Reapply "Added for-loop variable tracking and regular closures/initializers captured variable track…

pkg/compiler/lib/src/js_model/closure_visitors.dart

+// Copyright (c) 2017, 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.
+
+import 'package:kernel/ast.dart' as ir;
+
+import '../closure.dart';
+import '../elements/entities.dart';
+import 'closure.dart';
+import '../kernel/element_map.dart';
+
+/// This builder walks the code to determine what variables are captured/free at
+/// various points to build ClosureScope that can respond to queries
+/// about how a particular variable is being used at any point in the code.
+class ClosureScopeBuilder extends ir.Visitor {
+  /// A map of each visited call node with the associated information about what
+  /// variables are captured/used. Each ir.Node key corresponds to a scope that
+  /// was encountered while visiting a closure (initially called through
+  /// [translateLazyIntializer] or [translateConstructorOrProcedure]).
+  Map<ir.Node, ClosureScope> _closureInfoMap = <ir.Node, ClosureScope>{};
+
+  /// A map of the nodes that we have flagged as necessary to generate closure
+  /// classes for in a later stage. We map that node to information ascertained
+  /// about variable usage in the surrounding scope.
+  Map<ir.Node /* ir.Field | ir.FunctionNode */, ScopeInfo> _closuresToGenerate =
+      <ir.Node, ScopeInfo>{};
+
+  /// The local variables that have been declared in the current scope.
+  List<ir.VariableDeclaration> _scopeVariables;
+
+  /// Pointer to the context in which this closure is executed.
+  /// For example, in the expression `var foo = () => 3 + i;`, the executable
+  /// context as we walk the nodes in that expression is the ir.Field `foo`.
+  ir.Node _executableContext;
+
+  /// A flag to indicate if we are currently inside a closure.
+  bool _isInsideClosure = false;
+
+  /// Pointer to the original node where this closure builder started.
+  ir.Node _outermostNode;
+
+  /// Keep track of the mutated local variables so that we don't need to box
+  /// non-mutated variables.
+  Set<ir.VariableDeclaration> _mutatedVariables =
+      new Set<ir.VariableDeclaration>();
+
+  /// The set of variables that are accessed in some form, whether they are
+  /// mutated or not.
+  Set<ir.VariableDeclaration> _capturedVariables =
+      new Set<ir.VariableDeclaration>();
+
+  /// If true, the visitor is currently traversing some nodes that are inside a
+  /// try block.
+  bool _inTry = false;
+
+  /// Lookup the local entity that corresponds to a kernel variable declaration.
+  final KernelToLocalsMap _localsMap;
+
+  /// The current scope we are in.
+  KernelScopeInfo _currentScopeInfo;
+
+  final KernelToElementMap _kernelToElementMap;
+
+  ClosureScopeBuilder(this._closureInfoMap, this._closuresToGenerate,
+      this._localsMap, this._kernelToElementMap);
+
+  /// Update the [ClosureScope] object corresponding to
+  /// this node if any variables are captured.
+  void attachCapturedScopeVariables(ir.Node node) {
+    Set<Local> capturedVariablesForScope = new Set<Local>();
+
+    for (ir.VariableDeclaration variable in _scopeVariables) {
+      // No need to box non-assignable elements.
+      if (variable.isFinal || variable.isConst) continue;
+      if (!_mutatedVariables.contains(variable)) continue;
+      if (_capturedVariables.contains(variable)) {
+        capturedVariablesForScope.add(_localsMap.getLocal(variable));
+      }
+    }
+    if (!capturedVariablesForScope.isEmpty) {
+      ThisLocal thisLocal = null;
+      if (node is ir.Member && node.isInstanceMember) {
+        if (node is ir.Procedure) {
+          thisLocal = new ThisLocal(_kernelToElementMap.getMethod(node));
+        } else if (node is ir.Field) {
+          thisLocal = new ThisLocal(_kernelToElementMap.getField(node));
+        }
+      } else if (node is ir.Constructor) {
+        thisLocal = new ThisLocal(_kernelToElementMap.getConstructor(node));
+      }
+
+      Entity context;
+      if (_executableContext is ir.Member) {
+        context = _kernelToElementMap.getMember(_executableContext);
+      } else {
+        context = _kernelToElementMap.getLocalFunction(_executableContext);
+      }
+      _closureInfoMap[node] =
+          new KernelClosureScope(capturedVariablesForScope, context, thisLocal);
+    }
+  }
+
+  /// Perform book-keeping with the current set of local variables that have
+  /// been seen thus far before entering this new scope.
