Only emit typeguards if we think they are valuable.

frog/tests/leg/src/TypeInferenceTest.dart

 // Copyright (c) 2011, 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("compiler_helper.dart");
 
 final String TEST_ONE = @"""
 sum(param0, param1) {
   var sum = 0;
   for (var i = param0; i < param1; i += 1) sum = sum + i;
   return sum;
 }
 """;
 
 final String TEST_TWO = @"""
 foo(int param0) {
   return -param0;
 }
 """;
 
+final String TEST_TWO_WITH_BAILOUT = @"""
+foo(int param0) {
+  var t;
+  for (int i = 0; i < 1; i++) {
+    t = -param0;
+  }
+  return t;
+}
+""";
+
 final String TEST_THREE = @"""
 foo(c) {
   for (int i = 0; i < 10; i++) print(c[i]);
 }
 """;
 
 final String TEST_FOUR = @"""
 foo(String c) {
   print(c[0]); // Force a type guard.
   while (true) print(c.length);
 }
 """;
 
 final String TEST_FIVE = @"""
 foo(a) {
   a[0] = 1;
   print(a[1]);
 }
 """;
 
+final String TEST_FIVE_WITH_BAILOUT = @"""
+foo(a) {
+  for (int i = 0; i < 1; i++) {
+    a[0] = 1;
+    print(a[1]);
+  }
+}
+""";
+
 final String TEST_SIX = @"""
-main(a) {
+foo(a) {
   print(a[0]);
   while (true) {
     a[0] = a[1];
   }
 }
 """;
 
 main() {
   String generated = compile(TEST_ONE, 'sum');
 
   RegExp regexp = new RegExp("sum = \\(?$anyIdentifier \\+ $anyIdentifier\\)?");
   Expect.isTrue(regexp.hasMatch(generated));
 
   regexp = const RegExp("typeof param1 !== 'number'");
   Expect.isTrue(regexp.hasMatch(generated));
 
   generated = compile(TEST_TWO, 'foo');
   regexp = new RegExp(getNumberTypeCheck('param0'));
+  Expect.isTrue(!regexp.hasMatch(generated));
+
+  regexp = const RegExp('-param0');
+  Expect.isTrue(!regexp.hasMatch(generated));
+
+  generated = compile(TEST_TWO_WITH_BAILOUT, 'foo');
+  regexp = new RegExp(getNumberTypeCheck('param0'));
   Expect.isTrue(regexp.hasMatch(generated));
 
   regexp = const RegExp('-param0');
   Expect.isTrue(regexp.hasMatch(generated));
 
   generated = compile(TEST_THREE, 'foo');
   regexp = new RegExp("c[$anyIdentifier]");
   Expect.isTrue(regexp.hasMatch(generated));
 
   generated = compile(TEST_FOUR, 'foo');
   regexp = new RegExp("c.length");
   Expect.isTrue(regexp.hasMatch(generated));
 
   generated = compile(TEST_FIVE, 'foo');
   regexp = const RegExp('a.constructor !== Array');
+  Expect.isTrue(!regexp.hasMatch(generated));
+  Expect.isTrue(generated.contains('index'));
+  Expect.isTrue(generated.contains('indexSet'));
+
+  generated = compile(TEST_FIVE_WITH_BAILOUT, 'foo');
+  regexp = const RegExp('a.constructor !== Array');
   Expect.isTrue(regexp.hasMatch(generated));
   Expect.isTrue(!generated.contains('index'));
   Expect.isTrue(!generated.contains('indexSet'));
 
-  generated = compile(TEST_FIVE, 'foo');
+  generated = compile(TEST_SIX, 'foo');
   regexp = const RegExp('a.constructor !== Array');
   Expect.isTrue(regexp.hasMatch(generated));
   Expect.isTrue(!generated.contains('index'));
   Expect.isTrue(!generated.contains('indexSet'));
 }