RFR: 8354887: Preserve runtime blobs in AOT code cache [v6]

[Andrew Dinn]

On Tue, 13 May 2025 18:03:09 GMT, Ashutosh Mehra <asmehra at openjdk.org> wrote:

>> [8350209](https://bugs.openjdk.org/browse/JDK-8350209) introduced the framework for storing code in aot code cache and used it for caching i2c/c2i adapters.
>> This PR extends the `AOTCodeCache` infrastructure and stores various runtime blobs (shared blobs, C1 and C2 runtime blobs) in the AOT code cache. It adds a new diagnostic flag `AOTStubCaching` to enable/disable the caching of these blobs.
>> `AOTCodeFlags.java` test is extended to cover `AOTStubCaching`.
>
> Ashutosh Mehra has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 18 commits:
> 
>  - Merge branch 'master' into preserve-runtime-blobs-master
>  - Address Vladimir's comments
>    
>    Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
>  - Update test to make it more resilient
>    
>    Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
>  - Remove more unused code
>    
>    Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
>  - Fix whitespace issue. Remove unused code.
>    
>    Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
>  - Add test for using AOTCodeCache with different CompressedOops
>    configuration
>    
>    Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
>  - Add check for compressed oops base address; minor refacotring
>    
>    Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
>  - Merge branch 'master' into preserve-runtime-blobs-master
>  - Address Vladimir's comments
>    
>    Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
>  - Remove irrelevant comment
>    
>    Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
>  - ... and 8 more: https://git.openjdk.org/jdk/compare/d1543429...5d7c3aa0

src/hotspot/cpu/aarch64/sharedRuntime_aarch64.cpp line 2188:

> 2186: #endif
> 2187:   const char* name = SharedRuntime::stub_name(SharedStubId::deopt_id);
> 2188:   CodeBlob* blob = AOTCodeCache::load_code_blob(AOTCodeEntry::SharedBlob, (uint)SharedStubId::deopt_id, name);

For most shared blobs we have a single entry at offset 0. However, for the deopt blob we have 3 (or 5) extra entry points which are embedded in the deopt blob as field values. Saving and restoring the blob internal state removes the need to pass a count and array of entry offsets into load_code_blob and store_code_blob at this point.
That makes we wonder if we need to do the same with AdapterBlob. If we embedded the offsets that are currently stored in AdapterHandlerEntry into AdapterBlob then we could also avoid having to explicitly pass the count and array of offsets at AOT load/store for adapters. The getters in AdapterHandlerEntry could fetch them indirectly or else the entry could cache them locally when it is initialized depending on whether we care about a memory indirection. Maybe this would make things more uniform?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25019#discussion_r2091438273