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Side by Side Diff: pkg/compiler/lib/src/dart_backend/loop_rewriter.dart

Issue 693183006: Revert "Move dart2js from sdk/lib/_internal/compiler to pkg/compiler" (Closed) Base URL: https://dart.googlecode.com/svn/branches/bleeding_edge/dart
Patch Set: Created 6 years, 1 month ago
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1 // Copyright (c) 2014, the Dart project authors. Please see the AUTHORS file
2 // for details. All rights reserved. Use of this source code is governed by a
3 // BSD-style license that can be found in the LICENSE file.
4
5 library loop_rewriter;
6
7 import 'tree_ir_nodes.dart';
8
9 /// Rewrites [WhileTrue] statements with an [If] body into a [WhileCondition],
10 /// in situations where only one of the branches contains a [Continue] to the
11 /// loop. Schematically:
12 ///
13 /// L:
14 /// while (true) {
15 /// if (E) {
16 /// S1 (has references to L)
17 /// } else {
18 /// S2 (has no references to L)
19 /// }
20 /// }
21 /// ==>
22 /// L:
23 /// while (E) {
24 /// S1
25 /// };
26 /// S2
27 ///
28 /// A similar transformation is used when S2 occurs in the 'then' position.
29 ///
30 /// Note that the above pattern needs no iteration since nested ifs
31 /// have been collapsed previously in the [StatementRewriter] phase.
32 class LoopRewriter extends RecursiveVisitor {
33
34 Set<Label> usedContinueLabels = new Set<Label>();
35
36 void rewrite(FunctionDefinition function) {
37 if (function.isAbstract) return;
38
39 function.body = visitStatement(function.body);
40 }
41
42 Statement visitLabeledStatement(LabeledStatement node) {
43 node.body = visitStatement(node.body);
44 node.next = visitStatement(node.next);
45 return node;
46 }
47
48 Statement visitAssign(Assign node) {
49 // Clean up redundant assignments left behind in the previous phase.
50 if (node.variable == node.definition) {
51 --node.variable.readCount;
52 --node.variable.writeCount;
53 return visitStatement(node.next);
54 }
55 visitExpression(node.definition);
56 node.next = visitStatement(node.next);
57 return node;
58 }
59
60 Statement visitReturn(Return node) {
61 visitExpression(node.value);
62 return node;
63 }
64
65 Statement visitBreak(Break node) {
66 return node;
67 }
68
69 Statement visitContinue(Continue node) {
70 usedContinueLabels.add(node.target);
71 return node;
72 }
73
74 Statement visitIf(If node) {
75 visitExpression(node.condition);
76 node.thenStatement = visitStatement(node.thenStatement);
77 node.elseStatement = visitStatement(node.elseStatement);
78 return node;
79 }
80
81 Statement visitWhileTrue(WhileTrue node) {
82 assert(!usedContinueLabels.contains(node.label));
83 if (node.body is If) {
84 If body = node.body;
85 body.thenStatement = visitStatement(body.thenStatement);
86 bool thenHasContinue = usedContinueLabels.remove(node.label);
87 body.elseStatement = visitStatement(body.elseStatement);
88 bool elseHasContinue = usedContinueLabels.remove(node.label);
89 if (thenHasContinue && !elseHasContinue) {
90 node.label.binding = null; // Prepare to rebind the label.
91 return new WhileCondition(
92 node.label,
93 body.condition,
94 body.thenStatement,
95 body.elseStatement);
96 } else if (!thenHasContinue && elseHasContinue) {
97 node.label.binding = null;
98 return new WhileCondition(
99 node.label,
100 new Not(body.condition),
101 body.elseStatement,
102 body.thenStatement);
103 }
104 } else {
105 node.body = visitStatement(node.body);
106 usedContinueLabels.remove(node.label);
107 }
108 return node;
109 }
110
111 Statement visitWhileCondition(WhileCondition node) {
112 // Note: not reachable but the implementation is trivial
113 visitExpression(node.condition);
114 node.body = visitStatement(node.body);
115 node.next = visitStatement(node.next);
116 return node;
117 }
118
119 Statement visitExpressionStatement(ExpressionStatement node) {
120 visitExpression(node.expression);
121 node.next = visitStatement(node.next);
122 return node;
123 }
124
125 Statement visitFunctionDeclaration(FunctionDeclaration node) {
126 new LoopRewriter().rewrite(node.definition);
127 node.next = visitStatement(node.next);
128 return node;
129 }
130
131 void visitFunctionExpression(FunctionExpression node) {
132 new LoopRewriter().rewrite(node.definition);
133 }
134 }
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