RFR: 8281429: PhiNode::Value() is too conservative for tripcount of CountedLoop [v4]

[Christian Hagedorn]

On Mon, 28 Mar 2022 07:29:20 GMT, Roland Westrelin <roland at openjdk.org> wrote:

>> The type for the iv phi of a counted loop is computed from the types
>> of the phi on loop entry and the type of the limit from the exit
>> test. Because the exit test is applied to the iv after increment, the
>> type of the iv phi is at least one less than the limit (for a positive
>> stride, one more for a negative stride).
>> 
>> Also, for a stride whose absolute value is not 1 and constant init and
>> limit values, it's possible to compute accurately the iv phi type.
>> 
>> This change caused a few failures and I had to make a few adjustments
>> to loop opts code as well.
>
> Roland Westrelin has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 13 additional commits since the last revision:
> 
>  - test fix
>  - more test
>  - test & fix
>  - other fix
>  - Merge branch 'master' into JDK-8281429
>  - exp
>  - review
>  - Merge branch 'master' into JDK-8281429
>  - Update src/hotspot/share/opto/cfgnode.cpp
>    
>    Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
>  - Update src/hotspot/share/opto/cfgnode.cpp
>    
>    Co-authored-by: Tobias Hartmann <tobias.hartmann at oracle.com>
>  - ... and 3 more: https://git.openjdk.java.net/jdk/compare/75d84a25...3a087b2c

src/hotspot/share/opto/loopnode.cpp line 846:

> 844:   }
> 845: 
> 846:   // May not have gone thru igvn yet so don't use _igvn.type(phi) (PhaseIdealLoop::is_counted_loop() sets the iv phi's type)

Comment seems to be outdated as we are not querying the type of the phi anymore. Can you update it?

test/hotspot/jtreg/compiler/c2/irTests/TestSkeletonPredicates.java line 33:

> 31:  * @test
> 32:  * @bug 8282592
> 33:  * @summary C2: assert(false) failed: graph should be schedulable

Are the changes to this file intended? They seem to be unrelated.

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PR: https://git.openjdk.java.net/jdk/pull/7823