RFR: 8308869: C2: use profile data in subtype checks when profile has more than one class [v5]

[Roland Westrelin]

> 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...

Roland Westrelin has updated the pull request incrementally with one additional commit since the last revision:

  whitespaces

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14375/files
  - new: https://git.openjdk.org/jdk/pull/14375/files/a2c8055c..6daa01d0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14375&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14375&range=03-04

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14375.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14375/head:pull/14375

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