Uploaded image for project: 'JDK'
  1. JDK
  2. JDK-8058199

Code generation problem with javac skipping a checkcast instruction

    Details

    • Subcomponent:
    • Resolved In Build:
      b36
    • CPU:
      x86
    • OS:
      os_x
    • Verification:
      Verified

      Backports

        Description

        FULL PRODUCT VERSION :
        java version "1.8.0_20"
        Java(TM) SE Runtime Environment (build 1.8.0_20-b26)
        Java HotSpot(TM) 64-Bit Server VM (build 25.20-b23, mixed mode)


        ADDITIONAL OS VERSION INFORMATION :
        Darwin dd 13.3.0 Darwin Kernel Version 13.3.0: Tue Jun 3 21:27:35 PDT 2014; root:xnu-2422.110.17~1/RELEASE_X86_64 x86_64

        A DESCRIPTION OF THE PROBLEM :
        Recently I filed an eclipse bug https://bugs.eclipse.org/bugs/show_bug.cgi?id=442929. Srikanth Sankaran and Timo Kinnunen investigated that it is likely a javac bug.

        In a nutshell, methods which create generic arrays internally and then let those arrays escape from the generic type's scope are unusable for their callers - but javac misses to type check these cases.

        Please follow the above link to get additional examples and a detailed description of the bug.

        STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
        Please compile and run the example source code provided here as follows:

        $ javac MissingTypeCheck.java
        $ java MissingTypeCheck

        The program should terminate with return code 0 (no error).

        EXPECTED VERSUS ACTUAL BEHAVIOR :
        EXPECTED -
        Javac is expected to generate byte code which performs an additional type check. When running the example source code provided here, an exception similar to this should be thrown:

        Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;
        at MissingTypeCheck.main(MissingTypeCheck.java:11)
        ACTUAL -
        No type check is performed / no exception is thrown.

        REPRODUCIBILITY :
        This bug can be reproduced always.

        ---------- BEGIN SOURCE ----------
        // credits for this test go to Timo Kinnunen
        class MissingTypeCheck {

        public static void main(String[] args) {

        // -- does not throw compiled with javac (correct)
        MissingTypeCheck.<String> newArray();

        // -- does not throw compiled with javac (NOT CORRECT)
        // -- JAVAC SHOULD PERFORM A TYPE CHECK HERE
        assertNothing(MissingTypeCheck.<String> newArray());

        // -- throws compiled with javac (correct)
        // String[] hopeless = newArray();
        }

        static <T> void assertNothing(T actual) {
        /* nada */
        }

        static <T> T[] newArray() {
        @SuppressWarnings("unchecked")
        T[] array = (T[]) new Object[0];
        return array;
        }
        }
        ---------- END SOURCE ----------

          Attachments

            Issue Links

              Activity

                People

                • Assignee:
                  mcimadamore Maurizio Cimadamore
                  Reporter:
                  webbuggrp Webbug Group
                • Votes:
                  0 Vote for this issue
                  Watchers:
                  5 Start watching this issue

                  Dates

                  • Created:
                    Updated:
                    Resolved: