RFR (S) 8176580: [ppc, s390] CRC32C: wrong checksum result in some cases

[Volker Simonis]

Hi Lutz,

thanks a lot for updating the tests. I think they look much better now.

There's just one more cleanup I'd like to propose. Can you please move
the throw right into the check() function. Just make check() return
void and throw from it if there's a mismatch between the computed and
the expected result. I leave it up to you if you want to pass an extra
error string to check() which will be printed in the case of an error.
I personally don't think that's necessary as it will be evident from
the stack trace which computation failed.

Also the try/catch and rethrow in test_multi() isn't necessary. The
test can be simply terminated by the initial exception.

Thank you and best regards,
Volker


On Fri, Mar 17, 2017 at 10:03 PM, Schmidt, Lutz <lutz.schmidt at sap.com> wrote:
> Hi Volker,
>
> Thanks a lot for your valuable hints.
>
> I have worked some time on the Java test files:
>   TestCRC32.java and TestCRC32C.java are now identical as far as possible.
>   They now throw an exception, should any error be detected.
>   The “reference CRC value” is now used in test_multi() as well.
>   The extra test runs have been removed again.
>   The test methodology is fixed: each result is tested against its reference.
>   The tests now detect the bug introduced with 8175368 and 8175369.
>   No issue is indicated when testing with 8176580.
>   I ran jcheck, and to the best of my ability and knowledge, there is no trailing whitespace.
>   All *.cpp files were left untouched!
>
> The next iteration of the webrev: http://cr.openjdk.java.net/~lucy/webrevs/8176580.02/
>
> Best regards,
> Lutz
>
>
> Dr. Lutz Schmidt | SAP JVM | PI  SAP CP Core | T: +49 (6227) 7-42834
>
>
>
> On 16.03.17, 11:28, "Volker Simonis" <volker.simonis at gmail.com> wrote:
>
>     On Wed, Mar 15, 2017 at 5:55 PM, Schmidt, Lutz <lutz.schmidt at sap.com> wrote:
>     >
>     > Hi Andrew, Volker,
>     >
>     > What do you think about these test enhancements?
>     >   Webrev: http://cr.openjdk.java.net/~lucy/webrevs/8176580.01/
>     >
>     > Please note: the cpp files in the webrev remained unchanged.
>     >
>     > I added some improvements (as I believe) to the TestCRC32(C).java files.
>     >
>     > In some more detail:
>     > The test now calculates a “reference CRC value”, based on a java implementation of the CRC32 algorithm. This reference value is used to verify all other crc values, in particular during initialization and warmup. Three additional test runs check a non-zero offset with –Xint, -Xcomp -XX:-TieredCompilation (C2 only), -Xcomp -XX:+TieredCompilation (C1 + C2).
>     >
>
>     Hi Lutz,
>
>     thanks for updating the tests. I've had a closer look at the tests and
>     realized that they actually can never fail! The check() routine just
>     prints an error message but that will not let the test fail. So I
>     would suggest to throw a runtime exception in the check() routine
>     after the error message was printed.
>
>     I also suggest to do the check during the normal test execution (i.e.
>     in test_multi()) so there's no need for extra test runs.
>
>     Finally, the current test methodology in test_multi() is broken:
>      - it sets the reference by calling CRC from the interpreter which
>     won't work if the intrinsic is also used in the interpreter.
>      - it only compares the reference against the last computation of CRC
>     in the loop which will be the result of the C2 generated code. This
>     misses errors in C1.
>
>     I suggest to use your new, pure Java implementation for the
>     computation of the reference result and compare the reference with the
>     result of calling CRC in every iteration of the loop so we really
>     check all possibilities from interpreter trough C1 to C2.
>
>     Finally, can you please pay attention to not insert trailing
>     whitespace (there was some at line 88 in TestCRC32C.java). You can
>     easily verify this by running jcheck before creating the webrevs.
>
>     Thanks,
>     Volker
>
>     >
>     > Best regards,
>     > Lutz
>     >
>     >
>     > On 15.03.17, 11:50, "Volker Simonis" <volker.simonis at gmail.com> wrote:
>     >
>     >     On Tue, Mar 14, 2017 at 7:05 PM, Andrew Haley <aph at redhat.com> wrote:
>     >     > On 14/03/17 13:12, Schmidt, Lutz wrote:
>     >     >
>     >     >> Yes, one might think of running a test suite subset multiple times
>     >     >> with different parameters. In this case, -Xint and/or –Xcomp were
>     >     >> helpful. Forcing tests to run fully interpreted or fully compiled
>     >     >> helps in cases where a certain function, e.g. an intrinsic, is
>     >     >> invoked via distinct code paths.
>     >     >
>     >     > Right, so your patch should include that change to the test suite.
>     >     >
>     >
>     >     Hi Lutz,
>     >
>     >     I agree with Andrew. We should really fix the tests such that they
>     >     check the correctness of the intrinsics.
>     >
>     >     This may be tricky if all three, the interpreter, the client and the
>     >     server compiler use the same intrinsic implementation. You could
>     >     either copy the pure Java implementation into the test so that you can
>     >     compare the results of the intrinsic operation against it or you can
>     >     switch them off in the compilers with
>     >     "-XX:DisableIntrinsic=_updateBytesCRC32C
>     >     -XX:DisableIntrinsics=_updateDirectByteBufferCRC32C" and compare the
>     >     results. Not sure which solution is more practical, but I would be
>     >     really scared if we wouldn't have these test.
>     >
>     >     Regards,
>     >     Volker
>     >
>     >     > Andrew.
>     >     >
>     >
>     >
>
>