Revert "Move dart2js from sdk/lib/_internal/compiler to pkg/compiler"

pkg/compiler/lib/src/dart_backend/loop_rewriter.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.
-
-library loop_rewriter;
-
-import 'tree_ir_nodes.dart';
-
-/// Rewrites [WhileTrue] statements with an [If] body into a [WhileCondition],
-/// in situations where only one of the branches contains a [Continue] to the
-/// loop. Schematically:
-///
-///   L:
-///   while (true) {
-///     if (E) {
-///       S1  (has references to L)
-///     } else {
-///       S2  (has no references to L)
-///     }
-///   }
-///     ==>
-///   L:
-///   while (E) {
-///     S1
-///   };
-///   S2
-///
-/// A similar transformation is used when S2 occurs in the 'then' position.
-///
-/// Note that the above pattern needs no iteration since nested ifs
-/// have been collapsed previously in the [StatementRewriter] phase.
-class LoopRewriter extends RecursiveVisitor {
-
-  Set<Label> usedContinueLabels = new Set<Label>();
-
-  void rewrite(FunctionDefinition function) {
-    if (function.isAbstract) return;
-
-    function.body = visitStatement(function.body);
-  }
-
-  Statement visitLabeledStatement(LabeledStatement node) {
-    node.body = visitStatement(node.body);
-    node.next = visitStatement(node.next);
-    return node;
-  }
-
-  Statement visitAssign(Assign node) {
-    // Clean up redundant assignments left behind in the previous phase.
-    if (node.variable == node.definition) {
-      --node.variable.readCount;
-      --node.variable.writeCount;
-      return visitStatement(node.next);
-    }
-    visitExpression(node.definition);
-    node.next = visitStatement(node.next);
-    return node;
-  }
-
-  Statement visitReturn(Return node) {
-    visitExpression(node.value);
-    return node;
-  }
-
-  Statement visitBreak(Break node) {
-    return node;
-  }
-
-  Statement visitContinue(Continue node) {
-    usedContinueLabels.add(node.target);
-    return node;
-  }
-
-  Statement visitIf(If node) {
-    visitExpression(node.condition);
-    node.thenStatement = visitStatement(node.thenStatement);
-    node.elseStatement = visitStatement(node.elseStatement);
-    return node;
-  }
-
-  Statement visitWhileTrue(WhileTrue node) {
-    assert(!usedContinueLabels.contains(node.label));
-    if (node.body is If) {
-      If body = node.body;
-      body.thenStatement = visitStatement(body.thenStatement);
-      bool thenHasContinue = usedContinueLabels.remove(node.label);
-      body.elseStatement = visitStatement(body.elseStatement);
-      bool elseHasContinue = usedContinueLabels.remove(node.label);
-      if (thenHasContinue && !elseHasContinue) {
-        node.label.binding = null; // Prepare to rebind the label.
-        return new WhileCondition(
-            node.label,
-            body.condition,
-            body.thenStatement,
-            body.elseStatement);
-      } else if (!thenHasContinue && elseHasContinue) {
-        node.label.binding = null;
-        return new WhileCondition(
-            node.label,
-            new Not(body.condition),
-            body.elseStatement,
-            body.thenStatement);
-      }
-    } else {
-      node.body = visitStatement(node.body);
-      usedContinueLabels.remove(node.label);
-    }
-    return node;
-  }
-
-  Statement visitWhileCondition(WhileCondition node) {
-    // Note: not reachable but the implementation is trivial
-    visitExpression(node.condition);
-    node.body = visitStatement(node.body);
-    node.next = visitStatement(node.next);
-    return node;
-  }
-
-  Statement visitExpressionStatement(ExpressionStatement node) {
-    visitExpression(node.expression);
-    node.next = visitStatement(node.next);
-    return node;
-  }
-
-  Statement visitFunctionDeclaration(FunctionDeclaration node) {
-    new LoopRewriter().rewrite(node.definition);
-    node.next = visitStatement(node.next);
-    return node;
-  }
-
-  void visitFunctionExpression(FunctionExpression node) {
-    new LoopRewriter().rewrite(node.definition);
-  }
-}