Avoid critical edge for loop-exits.

tests/language/critical_edge_test.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.
+
+// This test broke dart2js.
+// A compiler must not construct a critical edge on this program.
+
+import "package:expect/expect.dart";
+
+String parse(String uri) {
+  int index = 0;
+  int char = -1;
+
+  void parseAuth() {
+    index;
+    char;
+  }
+
+  int state = 0;
+  while (true) {

[ngeoffray, 2014/06/24 12:39:14]

Seems like the "true" is the only difference. Is it to provoke a different path
in builder.dart? I would add a comment.

[floitsch, 2014/06/24 14:44:38]

It also uses more variables after the loop. This leads to different temporaries
being used. The behavior of the two tests is therefore different.
The first test crashes (array-index == -1), whereas this test returns "bad".

+    char = uri.codeUnitAt(index);
+    if (char == 1234) {
+      state = (index == 0) ? 1 : 2;
+      break;
+    }
+    if (char == 0x3A) {
+      return "good";
+    }
+    index++;
+  }
+
+  if (state == 1) {
+    print(char == 1234);
+    print(index == uri.length);
+  }
+  return "bad";
+}
+
+main() {
+  Expect.equals("good", parse("dart:_foreign_helper"));
+}