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() {
+    // TODO(lry): support checked-mode checks.
+    if (compiler.enableTypeAssertions) return;
+
+    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 canBuild(Element element) {
+    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;
+
+    if (compiler.backend is JavaScriptBackend) {
+      JavaScriptBackend backend = compiler.backend;
+      if (backend.isInterceptedMethod(element)) return false;

[karlklose, 2013/11/22 08:01:06]

Consider storing compiler.backend in a field. (of type backend). The is test for
that field should then promote the static type to JavaSCriptBackend.

In general we should not need this special casing for the JS backend but instead
add an abstraction to Backend.

[lukas, 2013/11/22 11:51:34]

Cleaned up as discussed offline. For now we abort early when not targeting
Javascript.

+    }
+
+    return true;
+  }
+
+  void unlinkTreeAndToken(element) {
+    // TODO(lry): Make the dart backend generate code from IR nodes.
+    if (compiler.backend is JavaScriptBackend) {
+      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();
+  }
+}