RFR: 8350892: [JVMCI] Align ResolvedJavaType.getInstanceFields with Class.getDeclaredFields

[Doug Simon]

On Wed, 5 Mar 2025 12:26:12 GMT, Yudi Zheng <yzheng at openjdk.org> wrote:

>> The current order of fields returned by `ResolvedJavaType.getInstanceFields` is a) not well specified and b) different than the order of fields used almost everywhere else in HotSpot. This PR aligns the order of `getInstanceFields` with `Class.getDeclaredFields()`.
>> 
>> It also makes `ciInstanceKlass::_nonstatic_fields` use the same order which unifies how escape analysis and deoptimization treats fields across C2 and JVMCI.
>
> src/hotspot/share/ci/ciInstanceKlass.cpp line 481:
> 
>> 479:   // Now sort them by offset, ascending.
>> 480:   // (In principle, they could mix with superclass fields.)
>> 481:   fields->sort(sort_field_by_offset);
> 
> This has no effect now, i.e., the fields were sorted already?

They now have whatever sort order is given by JavaFieldStream. This happens to currently be class file declaration order but it doesn't really matter if it changes. The only requirement is that the same order is used by `get_reassigned_fields` in `deoptimization.cpp`.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/23849#discussion_r1981441818