Bug ID: JDK-8316991 Reduce nullable allocation merges

JDK-8316991 : Reduce nullable allocation merges

Type: Enhancement
Component: hotspot
Sub-Component: compiler
Affected Version: 22,23

Priority: P4
Status: Resolved
Resolution: Fixed

Submitted: 2023-09-26
Updated: 2024-09-06
Resolved: 2024-04-08

Versions (Unresolved/Resolved/Fixed)

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Resolved: Release in which this issue/RFE has been resolved.
Fixed : Release in which this issue/RFE has been fixed. The release containing this fix may be available for download as an Early Access Release or a General Availability Release.

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JDK 23
23 b18Fixed

Related Reports

Relates :	JDK-8330565 - C2: Multiple crashes with CTW after JDK-8316991
Relates :	JDK-8330277 - Reduce allocation merges is spewing C2 dumps in debug builds
Relates :	JDK-8289943 - Simplify some object allocation merges
Relates :	JDK-8287061 - Support for rematerializing scalar replaced objects participating in allocation merges
Relates :	JDK-8315003 - [lworld] Implement full support for JDK-8287061 and JDK-8316991
Relates :	JDK-8331194 - NPE in ArrayCreationTree.java with -XX:-UseCompressedOops
Relates :	JDK-8335220 - C2: Missing check for Opaque4 node in EscapeAnalysis
Relates :	JDK-8330247 - C2: CTW fail with assert(adr_t->is_known_instance_field()) failed: instance required
Relates :	JDK-8330795 - C2: assert((uint)type <= T_CONFLICT && _zero_type[type] != nullptr) failed: bad type with -XX:-UseCompressedClassPointers
Relates :	JDK-8331736 - C2: Live Node limit exceeded limit after JDK-8316991
Relates :	JDK-8330419 - Unused code in ConnectionGraph::specialize_castpp
Relates :	JDK-8330853 - Add missing checks for ConnectionGraph::can_reduce_cmp() call
Relates :	JDK-8330213 - RISC-V: C2: assert(false) failed: bad AD file after JDK-8316991

Description

Follow up from JDK-8287061.

Many, if not most, allocation merges (Phis) are nullable because they join object allocations with "NULL", or objects returned from method calls, etc.

This Sub-task is to improve Reduce Allocation Merge implementation so that it can reduce at least some of these allocation merges.

Comments

I converted this to a separate RFE independent of JDK-8289943 to avoid the indirection when following links from the related bugs/RFEs.

22-08-2024

Changeset: a887fd21 Author: Cesar Soares Lucas <cslucas@openjdk.org> Committer: Vladimir Kozlov <kvn@openjdk.org> Date: 2024-04-08 23:13:38 +0000 URL: https://git.openjdk.org/jdk/commit/a887fd2144ce067844f18a514afb5078255601ff

08-04-2024

A pull request was submitted for review. URL: https://git.openjdk.org/jdk/pull/15825 Date: 2023-09-19 18:54:34 +0000

26-09-2023