[lworld] RFR: 8352647: [lworld] Remove larval InlineTypeNode in Unsafe intrinsics

[Quan Anh Mai]

On Fri, 28 Mar 2025 08:42:52 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> @TobiHartmann
>> 
>>> But this will not prevent users from passing larval objects created via makePrivateBuffer to other methods, right? I.e., we still have the issues described in [JDK-8239003](https://bugs.openjdk.org/browse/JDK-8239003) (and linked issues).
>> 
>> My stance on this matter is that we should simply disallow passing larval objects except to `Unsafe::putXXX` and `Unsafe::finishPrivateBuffer`. What do you think?
>
> Hi @merykitty ,
> For attached test case I am seeing crash at state merge point b/w larval and non-larval value
>  
> [unsafe_access.txt](https://github.com/user-attachments/files/19501609/unsafe_access.txt)
> 
> 
> CPROMPT>javac --enable-preview -source 25 --add-exports=java.base/jdk.internal.misc=ALL-UNNAMED unsafe_access.java
> Note: unsafe_access.java uses preview features of Java SE 25.
> Note: Recompile with -Xlint:preview for details.
> CPROMPT>
> CPROMPT>java -XX:-PauseAtStartup --enable-preview --add-exports=java.base/jdk.internal.misc=ALL-UNNAMED -cp . unsafe_access
> #
> # A fatal error has been detected by the Java Runtime Environment:
> #
> #  Internal Error (/home/jatinbha/sandboxes/lworld/src/hotspot/share/opto/parse1.cpp:1790), pid=2453805, tid=2453825
> #  assert(gvn().type(n)->is_zero_type()) failed: Should have been scalarized
> #
> # JRE version: OpenJDK Runtime Environment (25.0) (slowdebug build 25-internal-adhoc.root.lworld)
> # Java VM: OpenJDK 64-Bit Server VM (slowdebug 25-internal-adhoc.root.lworld, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, linux-amd64)
> # Problematic frame:
> # V  [libjvm.so+0x178efa5]  Parse::merge_common(Parse::Block*, int)+0x49f
> #
> # Core dump will be written. Default location: Core dumps may be processed with "/usr/share/apport/apport -p%p -s%s -c%c -d%d -P%P -u%u -g%g -- %E" (or dumping to /home/jatinbha/code/java/valhalla/core.2453805)
> #
> # An error report file with more information is saved as:
> # /home/jatinbha/code/java/valhalla/hs_err_pid2453805.log
> 10001399990
> #
> # Compiler replay data is saved as:
> # /home/jatinbha/code/java/valhalla/replay_pid2453805.log
> #
> # If you would like to submit a bug report, please visit:
> #   https://bugreport.java.com/bugreport/crash.jsp
> #
> Aborted (core dumped)

@jatin-bhateja Merging a larval object and a non-larval object is undefined behaviour, and crashing should be an acceptable outcome then. There are issues with merges of larval objects, though, for example:

    MyValue v = UNSAFE.makePrivateBuffer(v0);
    for (int i = 0; i < 100; i++) {}
    return UNSAFE.finishPrivateBuffer(v);

But generally, the situation of merging larval objects are messy not just with larval objects created by `Unsafe` and I want to defer the fix to after #1405.

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PR Comment: https://git.openjdk.org/valhalla/pull/1406#issuecomment-2761918786