RFR: 8363996: Obsolete UseCompressedClassPointers [v4]

[Thomas Stuefe]

On Mon, 8 Dec 2025 13:26:59 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

>> Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update src/hotspot/cpu/aarch64/c1_LIRAssembler_aarch64.cpp
>>   
>>   Co-authored-by: Andrew Haley <aph-open at littlepinkcloud.com>
>
> src/hotspot/share/oops/oop.inline.hpp line 104:
> 
>> 102:       return CompressedKlassPointers::decode_not_null(_metadata._compressed_klass);
>> 103:     default:
>> 104:       return _metadata._klass;
> 
> Suggestion:
> 
>       ShouldNotReachHere();

Fixed

> src/hotspot/share/oops/oop.inline.hpp line 115:
> 
>> 113:       return CompressedKlassPointers::decode(_metadata._compressed_klass);
>> 114:     default:
>> 115:       return _metadata._klass;
> 
> Suggestion:
> 
>       ShouldNotReachHere();

Fixed

> src/hotspot/share/oops/oop.inline.hpp line 128:
> 
>> 126:     }
>> 127:     default:
>> 128:       return AtomicAccess::load_acquire(&_metadata._klass);
> 
> Suggestion:
> 
>       ShouldNotReachHere();

Fixed

> src/hotspot/share/oops/oop.inline.hpp line 139:
> 
>> 137:       return CompressedKlassPointers::decode_without_asserts(_metadata._compressed_klass);
>> 138:     default:
>> 139:       return _metadata._klass;
> 
> klass_mode() is either `Compact` or `Compressed`
> Should be changed to:
> Suggestion:
> 
>       ShouldNotReachHere();

Fixed

> src/hotspot/share/oops/oop.inline.hpp line 157:
> 
>> 155:   assert(Universe::is_bootstrapping() || (k != nullptr && k->is_klass()), "incorrect Klass");
>> 156:   assert(!UseCompactObjectHeaders, "don't set Klass* with compact headers");
>> 157:   _metadata._compressed_klass = CompressedKlassPointers::encode_not_null(k);
> 
> We might have to reconsider if we need to maintain the`union _metadata`

Right you are. We only should need narrowKlass now, even on 32-bit.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/28366#discussion_r2782264507
PR Review Comment: https://git.openjdk.org/jdk/pull/28366#discussion_r2782265537
PR Review Comment: https://git.openjdk.org/jdk/pull/28366#discussion_r2782263749
PR Review Comment: https://git.openjdk.org/jdk/pull/28366#discussion_r2782263330
PR Review Comment: https://git.openjdk.org/jdk/pull/28366#discussion_r2782039682