8266845: Shenandoah: Simplify SBS::load_reference_barrier implementation

[zhengyu123]

Early return on null obj simplifies implementation and makes code more readable.

Test:

• hotspot_gc_shenandoah

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Issue

• JDK-8266845: Shenandoah: Simplify SBS::load_reference_barrier implementation

Reviewers

• Aleksey Shipilev (@shipilev - Reviewer) ⚠️ Review applies to 4a70d93

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jdk pull/3956/head:pull/3956
$ git checkout pull/3956

Update a local copy of the PR:
$ git checkout pull/3956
$ git pull https://git.openjdk.java.net/jdk pull/3956/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 3956

View PR using the GUI difftool:
$ git pr show -t 3956

Using diff file

Download this PR as a diff file:
https://git.openjdk.java.net/jdk/pull/3956.diff

[bridgekeeper]

👋 Welcome back zgu! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

@zhengyu123 The following labels will be automatically applied to this pull request:

• hotspot-gc
• shenandoah

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing lists. If you would like to change these labels, use the /label pull request command.

[mlbridge]

Webrevs

• 02: Full - Incremental (900185fb)
• 01: Full - Incremental (4a70d935)
• 00: Full (8ed81d6c)

[shipilev]

Provisionally approving, modulo the nit.

[openjdk]

@zhengyu123 This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8266845: Shenandoah: Simplify SBS::load_reference_barrier implementation

Reviewed-by: shade

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 13 new commits pushed to the master branch:

• 0344e75: 8266794: Remove dead code notify_allocation_jvmti_allocation_event
• 9e6e222: 8266892: avoid maybe-uninitialized gcc warnings on linux s390x
• 6575566: 8266787: Potential overflow of pointer arithmetic in G1ArchiveAllocator
• 8468001: 8263452: Javac slow compilation due to algorithmic complexity
• 67cb22a: 8266601: Fix bugs in AddLNode::Ideal transformations
• 18e9d28: 8266676: G1: Remove dead code init_node_id_to_index_map()
• 0e7bdae: 8265062: Remove duplication constant MaxTextureSize
• 10a049e: 8265956: JVM crashes when matching LShiftVB Node
• 9713152: 8262092: vmTestbase/nsk/jvmti/scenarios/hotswap/HS102/hs102t001/TestDescription.java SIGSEGV in memmove_ssse3
• 23446f1: 8265128: [REDO] Optimize Vector API slice and unslice operations
• ... and 3 more: https://git.openjdk.java.net/jdk/compare/f78440ad438bca2a8929475fbecfbd3c920d48df...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[zhengyu123]

/integrate

[openjdk]

@zhengyu123 Since your change was applied there have been 44 commits pushed to the master branch:

• 7433821: 8250658: Performance of ClipFlatOval Renderperf test is very low
• 4727187: 8266567: Fix javadoc tag references in sun.management.jmxremote.ConnectorBootstrap
• 11759bf: 8266798: C1: More types of instruction can also apply LoopInvariantCodeMotion
• dcf250d: 8233378: CHT: Fast reset
• f3b510b: 8266923: [JVMCI] expose StackOverflow::_stack_overflow_limit to JVMCI
• 548899d: 8266189: Remove C1 "IfInstanceOf" instruction
• b46086d: 8266874: Clean up C1 canonicalizer for TableSwitch/LookupSwitch
• 97367c0: 8266808: Search label still uses old search field id
• 06d7602: 8261158: JVMState should not be shared between SafePointNodes
• 476994a: 8266531: ZAddress::address() should be removed from SA
• ... and 34 more: https://git.openjdk.java.net/jdk/compare/f78440ad438bca2a8929475fbecfbd3c920d48df...master

Your commit was automatically rebased without conflicts.

Pushed as commit 69daedf.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.