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

[Aleksey Shipilev]

On Tue, 29 Jun 2021 17:07:23 GMT, Vladimir Kozlov <kvn 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`
>
> @shipilev can it be related to  [8268884](https://bugs.openjdk.java.net/browse/JDK-8268884)?

@vnkozlov More precisely, here are the types that `join_speculative` encounters on the failing path:


STDOUT:
arg_type: byte[int:>=0]:exact * (speculative=byte[int:>=0]:NotNull:exact *)
sig_type: java/io/Serializable *
narrowed_arg_type: java/lang/Object:AnyNull *,iid=top

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