+  void enterNewScope(ir.Node node, Function visitNewScope) {
+    List<ir.VariableDeclaration> oldScopeVariables = _scopeVariables;
+    _scopeVariables = <ir.VariableDeclaration>[];
+    visitNewScope();
+    attachCapturedScopeVariables(node);
+    _mutatedVariables.removeAll(_scopeVariables);
+    _scopeVariables = oldScopeVariables;
+  }
+
+  @override
+  void defaultNode(ir.Node node) {
+    node.visitChildren(this);
+  }
+
+  @override
+  visitTryCatch(ir.TryCatch node) {
+    bool oldInTry = _inTry;
+    _inTry = true;
+    node.visitChildren(this);
+    _inTry = oldInTry;
+  }
+
+  @override
+  visitTryFinally(ir.TryFinally node) {
+    bool oldInTry = _inTry;
+    _inTry = true;
+    node.visitChildren(this);
+    _inTry = oldInTry;
+  }
+
+  @override
+  visitVariableGet(ir.VariableGet node) {
+    _markVariableAsUsed(node.variable);
+  }
+
+  @override
+  visitVariableSet(ir.VariableSet node) {
+    _mutatedVariables.add(node.variable);
+    _markVariableAsUsed(node.variable);
+    node.visitChildren(this);
+  }
+
+  /// Add this variable to the set of free variables if appropriate and add to
+  /// the tally of variables used in try or sync blocks.
+  void _markVariableAsUsed(ir.VariableDeclaration variable) {
+    if (_isInsideClosure && !_inCurrentContext(variable)) {
+      // If the element is not declared in the current function and the element
+      // is not the closure itself we need to mark the element as free variable.
+      // Note that the check on [insideClosure] is not just an
+      // optimization: factories have type parameters as function
+      // parameters, and type parameters are declared in the class, not
+      // the factory.
+      _currentScopeInfo.freeVariables.add(variable);
+    }
+    if (_inTry) {
+      _currentScopeInfo.localsUsedInTryOrSync
+          .add(_localsMap.getLocal(variable));
+    }
+  }
+
+  @override
+  void visitForStatement(ir.ForStatement node) {
+    List<Local> boxedLoopVariables = <Local>[];
+    enterNewScope(node, () {
+      // First visit initialized variables and update steps so we can easily
+      // check if a loop variable was captured in one of these subexpressions.
+      node.variables
+          .forEach((ir.VariableDeclaration variable) => variable.accept(this));
+      node.updates
+          .forEach((ir.Expression expression) => expression.accept(this));
+
+      // Loop variables that have not been captured yet can safely be flagged as
+      // non-mutated, because no nested function can observe the mutation.
+      for (ir.VariableDeclaration variable in node.variables) {
+        if (!_capturedVariables.contains(variable)) {
+          _mutatedVariables.remove(variable);
+        }
+      }
+
+      // Visit condition and body.
+      // This must happen after the above, so any loop variables mutated in the
+      // condition or body are indeed flagged as mutated.
+      if (node.condition != null) node.condition.accept(this);
+      node.body.accept(this);
+
+      // See if we have declared loop variables that need to be boxed.
+      for (ir.VariableDeclaration variable in node.variables) {
+        // Non-mutated variables should not be boxed.  The _mutatedVariables set
+        // gets cleared when `enterNewScope` returns, so check it here.
