If an instruction is known to already by a number, the integer check will try to make it an integer.

tests/compiler/dart2js/type_inference2_test.dart

Index: tests/compiler/dart2js/type_inference2_test.dart
===================================================================
--- tests/compiler/dart2js/type_inference2_test.dart	(revision 10938)
+++ tests/compiler/dart2js/type_inference2_test.dart	(working copy)
@@ -14,7 +14,5 @@
 
 main() {
   String generated = compile(TEST_ONE, 'sum');
-  // We don't want "i = t0" in the loop-update, but i = <id> + 1.
-  RegExp regexp = new RegExp("i = \\(?$anyIdentifier \\+ \\(1\\)\\)?");
-  Expect.isTrue(regexp.hasMatch(generated));
+  Expect.isTrue(generated.contains('++i'));
 }