RFR: 8263303: C2 compilation fails with assert(found_sfpt) failed: no node in loop that's not input to safepoint [v2]

[Vladimir Kozlov]

On Wed, 9 Jun 2021 09:09:42 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> The loop strip mining verification code catches a node which is pinned
>> in the outer strip mined loop but not referenced from the safepoint
>> node.
>> 
>> The test case is an example of how this could happen. The array[i]
>> load is referenced from the safepoint initially through:
>> 
>> (j - 10) * array[i]
>> 
>> It is sunk out of the inner loop and pinned in the outer loop. A
>> following loop opts round causes j - 10 to constant fold to 0 and as a
>> consequence the array load is no longer referenced from the safepoint
>> but pinned in the outer strip mined loop.
>> 
>> I tried to find a way to preserve the invariant that all nodes in the
>> outer strip mined loop are referenced from the safepoint but found no
>> robust way for that. So the fix removes that part of the verification
>> code.
>> 
>> This requires loop cloning code to be adjusted for nodes pinned in the
>> outer strip mined loop but not referenced from the safepoint.
>
> Roland Westrelin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove useless line from test

Let me run tests before you push.

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Marked as reviewed by kvn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/4278