On Wed, 26 Apr 2023 17:28:53 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 incrementally with one > additional commit since the last revision: > > Address part of PR review 4 & fix a bug setting only_candidate I have an update to this PR to make it possible to scalar replace allocations when the Phi is used in a CmpP (not for all cases). Is there any objection to me pushing these changes? I.e., will it complicate any ongoing review? ------------- PR Comment: https://git.openjdk.org/jdk/pull/12897#issuecomment-1530047937
