On Mon, 1 May 2023 20:20:51 GMT, Cesar Soares Lucas <cslu...@openjdk.org> wrote:
>> Can I please get reviews for this PR? >> >> The most common and frequent use of NonEscaping Phis merging object >> allocations is for debugging information. The two graphs below show numbers >> for Renaissance and DaCapo benchmarks - similar results are obtained for all >> other applications that I tested. >> >> With what frequency does each IR node type occurs as an allocation merge >> user? I.e., if the same node type uses a Phi N times the counter is >> incremented by N: >> >>  >> >> What are the most common users of allocation merges? I.e., if the same node >> type uses a Phi N times the counter is incremented by 1: >> >>  >> >> This PR adds support scalar replacing allocations participating in merges >> used as debug information OR as a base for field loads. I plan to create >> subsequent PRs to enable scalar replacement of merges used by other node >> types (CmpP is next on the list) subsequently. >> >> The approach I used for _rematerialization_ is pretty straightforward. It >> consists basically of the following. 1) New IR node (suggested by V. >> Kozlov), named SafePointScalarMergeNode, to represent a set of >> SafePointScalarObjectNode; 2) Each scalar replaceable input participating in >> a merge will get a SafePointScalarObjectNode like if it weren't part of a >> merge. 3) Add a new Class to support the rematerialization of SR objects >> that are part of a merge; 4) Patch HotSpot to be able to serialize and >> deserialize debug information related to allocation merges; 5) Patch C2 to >> generate unique types for SR objects participating in some allocation merges. >> >> The approach I used for _enabling the scalar replacement of some of the >> inputs of the allocation merge_ is also pretty straightforward: call >> `MemNode::split_through_phi` to, well, split AddP->Load* through the merge >> which will render the Phi useless. >> >> I tested this with JTREG tests tier 1-4 (Windows, Linux, and Mac) and didn't >> see regression. I also experimented with several applications and didn't see >> any failure. I also ran tests with "-ea -esa -Xbatch -Xcomp >> -XX:+UnlockExperimentalVMOptions -XX:-TieredCompilation -server >> -XX:+IgnoreUnrecognizedVMOptions -XX:+UnlockDiagnosticVMOptions >> -XX:+StressLCM -XX:+StressGCM -XX:+StressCCP" and didn't observe any related >> failures. > > Cesar Soares Lucas has updated the pull request with a new target base due to > a merge or a rebase. The pull request now contains 12 commits: > > - Merge remote-tracking branch 'origin/master' into > rematerialization-of-merges > - Address part of PR review 4 & fix a bug setting only_candidate > - Catching up with master > > Merge remote-tracking branch 'origin/master' into > rematerialization-of-merges > - Fix tests. Remember previous reducible Phis. > - Address PR review 3. Some comments and be able to abort compilation. > - Merge with Master > - Addressing PR review 2: refactor & reuse MacroExpand::scalar_replacement > method. > - Address PR feeedback 1: make ObjectMergeValue subclass of ObjectValue & > create new IR class to represent scalarized merges. > - Add support for SR'ing some inputs of merges used for field loads > - Fix some typos and do some small refactorings. > - ... and 2 more: https://git.openjdk.org/jdk/compare/561ec9c5...542c5ef1 It took longer than I expected, but I finished looking into debug info. A couple of minor comments first: * Please, ensure that the AllocationMergesTests.java has cases to trigger the case when SRs and NSRs meet at a merge point. I was not able to provoke it with the unit test. * diagnostic output becomes much harder to read (sample output follows). Sample output: - ordniary SR case Expression stack - @0: obj: ID=1335, only_merge_candidate=0, skip_field_assignment=0, N.Fields=4, klass: java.lang.String Fields: 0, 0, 0, nullptr ... Objects obj: ID=1335, only_merge_candidate=0, skip_field_assignment=0, N.Fields=4, klass: java.lang.String Fields: 0, 0, 0, nullptr - mixed merge case: ScopeDesc(pc=0x00000001080bc664 offset=1824): java.lang.String::substring@8 (line 2830) Locals - l0: merge: ID=1781, N.Candidates=1 ... Objects merge: ID=1781, N.Candidates=1obj: ID=1782, only_merge_candidate=1, skip_field_assignment=0, N.Fields=4, klass: java.lang.String Fields: 0, 0, 0, reg rfp [58],oop ------------- PR Comment: https://git.openjdk.org/jdk/pull/12897#issuecomment-1538801137
