RFR: 8361702: C2: assert(is_dominator(compute_early_ctrl(limit, limit_ctrl), pre_end)) failed: node pinned on loop exit test? [v2]

[Christian Hagedorn]

On Thu, 24 Jul 2025 08:41:52 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> A node in a pre loop only has uses out of the loop dominated by the
>> loop exit. `PhaseIdealLoop::try_sink_out_of_loop()` sets its control
>> to the loop exit projection. A range check in the main loop has this
>> node as input (through a chain of some other nodes). Range check
>> elimination needs to update the exit condition of the pre loop with an
>> expression that depends on the node pinned on its exit: that's
>> impossible and the assert fires. This is a variant of 8314024 (this
>> one was for a node with uses out of the pre loop on multiple paths). I
>> propose the same fix: leave the node with control in the pre loop in
>> this case.
>
> Roland Westrelin has updated the pull request incrementally with four additional commits since the last revision:
> 
>  - Update test/hotspot/jtreg/compiler/rangechecks/TestSunkRangeFromPreLoopRCE3.java
>    
>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>  - Update test/hotspot/jtreg/compiler/rangechecks/TestSunkRangeFromPreLoopRCE2.java
>    
>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>  - Update src/hotspot/share/opto/loopopts.cpp
>    
>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>  - Update test/hotspot/jtreg/compiler/rangechecks/TestSunkRangeFromPreLoopRCE2.java
>    
>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>

Thanks for the update, testing looked good!

src/hotspot/share/opto/loopopts.cpp line 1926:

> 1924: }
> 1925: 
> 1926:  // Sinking a node from a pre loop to its main loop pins the node between the pre and main loops. If that node is input

Suggestion:

// Sinking a node from a pre loop to its main loop pins the node between the pre and main loops. If that node is input

-------------

Marked as reviewed by chagedorn (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26424#pullrequestreview-3055490801
PR Review Comment: https://git.openjdk.org/jdk/pull/26424#discussion_r2231144292