On Sat, 25 May 2024 06:48:26 GMT, Ioi Lam <ik...@openjdk.org> wrote: >> ### Overview >> >> This PR archives `CONSTANT_FieldRef` entries in the _resolved_ state when >> it's safe to do so. >> >> I.e., when a `CONSTANT_FieldRef` constant pool entry in class `A` refers to >> a *non-static* field `B.F`, >> - `B` is the same class as `A`; or >> - `B` is a supertype of `A`; or >> - `B` is one of the >> [vmClasses](https://github.com/openjdk/jdk/blob/3d4185a9ce482cc655a4c67f39cb2682b02ae4fe/src/hotspot/share/classfile/vmClasses.hpp), >> and `A` is loaded by the boot class loader. >> >> Under these conditions, it's guaranteed that whenever `A` tries to use this >> entry at runtime, `B` is guaranteed to have already been resolved in A's >> system dictionary, to the same value as resolved during dump time. >> >> Therefore, we can safely archive the `ResolvedFieldEntry` in class `A` that >> refers to `B.F`. >> >> (Note that we do not archive the `CONSTANT_FieldRef` entries for static >> fields, as the resolution of such entries can lead to class initialization >> at runtime. We plan to handle them in a future RFE.) >> >> ### Static CDS Archive >> >> This feature is implemented in three steps for static CDS archive dump: >> >> 1. At the end of the training run, `ClassListWriter` iterates over all >> loaded classes and writes the indices of their resolved `Class` and >> `FieldRef` constant pool entries into the classlist file, with the `@cp` >> prefix. E.g., the following means that the constant pool entries at indices >> 2, 19 and 106 were resolved during the training run: >> >> @cp java/util/Objects 2 19 106 >> >> 2. When creating the static CDS archive from the classlist file, >> `ClassListParser` processes the `@cp` entries and resolves all the indicated >> entries. >> >> 3. Inside the `ArchiveBuilder::make_klasses_shareable()` function, we >> iterate over all entries in all archived `ConstantPools`. When we see a >> _resolved_ entry that does not satisfy the safety requirements as stated in >> _Overview_, we revert it back to the unresolved state. >> >> ### Dynamic CDS Archive >> >> When dumping the dynamic CDS archive, `ClassListWriter` and >> `ClassListParser` are not used, so steps 1 and 2 are skipped. We only >> perform step 3 when the archive is being written. >> >> ### Limitations >> >> - For safety, we limit this optimization to only classes loaded by the boot, >> platform, and app class loaders. This may be relaxed in the future. >> - We archive only the constant pool entries that are actually resolved >> during the training run. We don't speculatively resolve other entries, as >> doing so may cause C2 to... > > Ioi Lam has updated the pull request with a new target base due to a merge or > a rebase. The incremental webrev excludes the unrelated changes brought in by > the merge/rebase. The pull request contains five additional commits since the > last revision: > > - Fixed typo in previous commit > - Merge branch 'master' into 8293980-resolve-fields-at-dumptime > - @matias9927 comments - moved > remove_resolved_field_entries_if_non_deterministic() to cpCache > - Merge branch 'master' into 8293980-resolve-fields-at-dumptime > - 8293980: Resolve CONSTANT_FieldRef at CDS dump time
Changes look good, thanks! ------------- Marked as reviewed by matsaave (Reviewer). PR Review: https://git.openjdk.org/jdk/pull/19355#pullrequestreview-2083038736
