RFR: 8371178: Preserve fast version of getfield and putfield in AOTCache

[Ioi Lam]

On Tue, 4 Nov 2025 17:02:21 GMT, Ashutosh Mehra <asmehra at openjdk.org> wrote:

>> src/hotspot/share/cds/aotMetaspace.cpp line 556:
>> 
>>> 554:         case ztos:
>>> 555:           new_code = Bytecodes::_fast_bgetfield;
>>> 556:           break;
>> 
>> Why is this `switch` block necessary? Is it possible for `new_code` to be different than `*bcs.bcp()`? If not, it might be easier to initialize `new_code` to `Bytecodes::_illegal` and then do the rewriting only if `new_code` has been updated.
>
>> Why is this switch block necessary? Is it possible for new_code to be different than *bcs.bcp()?
> 
> During preimage dumping all the fast bytecodes will be converted to nofast version because the CP entries are not resolved. So in the assembly phase `*bcs.bcp()` would be nofast version. If the CP entry is resolved, we can convert it to fast version. And we determine the type of the fast version using `tos_state` of the resolved field entry. So the `new_code` will be different than the `*bcs.bcp()` in the assembly phase.
> They may be same when dumping dynamic archives, but not when dumping static archive or the final AOTCache.
> Does that help?

I see. Could you add a comment? Maybe the code should be reformatted like this to make it easier to navigate?


        case ftos:  new_code = Bytecodes::_fast_fgetfield;  break;
        case dtos: new_code = Bytecodes::_fast_dgetfield; break;
        default:  ShouldNotReachHere();

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PR Review Comment: https://git.openjdk.org/jdk/pull/28121#discussion_r2491446913