Build new IR for functions returning a constant

sdk/lib/_internal/compiler/implementation/ir/ir_builder.dart

+// Copyright (c) 2013, 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.
+
+library ir_builder;
+
+import 'ir_nodes.dart';
+import '../elements/elements.dart';
+import '../dart2jslib.dart';
+import '../source_file.dart';
+import '../tree/tree.dart';
+import '../scanner/scannerlib.dart' show Token;
+import '../js_backend/js_backend.dart' show JavaScriptBackend;
+
+/**
+ * This task iterates through all resolved elements and builds [IrNode]s. The
+ * nodes are stored in the [nodes] map and accessible through [Element.irNode]
+ * and [Element.hasIrNode].
+ *
+ * The functionality of the IrNodes is added gradually, therefore elements might
+ * have an IR or not, depending on the language features that are used. For
+ * elements that do have an IR, the tree [Node]s and the [Token]s are not used
+ * in the rest of the compilation. This is ensured by setting the element's
+ * cached tree to [:null:] and also breaking the token stream to crash future
+ * attempts to parse.
+ *
+ * The type inferrer works on either IR nodes or tree nodes. The IR nodes are
+ * then translated into the SSA form for optimizations and code generation.
+ * Long-term, once the IR supports the full language, the backend can be
+ * re-implemented to work directly on the IR.
+ */
+class IrBuilderTask extends CompilerTask {
+  final Map<Element, IrNode> nodes = new Map<Element, IrNode>();
+
+  IrBuilderTask(Compiler compiler) : super(compiler);
+
+  String get name => 'IR builder';
+
+  void buildNodes() {
+    if (!irEnabled()) return;
+    measure(() {
+      Map<Element, TreeElements> resolved =
+          compiler.enqueuer.resolution.resolvedElements;
+      resolved.forEach((Element element, TreeElements elementsMapping) {
+        if (canBuild(element)) {
+          element = element.implementation;
+
+          SourceFile sourceFile = elementSourceFile(element);
+          IrNodeBuilderVisitor visitor =
+              new IrNodeBuilderVisitor(elementsMapping, compiler, sourceFile);
+          IrNode irNode;
+          ElementKind kind = element.kind;
+          if (kind == ElementKind.GENERATIVE_CONSTRUCTOR) {
+            // TODO(lry): build ir for constructors.
+          } else if (kind == ElementKind.GENERATIVE_CONSTRUCTOR_BODY ||
+              kind == ElementKind.FUNCTION ||
+              kind == ElementKind.GETTER ||
+              kind == ElementKind.SETTER) {
+            irNode = visitor.buildMethod(element);
+          } else if (kind == ElementKind.FIELD) {
+            // TODO(lry): build ir for lazy initializers of static fields.
+          } else {
+            compiler.internalErrorOnElement(element,
+                'unexpected element kind $kind');
+          }
+
+          if (irNode != null) {
+            nodes[element] = irNode;
+            unlinkTreeAndToken(element);
+          }
+        }
+      });
+    });
+  }
+
+  bool irEnabled() {
+    // TODO(lry): support checked-mode checks.
+    if (compiler.enableTypeAssertions) return false;
+    if (compiler.backend is !JavaScriptBackend) return false;
+    return true;
+  }
+
+  bool canBuild(Element element) {
+    // TODO(lry): support lazy initializers.
+    FunctionElement function = element.asFunctionElement();
+    if (function == null) return false;
+
+    // TODO(lry): support functions with parameters.
+    FunctionSignature signature = function.computeSignature(compiler);
+    if (signature.parameterCount > 0) return false;
+
+    // TODO(lry): support intercepted methods. Then the dependency on
+    // JavaScriptBackend will go away.
+    JavaScriptBackend backend = compiler.backend;
+    if (backend.isInterceptedMethod(element)) return false;
+
+    return true;
+  }
+
+  void unlinkTreeAndToken(element) {
+    element.beginToken.next = null;
+    element.cachedNode = null;
+  }
+
+  SourceFile elementSourceFile(Element element) {
+    if (element is FunctionElement) {
+      FunctionElement functionElement = element;
+      if (functionElement.patch != null) element = functionElement.patch;
+    }
+    return element.getCompilationUnit().script.file;
+  }
+}
+
+/**
+ * A tree visitor that builds [IrNodes]. The visit methods add statements using
+ * to the [builder] and return the last added statement for trees that represent
+ * an expression.
+ */
+class IrNodeBuilderVisitor extends ResolvedVisitor<IrNode> {
+  final SourceFile sourceFile;
+
+  IrNodeBuilderVisitor(
+      TreeElements elements,
+      Compiler compiler,
+      this.sourceFile)
+    : super(elements, compiler);
+
+  IrBuilder builder;
+
+  /**
+   * Builds the [IrFunction] for a function element. In case the function
+   * uses features that cannot be expressed in the IR, this function returns
+   * [:null:].
