RFR: 8339733: C2: some nodes can have incorrect control after do_range_check() [v4]

[Tobias Hartmann]

On Wed, 11 Sep 2024 11:21:41 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> PhaseIdealLoop::do_range_check() sets the control of the new pre and
>> main limits to be the entry control of the pre loop but it eliminates
>> all conditions whose parameters are invariant in the main loop. Most
>> of the time they are also invariant in the pre loop but that's not
>> guaranteed. It does happen sometimes that those parameters are pinned
>> in the pre loop. In that case, PhaseIdealLoop::do_range_check() sets
>> wrong controls.
>> 
>> This doesn't cause any issue today AFAICT.
>> 
>> Also, this seems to be a typo in PhaseIdealLoop::insert_pre_post_loops():
>> 
>> 
>> pre_head->in(0)
>> 
>> 
>> is `pre_head`. I fixed that one too.
>
> Roland Westrelin has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Update src/hotspot/share/opto/loopTransform.cpp
>    
>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>  - Update src/hotspot/share/opto/loopTransform.cpp
>    
>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>

Looks good to me too.

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Marked as reviewed by thartmann (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20908#pullrequestreview-2299335041