[jdk17] RFR: 8269285: Crash/miscompile in CallGenerator::for_method_handle_inline after JDK-8191998

[Vladimir Kozlov]

On Tue, 29 Jun 2021 09:01:23 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> See the bug report for more details.
> 
> I believe the [JDK-8191998](https://bugs.openjdk.java.net/browse/JDK-8191998) change introduced a slight regression, where the speculative type join may empty the type. It would then crash on assert in `fastdebug` builds, or miscompile the null-check to `true` in `release` bits. New test captures both failure modes.
> 
> This is not a recent regression, but a regression nevertheless, so I would like to have that fix in JDK 17. Please review carefully, or speak up if you want to move it to JDK 18+ and then backport later.
> 
> Additional testing:
>  - [x] New test fails without the patch, passes with it
>  - [x] Linux x86_64 `fastdebug` `tier1`

About joining with Interface type. Returning `Object:AnyNull` is normal answer from C2 for Interfaces. We can't handle them currently and it is not the goal of this patch.

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PR: https://git.openjdk.java.net/jdk17/pull/169