
-        element.isVariable()) {
-      currentElement = element.enclosingElement;
-    }
-    return compiler.withCurrentElement(currentElement, () {
-      TreeElements definitions =
-          compiler.analyzeElement(currentElement.declaration);
-      Constant constant = compileVariableWithDefinitions(
-          element, definitions, isConst: isConst);
-      return constant;
+    return measure(() {
+      if (initialVariableValues.containsKey(element.declaration)) {
+        Constant result = initialVariableValues[element.declaration];
+        return result;
+      }
+      Element currentElement = element;
+      if (element.isParameter()
+          || element.isFieldParameter()
+          || element.isVariable()) {
+        currentElement = element.enclosingElement;
+      }
+      return compiler.withCurrentElement(currentElement, () {
+        TreeElements definitions =
+            compiler.analyzeElement(currentElement.declaration);
+        Constant constant = compileVariableWithDefinitions(
+            element, definitions, isConst: isConst);
+        return constant;
+      });
     });
   }
 
@@ -129,116 +92,149 @@ abstract class ConstantCompilerBase implements ConstantCompiler {
   Constant compileVariableWithDefinitions(VariableElement element,
                                           TreeElements definitions,
                                           {bool isConst: false}) {
-    Node node = element.parseNode(compiler);
-    if (pendingVariables.contains(element)) {
-      if (isConst) {
-        compiler.reportFatalError(
-            node, MessageKind.CYCLIC_COMPILE_TIME_CONSTANTS);
+    return measure(() {
+      if (!isConst && lazyStatics.contains(element)) return null;
+
+      Node node = element.parseNode(compiler);
+      if (pendingVariables.contains(element)) {
+        if (isConst) {
+          compiler.reportFatalError(
+              node, MessageKind.CYCLIC_COMPILE_TIME_CONSTANTS);
+        } else {
+          lazyStatics.add(element);
+          return null;
+        }
       }
-      return null;
-    }
-    pendingVariables.add(element);
+      pendingVariables.add(element);
 
-    Expression initializer = element.initializer;
-    Constant value;
-    if (initializer == null) {
-      // No initial value.
-      value = new NullConstant();
-    } else {
-      value = compileNodeWithDefinitions(
-          initializer, definitions, isConst: isConst);
-      if (compiler.enableTypeAssertions &&
-          value != null &&
-          element.isField()) {
-        DartType elementType = element.type;
-        if (elementType.kind == TypeKind.MALFORMED_TYPE && !value.isNull) {
-          if (isConst) {
-            ErroneousElement element = elementType.element;
-            compiler.reportFatalError(
-                node, element.messageKind, element.messageArguments);
-          } else {
-            // We need to throw an exception at runtime.
-            value = null;
-          }
-        } else {
-          DartType constantType = value.computeType(compiler);
-          if (!constantSystem.isSubtype(compiler,
-                                        constantType, elementType)) {
+      Expression initializer = element.initializer;
+      Constant value;
+      if (initializer == null) {
+        // No initial value.
+        value = new NullConstant();
+      } else {
+        value = compileNodeWithDefinitions(
+            initializer, definitions, isConst: isConst);
+        if (compiler.enableTypeAssertions &&
+            value != null &&
+            element.isField()) {
+          DartType elementType = element.type;
+          if (elementType.kind == TypeKind.MALFORMED_TYPE && !value.isNull) {
             if (isConst) {
+              ErroneousElement element = elementType.element;
               compiler.reportFatalError(
-                  node, MessageKind.NOT_ASSIGNABLE,
-                  {'fromType': constantType, 'toType': elementType});
+                  node, element.messageKind, element.messageArguments);
             } else {
-              // If the field cannot be lazily initialized, we will throw
-              // the exception at runtime.
+              // We need to throw an exception at runtime.
               value = null;
             }
+          } else {
+            DartType constantType = value.computeType(compiler);
+            if (!constantSystem.isSubtype(compiler,
+                                          constantType, elementType)) {
+              if (isConst) {
+                compiler.reportFatalError(
+                    node, MessageKind.NOT_ASSIGNABLE,
+                    {'fromType': constantType, 'toType': elementType});
+              } else {
+                // If the field cannot be lazily initialized, we will throw
+                // the exception at runtime.
+                value = null;
+              }
+            }
           }
         }
       }
-    }
-    if (value != null) {
-      initialVariableValues[element.declaration] = value;
-    } else {
-      assert(!isConst);
-    }
-    pendingVariables.remove(element);
-    return value;
+      if (value != null) {
+        initialVariableValues[element.declaration] = value;
+      } else {
+        assert(!isConst);
+        lazyStatics.add(element);
+      }
+      pendingVariables.remove(element);
+      return value;
+    });
   }
 
   Constant compileNodeWithDefinitions(Node node,
                                       TreeElements definitions,
-                                      {bool isConst: true}) {
-    assert(node != null);
-    CompileTimeConstantEvaluator evaluator = new CompileTimeConstantEvaluator(
-        this, definitions, compiler, isConst: isConst);
-    return evaluator.evaluate(node);
+                                      {bool isConst: false}) {
+    return measure(() {
+      assert(node != null);
+      Constant constant = definitions.getConstant(node);
+      if (constant != null) {
+        return constant;
+      }
+      CompileTimeConstantEvaluator evaluator = new CompileTimeConstantEvaluator(
+          this, definitions, compiler, isConst: isConst);
+      constant = evaluator.evaluate(node);
+      if (constant != null) {
+        definitions.setConstant(node, constant);
+      }
+      return constant;
+    });
   }
 
