8256883: C2: Add a RegMask iterator

[cl4es]

By implementing a simple RegMaskIterator we can speed this up and possibly make the code a bit clearer by doing so.

As a data point, this reduce the C2Compiler::initialize overhead from 8.82M instructions to 8.58M instructions, from the improvement in PhaseChaitin::post_allocate_copy_removal (~16k insns/compilation). The gain varies with type of compilation, so on the naive tests in SimpleRepeatCompilation it's in the noise (~2k insns/compilation on `trivialMath, for example).

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Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
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Testing

	Linux aarch64	Linux arm	Linux ppc64le	Linux s390x	Linux x64	Linux x86	Windows x64	macOS x64
Build	✔️ (1/1 passed)	✔️ (1/1 passed)	✔️ (1/1 passed)	✔️ (1/1 passed)	✔️ (6/6 passed)	✔️ (2/2 passed)	✔️ (2/2 passed)	✔️ (2/2 passed)
Test (tier1)					✔️ (9/9 passed)	✔️ (9/9 passed)	✔️ (9/9 passed)	✔️ (9/9 passed)

Issue

• JDK-8256883: C2: Add a RegMask iterator

Reviewers

• Vladimir Kozlov (@vnkozlov - Reviewer) ⚠️ Review applies to b928fcc
• Per Liden (@pliden - Reviewer)
• Erik Österlund (@fisk - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jdk pull/1397/head:pull/1397
$ git checkout pull/1397

[bridgekeeper]

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[openjdk]

@cl4es The following label will be automatically applied to this pull request:

• hotspot-compiler

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[mlbridge]

Webrevs

• 03: Full - Incremental (f259dd3)
• 02: Full - Incremental (b928fcc)
• 01: Full - Incremental (b5345e9)
• 00: Full (4192cff)

[vnkozlov]

There are 2 places in ZGC code (x86 and aarch64) which could use new iterator too:
https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/gc/z/zBarrierSetAssembler_x86.cpp#L482

[cl4es]

/label remove hotspot
/label add hotspot-gc
/label add hotspot-compiler

[openjdk]

@cl4es
The hotspot label was successfully removed.

[openjdk]

@cl4es
The hotspot-gc label was successfully added.

[openjdk]

@cl4es
The hotspot-compiler label was successfully added.

[vnkozlov]

Good.

[openjdk]

@cl4es 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:

8256883: C2: Add a RegMask iterator

Reviewed-by: kvn, pliden, eosterlund

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 29 new commits pushed to the master branch:

• 9e4944f: 8256308: Send arguments to javac server in a config file
• 8f7caa4: 8256857: ARM32 builds broken after JDK-8254231
• f8d7c5a: 8256922: ppc, ppcle build broken after JDK-8254231
• b52f6c0: 8256736: Zero: GTest tests fail with "unsuppported vm variant"
• e838d71: 8256722: handle VC++:1927 VS2019 in abstract_vm_version
• cc96b0a: 8256813: Simplify WeakProcessor counting of OopStorage entries
• 67a9590: 8256614: AArch64: Add SVE backend implementation for integer min/max
• 372595c: 8256390: ZGC: Relocate in-place instead of having a heap reserve
• 1df94c9: 8256912: Zero builds fail after JDK-8255984
• b3497f9: 8256839: JavaDoc for java.time.Period.negated() method
• ... and 19 more: https://git.openjdk.java.net/jdk/compare/b450e7c1c5dfd07e0c283f0fa65b75ae06b23003...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.

[pliden]

ZGC changes look good.

[fisk]

Looks good.

[cl4es]

@vnkozlov @pliden @fisk - thank you for reviewing!

I ran ZGC tier1-7 testing on linux-x64 and linux-aarch64 overnight, all passed.

/integrate

[openjdk]

@cl4es Since your change was applied there have been 31 commits pushed to the master branch:

• f55ae95: 8256858: C2: Devirtualize PhaseIterGVN-specific methods
• 7b3d095: 8256618: Zero: Linux x86_32 build still fails
• 9e4944f: 8256308: Send arguments to javac server in a config file
• 8f7caa4: 8256857: ARM32 builds broken after JDK-8254231
• f8d7c5a: 8256922: ppc, ppcle build broken after JDK-8254231
• b52f6c0: 8256736: Zero: GTest tests fail with "unsuppported vm variant"
• e838d71: 8256722: handle VC++:1927 VS2019 in abstract_vm_version
• cc96b0a: 8256813: Simplify WeakProcessor counting of OopStorage entries
• 67a9590: 8256614: AArch64: Add SVE backend implementation for integer min/max
• 372595c: 8256390: ZGC: Relocate in-place instead of having a heap reserve
• ... and 21 more: https://git.openjdk.java.net/jdk/compare/b450e7c1c5dfd07e0c283f0fa65b75ae06b23003...master

Your commit was automatically rebased without conflicts.

Pushed as commit fa3cfcd.

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