RFR: 8336830: C2: assert(get_loop(lca)->_nest < n_loop->_nest || lca->in(0)->is_NeverBranch()) failed: must not be moved into inner loop [v2]

[Tobias Hartmann]

On Thu, 22 Aug 2024 15:09:19 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> A store is sunk from a counted loop into an enclosing infinite
>> loop. The assert fires because:
>> 
>> 
>> get_loop(lca)->_nest < n_loop->_nest
>> 
>> 
>> is false. That happens because the outer loop was found to be infinite
>> in the current loop opts pass. When that happens, it's not properly
>> attached to the loop tree. The second part of the assert was added to
>> cover a similar case:
>> 
>> 
>> lca->in(0)->is_NeverBranch()
>> 
>> 
>> but it doesn't work in this case bcause lca is not a projection of the
>> `NeverBranch`. It's the exit projection of the counted loop. The fix I
>> propose changes that part of the assert to test that lca is, indeed,
>> in an infinite loop in a way that's robust.
>> 
>> I also removed some code that I believe to be useless following
>> 8335709.
>
> Roland Westrelin has updated the pull request incrementally with one additional commit since the last revision:
> 
>   undo unrelated change

Still good.

-------------

Marked as reviewed by thartmann (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20334#pullrequestreview-2259766162