RFR: 8325467: Support methods with many arguments in C2 [v31]

[Daniel Lundén]

> If a method has a large number of parameters, we currently bail out from C2 compilation.
> 
> ### Changeset
> 
> Allowing C2 compilation of methods with a large number of parameters requires fundamental changes to the register mask data structure, used in many places in C2. In particular, register masks currently have a statically determined size and cannot represent arbitrary numbers of stack slots. This is needed if we want to compile methods with arbitrary numbers of parameters. Register mask operations are present in performance-sensitive parts of C2, which further complicates changes.
> 
> Changes:
> - Add functionality to dynamically grow/extend register masks. I experimented with a number of design choices to achieve this. To keep the common case (normal number of method parameters) quick and also to avoid more intrusive changes to the current `RegMask` interface, I decided to leave the "base" statically allocated memory for masks unchanged and only use dynamically allocated memory in the rare cases where it is needed.
> - Generalize the "chunk"-logic from `PhaseChaitin::Select()` to allow arbitrary-sized chunks, and also move most of the logic into register mask methods to separate concerns and to make the `PhaseChaitin::Select()` code more readable.
> - Remove all `can_represent` checks and bailouts.
> - Performance tuning. A particularly important change is the early-exit optimization in `RegMask::overlap`, used in the performance-sensitive method `PhaseChaitin::interfere_with_live`.
> - Add a new test case `TestManyMethodArguments.java` and extend an old test `TestNestedSynchronize.java`.
> 
> ### Testing
> 
> - [GitHub Actions](https://github.com/dlunde/jdk/actions/runs/10178060450)
> - `tier1` to `tier4` (and additional Oracle-internal testing) on Windows x64, Linux x64, Linux aarch64, macOS x64, and macOS aarch64.
> - Standard performance benchmarking. No observed conclusive overall performance degradation/improvement.
> - Specific benchmarking of C2 compilation time. The changes increase C2 compilation time by, approximately and on average, 1% for methods that could also be compiled before this changeset (see the figure below). The reason for the degradation is further checks required in performance-sensitive code (in particular `PhaseChaitin::remove_bound_register_from_interfering_live_ranges`). I have tried optimizing in various ways, but changes I found that lead to improvement also lead to less readable code (and are, in my opinion, not worth it).
> 
> ![c2-regression](https:/...

Daniel Lundén has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 43 commits:

 - Merge tag 'jdk-26+16' into many-arguments-8325467+pr-updates
   
   Added tag jdk-26+16 for changeset a49856bb
 - Add vm-assert tests and improve template framework test indentation
 - Update after comments from Emanuel
 - Update after comments from Emanuel
 - Clarify comments in regmask.hpp
 - Merge remote-tracking branch 'upstream/master' into many-arguments-8325467+pr-updates
 - Address review comments (renaming on the way in a separate PR)
 - Update src/hotspot/share/opto/regmask.hpp
   
   Co-authored-by: Emanuel Peter <emanuel.peter at oracle.com>
 - Restore modified java/lang/invoke tests
 - Sort includes (new requirement)
 - ... and 33 more: https://git.openjdk.org/jdk/compare/a49856bb...84efc2db

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Changes: https://git.openjdk.org/jdk/pull/20404/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20404&range=30
  Stats: 2890 lines in 29 files changed: 2325 ins; 288 del; 277 mod
  Patch: https://git.openjdk.org/jdk/pull/20404.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20404/head:pull/20404

PR: https://git.openjdk.org/jdk/pull/20404