RFR: 8361699: C2: assert(can_reduce_phi(n->as_Phi())) failed: Sanity: previous reducible Phi is no longer reducible before SUT [v2]

[Tobias Hartmann]

On Wed, 10 Sep 2025 18:39:06 GMT, Cesar Soares Lucas <cslucas at openjdk.org> wrote:

>> Please, review this patch to fix issue that may occur when reducing allocation merge.
>> 
>> As the assert message describe, the problem is a `Phi` considered reducible during one invocation of  `adjust_scalar_replaceable_state` turned out to be later non-reducible. This situation can happen if a subsequent invocation of the same method causes all inputs to the phi to be NSR; therefore there is no point in reducing the Phi. It can also happen during the propagation of NSR state done by `find_scalar_replaceable_allocs`. 
>> 
>> The change in `revisit_reducible_phi_status` is just a clean-up.
>> The real fix is in `find_scalar_replaceable_allocs`.
>> 
>> Tested on Linux x64/Aarch64 release/fastdebug with JTREG tier1-3.
>
> Cesar Soares Lucas has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Revert clean-up in EA. Make catch statements more specific in test case.

src/hotspot/share/opto/escape.cpp line 3135:

> 3133:           Node* phi = use->ideal_node();
> 3134:           if (phi->Opcode() == Op_Phi && reducible_merges.member(phi)) {
> 3135:             if (!can_reduce_phi(phi->as_Phi())) {

Drive-by comment: I think the ifs should be merged

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PR Review Comment: https://git.openjdk.org/jdk/pull/27063#discussion_r2339804735