RFR: 8339112: Move JVM Klass flags out of AccessFlags [v2]

[Dean Long]

On Thu, 29 Aug 2024 18:50:42 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> Move JVM implementation access flags that are not specified by the classfile format into Klass so we can shrink AccessFlags to u2 in a future change.
>> 
>> Tested with tier1-7.
>> 
>> NOTE: there are arm, ppc and s390 changes to this that are just a guess.  Also, graal changes.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add in graal flags and a comment.

src/hotspot/share/ci/ciKlass.cpp line 231:

> 229: // ------------------------------------------------------------------
> 230: // ciKlass::misc_flags
> 231: jint ciKlass::misc_flags() {

Suggestion:

u1 ciKlass::misc_flags() {

I think this should match what misc_flags() returns.  Ideally, I think it should be a typedef like KlassFlags_t so we don't have to make a lot of changes if grows to u2.

src/hotspot/share/ci/ciKlass.hpp line 125:

> 123: 
> 124:   // Fetch Klass::misc_flags.
> 125:   jint                   misc_flags();

Suggestion:

  KlassFlags_t           misc_flags();

src/hotspot/share/oops/klass.hpp line 436:

> 434: #endif
> 435:   static ByteSize bitmap_offset()                { return byte_offset_of(Klass, _bitmap); }
> 436:   static ByteSize misc_flags_offset()            { return byte_offset_of(Klass, _misc_flags); }

Suggestion:

  static ByteSize misc_flags_offset()            { return byte_offset_of(Klass, _misc_flags._flags); }

src/hotspot/share/oops/klassFlags.hpp line 56:

> 54:   // These flags are write-once before the class is published and then read-only
> 55:   // so don't require atomic updates.
> 56:   u1 _flags;

Suggestion:

  typedef u1 KlassFlags_t;
  KlassFlags_t _flags;

Can we have a typedef so C++ code that doesn't care about the size doesn't need to change if we later make it u2 or u4?

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

PR Review Comment: https://git.openjdk.org/jdk/pull/20719#discussion_r1737291678
PR Review Comment: https://git.openjdk.org/jdk/pull/20719#discussion_r1737299082
PR Review Comment: https://git.openjdk.org/jdk/pull/20719#discussion_r1737303285
PR Review Comment: https://git.openjdk.org/jdk/pull/20719#discussion_r1737294456