Integrated: 8336702: C2 compilation fails with "all memory state should have been processed" assert

[Roland Westrelin]

On Mon, 16 Sep 2024 08:34:44 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> When converting a `LongCountedLoop` into a loop nest, c2 needs jvm
> state to add predicates to the inner loop. For that, it peels an
> iteration of the loop and uses the state of the safepoint at the end
> of the loop. That's only legal if there's no side effect between the
> safepoint and the backedge that goes back into the loop. The assert
> failure here happens in code that checks that.
> 
> That code compares the memory states at the safepoint and at the
> backedge. If they are the same then there's no side effect. To check
> consistency, the `MergeMem` at the safepoint is cloned. As the logic
> iterates over the backedge state, it clears every component of the
> state it encounters from the `MergeMem`. Once done, the cloned
> `MergeMem` should be "empty". In the case of this failure, no side
> effect is found but the cloned `MergeMem` is not empty. That happens
> because of EA: it adds edges to the `MergeMem` at the safepoint that
> it doesn't add to the backedge `Phis`.
> 
> So it's the verification code that fails and I propose dealing with
> this by ignoring memory state added by EA in the verification code.

This pull request has now been integrated.

Changeset: ecc77a5b
Author:    Roland Westrelin <roland at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/ecc77a5b4a84c84ffa1580174872af6df3a4f6ca
Stats:     75 lines in 2 files changed: 73 ins; 0 del; 2 mod

8336702: C2 compilation fails with "all memory state should have been processed" assert

Reviewed-by: thartmann, chagedorn

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PR: https://git.openjdk.org/jdk/pull/21009