+   */
+  IrFunction buildMethod(FunctionElement functionElement) {
+    return nullIfGiveup(() => buildMethodInternal(functionElement));
+  }
+
+  IrFunction buildMethodInternal(FunctionElement functionElement) {
+    assert(invariant(functionElement, functionElement.isImplementation));
+    FunctionExpression function = functionElement.parseNode(compiler);
+    assert(function != null);
+    assert(!function.modifiers.isExternal());
+    assert(elements[function] != null);
+
+    int endPosition = function.getEndToken().charOffset;
+    int namePosition = elements[function].position().charOffset;
+    IrFunction result = new IrFunction(
+        nodePosition(function), endPosition, namePosition, <IrNode>[]);
+    builder = new IrBuilder(this);
+    builder.enterBlock();
+    if (function.hasBody()) {
+      function.body.accept(this);
+      ensureReturn(function);
+      result.statements
+        ..addAll(builder.constants.values)
+        ..addAll(builder.statements);
+    }
+    builder.exitBlock();
+    return result;
+  }
+
+  ConstantSystem get constantSystem => compiler.backend.constantSystem;
+
+  /* int | PositionWithIdentifierName */ nodePosition(Node node) {
+    Token token = node.getBeginToken();
+    if (token.isIdentifier()) {
+      return new PositionWithIdentifierName(token.charOffset, token.value);
+    } else {
+      return token.charOffset;
+    }
+  }
+
+  /**
+   * Add an explicit [:return null:] for functions that don't have a return
+   * statement on each branch. This includes functions with an empty body,
+   * such as [:foo(){ }:].
+   */
+  void ensureReturn(FunctionExpression node) {
+    if (builder.returnOnAllBranches) return;
+    IrConstant nullValue =
+        builder.addConstant(constantSystem.createNull(), node);
+    builder.addStatement(new IrReturn(nodePosition(node), nullValue));
+  }
+
+  IrNode visitBlock(Block node) {
+    for (Node n in node.statements.nodes) {
+      n.accept(this);
+    }
+  }
+
+  IrNode visitReturn(Return node) {
+    IrNode value;
+    if (node.expression == null) {
+      if (node.beginToken.value == 'native') return giveup();
+      value = builder.addConstant(constantSystem.createNull(), node);
+    } else {
+      value = node.expression.accept(this);
+    }
+    builder.branchReturns();
+    return builder.addStatement(new IrReturn(nodePosition(node), value));
+  }
+
+  IrConstant visitLiteralBool(LiteralBool node) =>
+      builder.addConstant(constantSystem.createBool(node.value), node);
+
+  IrConstant visitLiteralDouble(LiteralDouble node) =>
+      builder.addConstant(constantSystem.createDouble(node.value), node);
+
+  IrConstant visitLiteralInt(LiteralInt node) =>
+      builder.addConstant(constantSystem.createInt(node.value), node);
+
+  IrConstant visitLiteralString(LiteralString node) =>
+      builder.addConstant(
+          constantSystem.createString(node.dartString, node), node);
+
+  IrConstant visitLiteralNull(LiteralNull node) =>
+      builder.addConstant(constantSystem.createNull(), node);
+
+//  TODO(lry): other literals.
+//  IrNode visitLiteralList(LiteralList node) => visitExpression(node);
+//  IrNode visitLiteralMap(LiteralMap node) => visitExpression(node);
+//  IrNode visitLiteralMapEntry(LiteralMapEntry node) => visitNode(node);
+//  IrNode visitLiteralSymbol(LiteralSymbol node) => visitExpression(node);
+
+  IrNode visitAssert(Send node) {
+    return giveup();
+  }
+
+  IrNode visitClosureSend(Send node) {
+    return giveup();
+  }
+
+  IrNode visitDynamicSend(Send node) {
+    return giveup();
+  }
+
+  IrNode visitGetterSend(Send node) {
+    return giveup();
+  }
+
+  IrNode visitOperatorSend(Send node) {
+    return giveup();
+  }
+
+  IrNode visitStaticSend(Send node) {
+    return giveup();
+  }
+
+  IrNode visitSuperSend(Send node) {
+    return giveup();
+  }
+
+  IrNode visitTypeReferenceSend(Send node) {
+    return giveup();
+  }
+
+  static final String ABORT_IRNODE_BUILDER = "IrNode builder aborted";
+
+  IrNode giveup() => throw ABORT_IRNODE_BUILDER;
+
+  IrNode nullIfGiveup(IrNode action()) {
+    try {
+      return action();
+    } catch(e) {
+      if (e == ABORT_IRNODE_BUILDER) return null;
+      rethrow;
+    }
+  }
+
+  void internalError(String reason, {Node node}) {
+    giveup();
+  }
+}
+
+class IrBuilder {
+  final IrNodeBuilderVisitor visitor;
+  IrBuilder(this.visitor);
+
+  // Statements lists for nested blocks.
+  List<List<IrNode>> statementsList = <List<IrNode>>[];
+  List<IrNode> get statements => statementsList.last;
+
+  // TODO(lry): Need to fix this once we actually have branching. Probably
+  // this will be handled by the LocalsHandler, not here.
+  List<bool> returnOnAllBranchesList = <bool>[];
+  bool get returnOnAllBranches => returnOnAllBranchesList.last;
+  void branchReturns() {
+    returnOnAllBranchesList[returnOnAllBranchesList.length - 1] = true;
+  }
+
+  Map<Constant, IrConstant> constants = <Constant, IrConstant>{};
+
+  IrConstant addConstant(Constant value, Node node) {
+    return constants.putIfAbsent(
+      value, () => new IrConstant(visitor.nodePosition(node), value));
+  }
+
+  IrNode addStatement(IrNode statement) {
+    statements.add(statement);
+    return statement;
+  }
+
+  void enterBlock() {
+    statementsList.add(<IrNode>[]);
+    returnOnAllBranchesList.add(false);
+  }
+
+  void exitBlock() {
+    statementsList.removeLast();
+    returnOnAllBranchesList.removeLast();
+  }
+}