+        if (_capturedVariables.contains(variable) &&
+            _mutatedVariables.contains(variable)) {
+          boxedLoopVariables.add(_localsMap.getLocal(variable));
+        }
+      }
+    });
+    KernelClosureScope scope = _closureInfoMap[node];
+    if (scope == null) return;
+    _closureInfoMap[node] = new KernelLoopClosureScope(scope.boxedVariables,
+        boxedLoopVariables, scope.context, scope.thisLocal);
+  }
+
+  void visitInvokable(ir.TreeNode node) {
+    bool oldIsInsideClosure = _isInsideClosure;
+    ir.Node oldExecutableContext = _executableContext;
+    KernelScopeInfo oldScopeInfo = _currentScopeInfo;
+
+    // _outermostNode is only null the first time we enter the body of the
+    // field, constructor, or method that is being analyzed.
+    _isInsideClosure = _outermostNode != null;
+    _executableContext = node;
+    if (!_isInsideClosure) {
+      _outermostNode = node;
+    }
+    _currentScopeInfo = new KernelScopeInfo(_nodeToThisLocal(node));
+    _closuresToGenerate[node] = _currentScopeInfo;
+
+    enterNewScope(node, () {
+      node.visitChildren(this);
+    });
+
+    KernelScopeInfo savedScopeInfo = _currentScopeInfo;
+    bool savedIsInsideClosure = _isInsideClosure;
+
+    // Restore old values.
+    _isInsideClosure = oldIsInsideClosure;
+    _currentScopeInfo = oldScopeInfo;
+    _executableContext = oldExecutableContext;
+
+    // Mark all free variables as captured and expect to encounter them in the
+    // outer function.
+    Iterable<ir.VariableDeclaration> freeVariables =
+        savedScopeInfo.freeVariables;
+    assert(freeVariables.isEmpty || savedIsInsideClosure);
+    for (ir.VariableDeclaration freeVariable in freeVariables) {
+      assert(!_capturedVariables.contains(freeVariable));
+      _capturedVariables.add(freeVariable);
+      _markVariableAsUsed(freeVariable);
+    }
+  }
+
+  /// Return true if [variable]'s context is the same as the current executable
+  /// context.
+  bool _inCurrentContext(ir.VariableDeclaration variable) {
+    ir.TreeNode node = variable;
+    while (node != _outermostNode && node != _executableContext) {
+      node = node.parent;
+    }
+    return node == _executableContext;
+  }
+
+  void translateLazyInitializer(ir.Field field) {
+    visitInvokable(field);
+  }
+
+  void translateConstructorOrProcedure(ir.Node constructorOrProcedure) {
+    constructorOrProcedure.accept(this);
+  }
+
+  void visitFunctionNode(ir.FunctionNode functionNode) {
+    visitInvokable(functionNode);
+  }
+
+  /// If [node] is an instance member return the corresponding `this` reference.
+  /// If not, return null.
+  Entity _nodeToThisLocal(
+      ir.TreeNode
+          /*ir.Field|ir.FunctionNode|ir.Constructor|ir.Procedure*/ node) {
+    ir.Node nodeToConvert = node;
+    if (nodeToConvert is ir.Field) {
+      if (!nodeToConvert.isInstanceMember) return null;
+      return new ThisLocal(_kernelToElementMap.getField(nodeToConvert));
+    } else {
+      if (nodeToConvert is ir.FunctionNode) {
+        // Step up one node higher to find the corresponding entity for this
+        // node.
+        nodeToConvert = node.parent;
+      }
+      if (nodeToConvert is ir.Constructor ||
+          (nodeToConvert is ir.Procedure &&
+              nodeToConvert.kind == ir.ProcedureKind.Factory &&
+              nodeToConvert.isInstanceMember)) {
+        return new ThisLocal(_kernelToElementMap.getConstructor(nodeToConvert));
+      } else if (nodeToConvert is ir.Procedure &&
+          nodeToConvert.isInstanceMember) {
+        return new ThisLocal(_kernelToElementMap.getMethod(nodeToConvert));
+      }
+    }
+    return null;
+  }
+}