Integrated: JDK-8287061: Support for rematerializing scalar replaced objects participating in allocation merges
Cesar Soares Lucas
cslucas at openjdk.org
Mon Jul 17 23:05:29 UTC 2023
On Tue, 7 Mar 2023 01:40:48 GMT, Cesar Soares Lucas <cslucas at openjdk.org> wrote:
> Can I please get reviews for this PR?
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> 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.
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> 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:
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> 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:
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> 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.
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> 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.
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> 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.
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> 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.
This pull request has now been integrated.
Changeset: a53345ad
Author: Cesar Soares Lucas <cslucas at openjdk.org>
Committer: Vladimir Kozlov <kvn at openjdk.org>
URL: https://git.openjdk.org/jdk/commit/a53345ad03e07ab2a990721a506ebc25eed0f7c9
Stats: 2733 lines in 26 files changed: 2485 ins; 108 del; 140 mod
8287061: Support for rematerializing scalar replaced objects participating in allocation merges
Reviewed-by: kvn, vlivanov
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PR: https://git.openjdk.org/jdk/pull/12897
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