-  Constant compileNode(Node node, TreeElements elements) {
-    return compileNodeWithDefinitions(node, elements);
+  /**
+   * Returns an [Iterable] of static non final fields that need to be
+   * initialized. The fields list must be evaluated in order since they might
+   * depend on each other.
+   */
+  Iterable<VariableElement> getStaticNonFinalFieldsForEmission() {
+    return initialVariableValues.keys.where((element) {
+      return element.kind == ElementKind.FIELD
+          && !element.isInstanceMember()
+          && !element.modifiers.isFinal()
+          // The const fields are all either emitted elsewhere or inlined.
+          && !element.modifiers.isConst();
+    });
   }
 
-  Constant compileMetadata(MetadataAnnotation metadata,
-                           Node node,
-                           TreeElements elements) {
-    return compileNodeWithDefinitions(node, elements);
+  List<VariableElement> getLazilyInitializedFieldsForEmission() {
+    return new List<VariableElement>.from(lazyStatics);
   }
-}
 
-/// [ConstantCompiler] that uses the Dart semantics for the compile-time
-/// constant evaluation.
-class DartConstantCompiler extends ConstantCompilerBase {
-  DartConstantCompiler(Compiler compiler)
-      : super(compiler, const DartConstantSystem());
-
-  Constant getConstantForNode(Node node, TreeElements definitions) {
-    return definitions.getConstant(node);
-  }
+  /**
+   * Returns a list of constants topologically sorted so that dependencies
+   * appear before the dependent constant.  [preSortCompare] is a comparator
+   * function that gives the constants a consistent order prior to the
+   * topological sort which gives the constants an ordering that is less
+   * sensitive to perturbations in the source code.
+   */
+  List<Constant> getConstantsForEmission([preSortCompare]) {
+    // We must emit dependencies before their uses.
+    Set<Constant> seenConstants = new Set<Constant>();
+    List<Constant> result = new List<Constant>();
+
+    void addConstant(Constant constant) {
+      if (!seenConstants.contains(constant)) {
+        constant.getDependencies().forEach(addConstant);
+        assert(!seenConstants.contains(constant));
+        result.add(constant);
+        seenConstants.add(constant);
+      }
+    }
 
-  Constant getConstantForMetadata(MetadataAnnotation metadata) {
-    return metadata.value;
+    List<Constant> sorted = compiledConstants.toList();
+    if (preSortCompare != null) {
+      sorted.sort(preSortCompare);
+    }
+    sorted.forEach(addConstant);
+    return result;
   }
 
-  Constant compileNodeWithDefinitions(Node node,
-                                      TreeElements definitions,
-                                      {bool isConst: true}) {
-    Constant constant = definitions.getConstant(node);
-    if (constant != null) {
-      return constant;
+  Constant getInitialValueFor(VariableElement element) {
+    Constant initialValue = initialVariableValues[element.declaration];
+    if (initialValue == null) {
+      compiler.internalError(element, "No initial value for given element.");
     }
-    constant =
-        super.compileNodeWithDefinitions(node, definitions, isConst: isConst);
-    if (constant != null) {
-      definitions.setConstant(node, constant);
-    }
-    return constant;
+    return initialValue;
   }
 }
 
 class CompileTimeConstantEvaluator extends Visitor {
   bool isEvaluatingConstant;
-  final ConstantCompilerBase handler;
+  final ConstantHandler handler;
   final TreeElements elements;
   final Compiler compiler;
 
@@ -444,14 +440,6 @@ class CompileTimeConstantEvaluator extends Visitor {
     return false;
   }
 
-  Constant visitIdentifier(Identifier node) {
-    Element element = elements[node];
-    if (Elements.isClass(element) || Elements.isTypedef(element)) {
-      return makeTypeConstant(element);
-    }
-    return signalNotCompileTimeConstant(node);
-  }
-
   // TODO(floitsch): provide better error-messages.
   Constant visitSend(Send send) {
     Element element = elements[send];
@@ -489,6 +477,11 @@ class CompileTimeConstantEvaluator extends Visitor {
         Constant right = evaluate(send.argumentsNode.nodes.tail.head);
         Constant result = constantSystem.identity.fold(left, right);
         if (result != null) return result;
+      } else if (Elements.isClass(element) || Elements.isTypedef(element)) {
+        // The node itself is not a constant but we register the selector (the
+        // identifier that refers to the class/typedef) as a constant.
+        Constant typeConstant = makeTypeConstant(element);
+        elements.setConstant(send.selector, typeConstant);
       }
       return signalNotCompileTimeConstant(send);
     } else if (send.isPrefix) {
@@ -817,7 +810,7 @@ class ConstructorEvaluator extends CompileTimeConstantEvaluator {
    * Invariant: [constructor] must be an implementation element.
    */
   ConstructorEvaluator(FunctionElement constructor,
-                       ConstantCompiler handler,
+                       ConstantHandler handler,
                        Compiler compiler)
       : this.constructor = constructor,
         this.definitions = new Map<Element, Constant>(),
@@ -850,8 +843,6 @@ class ConstructorEvaluator extends CompileTimeConstantEvaluator {
       // TODO(ngeoffray): Handle type parameters.
       if (elementType.element.isTypeVariable()) return;
       if (!constantSystem.isSubtype(compiler, constantType, elementType)) {
-        // TODO(johnniwinther): Provide better [node] values that point to the
-        // origin of the constant and not (just) the assignment.
         compiler.reportFatalError(
             node, MessageKind.NOT_ASSIGNABLE,
             {'fromType': elementType, 'toType': constantType});