RFR: 8267399: C2: java/text/Normalizer/ConformanceTest.java test failed with assertion [v2]

[Vladimir Kozlov]

On Tue, 15 Jun 2021 09:30:07 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> This was found with Shenandoah but has nothing specific to Shenandoah.
>> 
>> For the inner loop of the test case:
>> 
>> - the loop limit, len, is known to be either 1 or 2. As a consequence
>>   the type of the iv phi is set to [0..2].
>> 
>> - range check elimination is applied which causes the pre/main/post
>>   loops to be added and the limit of the main loop to be adjusted. C2
>>   computes the limit of the main loop as TypeINT:INT.
>> 
>> - the main loop is peeled. So now the type of the iv phi is 2 and it
>>   constant folds. Because the main loop limit has type TypeInt::INT,
>>   the exit condition of the loop doesn't constant fold. But the loop
>>   no longer has the shape of a counted loop because the iv phi doesn't
>>   exist anymore.
>> 
>> The crash then occurs when some other loop opts is attempted and loop
>> strip mining verification code checks that the shape of the main loop
>> is that of a counted loop.
>> 
>> The fix I propose is to add a CastII at range elimination time that
>> captures the bounds of the limit before RC is applied. This way the
>> type of the limit is not lost and the main loop backbranch can be
>> properly eliminated in the chain of events above.
>
> Roland Westrelin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   comment

Good.

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Marked as reviewed by kvn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/4388