RFR: 8319793: C2 compilation fails with "Bad graph detected in build_loop_late" after JDK-8279888 [v9]

[Roland Westrelin]

On Thu, 4 Jan 2024 16:18:16 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> Roland Westrelin has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 11 commits:
>> 
>>  - Merge branch 'master' into JDK-8319793
>>  - review
>>  - Revert "Update src/hotspot/share/opto/castnode.hpp"
>>    
>>    This reverts commit 356c91cca911ed486f9f87f3eff53ce21e1e3ec9.
>>  - Revert "Update src/hotspot/share/opto/memnode.hpp"
>>    
>>    This reverts commit bdb731ea562f314f44d327f7243ef5cf9ad40b2e.
>>  - review
>>  - Update src/hotspot/share/opto/memnode.hpp
>>    
>>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>>  - Update src/hotspot/share/opto/castnode.hpp
>>    
>>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>>  - Update src/hotspot/share/opto/castnode.cpp
>>    
>>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>>  - Update src/hotspot/share/opto/ifnode.cpp
>>    
>>    Co-authored-by: Christian Hagedorn <christian.hagedorn at oracle.com>
>>  - Merge branch 'master' into JDK-8319793
>>  - ... and 1 more: https://git.openjdk.org/jdk/compare/15519285...dbe3c4c1
>
> src/hotspot/share/opto/loopopts.cpp line 361:
> 
>> 359:     return; // Let IGVN transformation change control dependence.
>> 360:   }
>> 361: 
> 
> Why it ok to remove this bailout?

It's:
"IfNode::dominated_by() and PhaseIdealLoop::dominated_by() have
logic to prevent this: nodes that are control dependent on a range
check or predicate are not allowed to float."
that I mentioned in the fix description. It's the way array access nodes are currently prevented from floating above the range checks they depend on. It's flawed, replaced by pinning of the array access nodes in the patch. So this logic is no longer useful.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16886#discussion_r1442687996