RFR: 8303279: C2 Compiler crash (triggered by Kotlin 1.8.10)

[Vladimir Kozlov]

On Tue, 27 Jun 2023 14:40:49 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> The crash occurs because at split if during IGVN, a `SubTypeCheck` is
> created with null as input. That happens because the control path the
> `SubTypeCheck` is cloned for is dead. To fix that I propose delaying
> split if until dead paths are collapsed.
> 
> I added an assert to check a nullable first input to `SubTypeCheck`
> nodes (which should be impossible because it should be null
> checked). When I ran testing, a number of cases showed up with known
> non null values non properly marked as non null. I fixed them.

Looks reasonable.

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Marked as reviewed by kvn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14678#pullrequestreview-1501407243