dart2dart: Restore loops with conditions and updates in backend.

sdk/lib/_internal/compiler/implementation/dart_backend/tree_tracer.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 dart_backend.tracer;
 
 import 'dart:async' show EventSink;
 import '../tracer.dart';
 import 'dart_tree.dart';
 
 class Block {
   int index;
-  final List<Statement> statements = <Statement>[];
+  final Label label;
+  /// Mixed list of [Statement] and [Block].
+  /// A [Block] represents a synthetic goto statement.
+  final List statements = [];
   final List<Block> predecessors = <Block>[];
   final List<Block> successors = <Block>[];
 
   String get name => 'B$index';
 
+  Block([this.label]);
+
   void addEdgeTo(Block successor) {
     successors.add(successor);
     successor.predecessors.add(this);
   }
 }
 
 class BlockCollector extends Visitor {
   // Accumulate a list of blocks.  The current block is the last block in
   // the list.
   final List<Block> blocks = [new Block()..index = 0];
 
   // Map tree [Label]s (break or continue targets) and [Statement]s
   // (if targets) to blocks.
   final Map<Label, Block> breakTargets = <Label, Block>{};
   final Map<Label, Block> continueTargets = <Label, Block>{};
   final Map<Statement, Block> ifTargets = <Statement, Block>{};
 
   void _addStatement(Statement statement) {
     blocks.last.statements.add(statement);
   }
+  void _addGotoStatement(Block target) {
+    blocks.last.statements.add(target);
+  }
 
   void _addBlock(Block block) {
     block.index = blocks.length;
     blocks.add(block);
   }
 
   void collect(FunctionDefinition function) {
     visitStatement(function.body);
   }
 
   visitVariable(Variable node) {}
   visitInvokeStatic(InvokeStatic node) {}
   visitInvokeMethod(InvokeMethod node) {}
   visitInvokeConstructor(InvokeConstructor node) {}
   visitConcatenateStrings(ConcatenateStrings node) {}
   visitLiteralList(LiteralList node) {}
   visitLiteralMap(LiteralMap node) {}
   visitInvokeConstConstructor(InvokeConstConstructor node) {}
   visitConstant(Constant node) {}
   visitConditional(Conditional node) {}
   visitLogicalOperator(LogicalOperator node) {}
   visitNot(Not node) {}
 
   visitLabeledStatement(LabeledStatement node) {
-    Block target = new Block();
+    Block target = new Block(node.label);
     breakTargets[node.label] = target;
     visitStatement(node.body);
     _addBlock(target);
     visitStatement(node.next);
   }
 
   visitAssign(Assign node) {
     _addStatement(node);
     visitStatement(node.next);
   }
@@ skipping 19 matching lines @@
     ifTargets[node.thenStatement] = thenTarget;
     ifTargets[node.elseStatement] = elseTarget;
     blocks.last.addEdgeTo(thenTarget);
     blocks.last.addEdgeTo(elseTarget);
     _addBlock(thenTarget);
     visitStatement(node.thenStatement);
     _addBlock(elseTarget);
     visitStatement(node.elseStatement);
   }
 
-  visitWhile(While node) {
+  visitWhileTrue(WhileTrue node) {
     Block continueTarget = new Block();
+    _addGotoStatement(continueTarget);
+
     continueTargets[node.label] = continueTarget;
     blocks.last.addEdgeTo(continueTarget);
     _addBlock(continueTarget);
     _addStatement(node);
     visitStatement(node.body);
   }
 
+  visitWhileCondition(WhileCondition node) {
+    Block whileBlock = new Block();
+    _addGotoStatement(whileBlock);
+
+    _addBlock(whileBlock);
+    _addStatement(node);
+    whileBlock.statements.add(node);
+    blocks.last.addEdgeTo(whileBlock);
+
+    Block bodyBlock = new Block();
+    Block nextBlock = new Block();
+    whileBlock.addEdgeTo(bodyBlock);
+    whileBlock.addEdgeTo(nextBlock);
+
+    continueTargets[node.label] = bodyBlock;
+    _addBlock(bodyBlock);
+    visitStatement(node.body);
+
+    _addBlock(nextBlock);
+    visitStatement(node.next);
+
+    ifTargets[node.body] = bodyBlock;
+    ifTargets[node.next] = nextBlock;
+  }
+
   visitExpressionStatement(ExpressionStatement node) {
     _addStatement(node);
     visitStatement(node.next);
   }
 }
 
-class TreeTracer extends TracerUtil with Visitor {
+class TreeTracer extends TracerUtil with StatementVisitor {
   final EventSink<String> output;
 
   TreeTracer(this.output);
 
   Names names;
   BlockCollector collector;
   int statementCounter;
 
   void traceGraph(String name, FunctionDefinition function) {
     names = new Names();
@@ skipping 17 matching lines @@
       printProperty("successors", block.successors.map((b) => b.name));
       printEmptyProperty("xhandlers");
       printEmptyProperty("flags");
       tag("states", () {
         tag("locals", () {
           printProperty("size", 0);
           printProperty("method", "None");
         });
       });
       tag("HIR", () {
-        block.statements.forEach(visitStatement);
+        if (block.label != null) {
+          printStatement(null,
+              "Label ${block.name}, useCount=${block.label.useCount}");
+        }
+        block.statements.forEach(visitBlockMember);
       });
     });
   }
 
