Integrated: 8308869: C2: use profile data in subtype checks when profile has more than one class

[Roland Westrelin]

On Thu, 8 Jun 2023 11:23:14 GMT, Roland Westrelin <roland at openjdk.org> wrote:

> In this simple micro benchmark:
> 
> https://github.com/franz1981/java-puzzles/blob/main/src/main/java/red/hat/puzzles/polymorphism/RequireNonNullCheckcastScalability.java#L70
> 
> Performance drops sharply with polluted profile:
> 
> 
> Benchmark                                         (typePollution)   Mode  Cnt     Score    Error   Units
> RequireNonNullCheckcastScalability.isDuplicated1            false  thrpt   10  1453.372 ± 24.919  ops/us
> 
> 
> to:
> 
> 
> Benchmark                                         (typePollution)   Mode  Cnt   Score   Error   Units
> RequireNonNullCheckcastScalability.isDuplicated1             true  thrpt   10  28.579 ± 2.280  ops/us
> 
> 
> The test has 2 type checks to 2 different interfaces so caching with
> `secondary_super_cache` doesn't help.
> 
> The micro-benchmark only uses 2 different concrete classes
> (`DuplicatedContext` and `NonDuplicatedContext`) and they are recorded
> in profile data at the type checks. But c2 only take advantage of
> profile data at type checks if they report a single class.
> 
> What I propose is that the full blown type check expanded in
> `Phase::gen_subtype_check()` takes advantage of profile data. So in
> the case of the micro benchmark, before checking the
> `secondary_super_cache`, generated code checks whether the object
> being type checked is a `DuplicatedContext` or a
> `NonDuplicatedContext`.
> 
> This works fairly well on this micro benchmark:
> 
> 
> Benchmark                                         (typePollution)   Mode  Cnt    Score    Error   Units
> RequireNonNullCheckcastScalability.isDuplicated1             true  thrpt   10  871.224 ± 20.750  ops/us
> 
> 
> It also scales much better if there are multiple threads running the
> same test (`secondary_super_cache` doesn't scale well: see
> JDK-8180450).
> 
> Now if the micro-benchmark is changed according to the comment:
> 
> https://github.com/franz1981/java-puzzles/blob/d2d60af3d0dfe7a2567807395138edcb1d1c24f5/src/main/java/red/hat/puzzles/polymorphism/RequireNonNullCheckcastScalability.java#L62
> 
> so the type check hits in the `secondary_super_cache`, the current
> code performs much better:
> 
> 
> Benchmark                                         (typePollution)   Mode  Cnt    Score    Error   Units
> RequireNonNullCheckcastScalability.isDuplicated1             true  thrpt   10  871.224 ± 20.750  ops/us
> 
> 
> but leveraging profiling as explained above performs even better:
> 
> 
> Benchmark                                         (typePollution)   Mode  Cnt     Score    Error   Units
> RequireNonNullCheckcastScalability.isDuplic...

This pull request has now been integrated.

Changeset: dac17279
Author:    Roland Westrelin <roland at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/dac1727956cf9edeae1dad677f3f9ae87882a6b9
Stats:     1148 lines in 36 files changed: 684 ins; 329 del; 135 mod

8308869: C2: use profile data in subtype checks when profile has more than one class

Co-authored-by: Fei Yang <fyang at openjdk.org>
Reviewed-by: vlivanov, thartmann

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

PR: https://git.openjdk.org/jdk/pull/14375