Revert "Compute frontend/backend specific constants."

sdk/lib/_internal/compiler/implementation/js_backend/constant_handler_javascript.dart

-// Copyright (c) 2014, 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.
-
-part of js_backend;
-
-/// [ConstantCompilerTask] for compilation of constants for the JavaScript
-/// backend.
-///
-/// Since this task needs to distinguish between frontend and backend constants
-/// the actual compilation of the constants is forwarded to a
-/// [DartConstantCompiler] for the frontend interpretation of the constants and
-/// to a [JavaScriptConstantCompiler] for the backend interpretation.
-class JavaScriptConstantTask extends ConstantCompilerTask {
-  DartConstantCompiler dartConstantCompiler;
-  JavaScriptConstantCompiler jsConstantCompiler;
-
-  JavaScriptConstantTask(Compiler compiler)
-      : this.dartConstantCompiler = new DartConstantCompiler(compiler),
-        this.jsConstantCompiler =
-            new JavaScriptConstantCompiler(compiler),
-        super(compiler);
-
-  String get name => 'ConstantHandler';
-
-  Constant getConstantForVariable(VariableElement element) {
-    return dartConstantCompiler.getConstantForVariable(element);
-  }
-
-  Constant compileConstant(VariableElement element) {
-    return measure(() {
-      Constant result = dartConstantCompiler.compileConstant(element);
-      jsConstantCompiler.compileConstant(element);
-      return result;
-    });
-  }
-
-  void compileVariable(VariableElement element) {
-    measure(() {
-      jsConstantCompiler.compileVariable(element);
-    });
-  }
-
-  Constant compileNode(Node node, TreeElements elements) {
-    return measure(() {
-      Constant result =
-          dartConstantCompiler.compileNode(node, elements);
-      jsConstantCompiler.compileNode(node, elements);
-      return result;
-    });
-  }
-
-  Constant compileMetadata(MetadataAnnotation metadata,
-                           Node node,
-                           TreeElements elements) {
-    return measure(() {
-      Constant constant =
-          dartConstantCompiler.compileMetadata(metadata, node, elements);
-      jsConstantCompiler.compileMetadata(metadata, node, elements);
-      return constant;
-    });
-  }
-}
-
-/**
- * The [JavaScriptConstantCompiler] is used to keep track of compile-time
- * constants, initializations of global and static fields, and default values of
- * optional parameters for the JavaScript interpretation of constants.
- */
-class JavaScriptConstantCompiler extends ConstantCompilerBase
-    implements BackendConstantEnvironment {
-
-  /** Set of all registered compiled constants. */
-  final Set<Constant> compiledConstants = new Set<Constant>();
-
-  // TODO(johnniwinther): Move this to the backend constant handler.
-  /** Caches the statics where the initial value cannot be eagerly compiled. */
-  final Set<VariableElement> lazyStatics = new Set<VariableElement>();
-
-  // Constants computed for constant expressions.
-  final Map<Node, Constant> nodeConstantMap = new Map<Node, Constant>();
-
-  // Constants computed for metadata.
-  final Map<MetadataAnnotation, Constant> metadataConstantMap =
-      new Map<MetadataAnnotation, Constant>();
-
-  JavaScriptConstantCompiler(Compiler compiler)
-      : super(compiler, JAVA_SCRIPT_CONSTANT_SYSTEM);
-
-  Constant compileVariableWithDefinitions(VariableElement element,
-                                          TreeElements definitions,
-                                          {bool isConst: false}) {
-    if (!isConst && lazyStatics.contains(element)) {
-      return null;
-    }
-    Constant value = super.compileVariableWithDefinitions(
-        element, definitions, isConst: isConst);
-    if (!isConst && value == null) {
-      lazyStatics.add(element);
-    }
-    return value;
-  }
-
-  void addCompileTimeConstantForEmission(Constant constant) {
-    compiledConstants.add(constant);
-  }
-
-  /**
-   * 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();
-    });
-  }
-
-  List<VariableElement> getLazilyInitializedFieldsForEmission() {
-    return new List<VariableElement>.from(lazyStatics);
-  }
-
-  /**
-   * 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);
-      }
-    }
-
-    List<Constant> sorted = compiledConstants.toList();
-    if (preSortCompare != null) {
-      sorted.sort(preSortCompare);
-    }
-    sorted.forEach(addConstant);
-    return result;
-  }
-
-  Constant getInitialValueFor(VariableElement element) {
-    Constant initialValue = initialVariableValues[element.declaration];
-    if (initialValue == null) {
-      compiler.internalError(element, "No initial value for given element.");
-    }
-    return initialValue;
-  }
-
-  Constant compileNode(Node node, TreeElements elements) {
-    return compileNodeWithDefinitions(node, elements);
-  }
-
-  Constant compileNodeWithDefinitions(Node node,
-                                      TreeElements definitions,
-                                      {bool isConst: true}) {
-    Constant constant = nodeConstantMap[node];
-    if (constant != null) {
-      return constant;
-    }
-    constant =
-        super.compileNodeWithDefinitions(node, definitions, isConst: isConst);
-    if (constant != null) {
-      nodeConstantMap[node] = constant;
-    }
-    return constant;
-  }
-
-  Constant getConstantForNode(Node node, TreeElements definitions) {
-    Constant constant = nodeConstantMap[node];
-    if (constant != null) {
-      return constant;
-    }
-    return definitions.getConstant(node);
-  }
-
-  Constant getConstantForMetadata(MetadataAnnotation metadata) {
-    return metadataConstantMap[metadata];
-  }
-
-  Constant compileMetadata(MetadataAnnotation metadata,
-                           Node node,
-                           TreeElements elements) {
-    Constant constant = super.compileMetadata(metadata, node, elements);
-    metadataConstantMap[metadata] = constant;
-    return constant;
-  }
-
-  Constant createTypeConstant(TypeDeclarationElement element) {
-    DartType elementType = element.rawType;
-    DartType constantType =
-        compiler.backend.typeImplementation.computeType(compiler);
-    return new TypeConstant(elementType, constantType);
-  }
-}