Add the first phi's input as possible generate-at-use-site.

frog/tests/leg/src/SsaPhiCodegenTest.dart

Index: frog/tests/leg/src/SsaPhiCodegenTest.dart
diff --git a/frog/tests/leg/src/SsaPhiCodegenTest.dart b/frog/tests/leg/src/SsaPhiCodegenTest.dart
index dad164904b8c343f620bec4fa624ad6582914143..6b2b5d633f07ef75686957187247f443ebcb3760 100644
--- a/frog/tests/leg/src/SsaPhiCodegenTest.dart
+++ b/frog/tests/leg/src/SsaPhiCodegenTest.dart
@@ -65,12 +65,12 @@ main() {
   regexp = const RegExp(@"print\(a\)");
   Expect.isTrue(regexp.hasMatch(generated));
 
-  // TODO(ngeoffray): Add live range analysis to the codegen
-  // to make this test pass.
   generated = compile(TEST_TWO, 'main');
   regexp = new RegExp("t = \\(?$anyIdentifier +");
-  Expect.isFalse(regexp.hasMatch(generated));
+  Expect.isTrue(regexp.hasMatch(generated));
 
+  // TODO(ngeoffray): Add live range analysis to the codegen
+  // to make this test pass.
   regexp = new RegExp("i = \\(?$anyIdentifier +");
   Expect.isFalse(regexp.hasMatch(generated));