+  void visitBlockMember(member) {
+    if (member is Block) {
+      printStatement(null, "goto block B${member.name}");
+    } else {
+      assert(member is Statement);
+      visitStatement(member);
+    }
+  }
+
   void printStatement(String name, String contents) {
     int bci = 0;
     int uses = 0;
     if (name == null) {
       name = 'x${statementCounter++}';
     }
     addIndent();
     add("$bci $uses $name $contents <|@\n");
   }
 
-  visitVariable(Variable node) {
-    printStatement(null, "dead-use ${names.varName(node)}");
-  }
-
-  visitInvokeStatic(InvokeStatic node) {
-    printStatement(null, expr(node));
-  }
-
-  visitConstant(Constant node) {
-    printStatement(null, "dead-use ${node.value}");
-  }
-
   visitLabeledStatement(LabeledStatement node) {
     // These do not get added to a block's list of statements.
   }
 
   visitAssign(Assign node) {
     String name = names.varName(node.variable);
     String rhs = expr(node.definition);
     printStatement(name, "let $name = $rhs");
   }
 
-  visitInvokeMethod(InvokeMethod node) {
-    printStatement(null, expr(node));
-  }
-
-  visitInvokeConstructor(InvokeConstructor node) {
-    printStatement(null, expr(node));
-  }
-
-  visitConcatenateStrings(ConcatenateStrings node) {
-    printStatement(null, expr(node));
-  }
-
-  visitLiteralList(LiteralList node) {
-    printStatement(null, expr(node));
-  }
-
-  visitLiteralMap(LiteralMap node) {
-    printStatement(null, expr(node));
-  }
-
-  visitInvokeConstConstructor(InvokeConstConstructor node) {
-    printStatement(null, expr(node));
-  }
-
-  visitConditional(Conditional node) {
-    printStatement(null, expr(node));
-  }
-
-  visitLogicalOperator(LogicalOperator node) {
-    printStatement(null, expr(node));
-  }
-
-  visitNot(Not node) {
-    printStatement(null, expr(node));
-  }
-
   visitReturn(Return node) {
     printStatement(null, "return ${expr(node.value)}");
   }
 
   visitBreak(Break node) {
     printStatement(null, "break ${collector.breakTargets[node.target].name}");
   }
 
   visitContinue(Continue node) {
     printStatement(null,
         "continue ${collector.breakTargets[node.target].name}");
   }
 
   visitIf(If node) {
     String condition = expr(node.condition);
     String thenTarget = collector.ifTargets[node.thenStatement].name;
     String elseTarget = collector.ifTargets[node.elseStatement].name;
     printStatement(null, "if $condition then $thenTarget else $elseTarget");
   }
 
-  visitWhile(While node) {
+  visitWhileTrue(WhileTrue node) {
     printStatement(null, "while true do");
   }
 
+  visitWhileCondition(WhileCondition node) {
+    String bodyTarget = collector.ifTargets[node.body].name;
+    String nextTarget = collector.ifTargets[node.next].name;
+    printStatement(null, "while ${expr(node.condition)}");
+    printStatement(null, "do $bodyTarget");
+    printStatement(null, "then $nextTarget" );
+  }
+
   visitExpressionStatement(ExpressionStatement node) {
-    visitExpression(node.expression);
+    printStatement(null, expr(node.expression));
   }
 
   String expr(Expression e) {
     return e.accept(new SubexpressionVisitor(names));
   }
 }
 
-class SubexpressionVisitor extends Visitor<String, String> {
+class SubexpressionVisitor extends ExpressionVisitor<String> {
   Names names;
 
   SubexpressionVisitor(this.names);
 
   String visitVariable(Variable node) {
     return names.varName(node);
   }
 
   String formatArguments(Invoke node) {
     List<String> args = new List<String>();
@@ skipping 92 matching lines @@
   }
 
   String visitNot(Not node) {
     String operand = visitExpression(node.operand);
     if (usesInfixNotation(node.operand)) {
       operand = '($operand)';
     }
     return '!$operand';
   }
 
-  // Note: There should not be statements in the context of expressions.
-  String visitStatement(Statement node) {
-    return "$node statement in expression context";
-  }
-
-  String visitLabeledStatement(LabeledStatement node) => visitStatement(node);
-  String visitAssign(Assign node) => visitStatement(node);
-  String visitReturn(Return node) => visitStatement(node);
-  String visitBreak(Break node) => visitStatement(node);
-  String visitContinue(Continue node) => visitStatement(node);
-  String visitIf(If node) => visitStatement(node);
-  String visitWhile(While node) => visitStatement(node);
-  String visitExpressionStatement(ExpressionStatement node) {
-    return visitStatement(node);
-  }
 }
 
 /**
  * Invents (and remembers) names for Variables that do not have an associated
  * identifier.
  *
  * In case a variable is named v0, v1, etc, it may be assigned a different
  * name to avoid clashing with a previously synthesized variable name.
  */
 class Names {
@@ skipping 10 matching lines @@
       }
       while (name == null || _usedNames.contains(name)) {
         name = "v${_counter++}";
       }
       _names[v] = name;
       _usedNames.add(name);
     }
     return name;
   }
 }