RFR: 8371964: C2 compilation asserts with "Unexpected load/store size" [v2]

[Vladimir Ivanov]

On Thu, 20 Nov 2025 12:58:55 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> Done, running `compiler/arraycopy/TestArrayCopyDisjoint.java` with `-XX:+UnlockDiagnosticVMOptions -XX:-TieredCompilation -XX:+StressArrayCopyMacroNode -XX:+StressLCM -XX:+StressGCM -XX:+StressIGVN -XX:+StressCCP -XX:+StressMacroExpansion -XX:+StressMethodHandleLinkerInlining -XX:+StressCompiledExceptionHandlers -XX:VerifyConstraintCasts=1 -XX:+StressLoopPeeling` encounters this issue. Do you think it is necessary to add a separate case for that test, then?
>
> Thanks for the update! If it's a short running test/config, then I think it would be good to have this extra config to cover the changes of this patch.

Is it truly specific to post-loop opts phase? Isn't it yet another paradoxical IR shape occurring in effectively dead code?

In the longer term, it would be good to ensure such effectively dead nodes eventually go away. Or, better, eagerly trigger their elimination. Otherwise, it could cause issues later in compilation process unless the problematic conditions are explicitly handled everywhere (e.g., during matching or code generation for `vmask_gen_imm` on x64 and AArch64).

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PR Review Comment: https://git.openjdk.org/jdk/pull/28410#discussion_r2547888182