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8315554: C1: Replace "cmp reg, 0" with "test reg, reg" on x86 #15543

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@shipilev shipilev commented Sep 1, 2023

Noticed this when looking at C1 profiling code. There are plenty of usages for cmp reg, 0 in C1 x86 code, both in generic LIR_Assembler::comp_op, and in some profiling paths.

test reg, reg is a denser idiom for this comparison. The difference between cmp and test on x86 seems to be only with AF (aux carry flag). For ubiquitous int/pointer comparisons, this distinction is irrelevant.

C2 already does this transformation in .ad match rules.

Code size improvements with -Xcomp -XX:+CITime -XX:TieredStopAtLevel=... Hello:

# Before 
 tier1: nmethod total size: 430104 bytes
 tier2: nmethod total size: 467336 bytes
 tier3: nmethod total size: 923384 bytes

# After
 tier1: nmethod total size: 427584 bytes (-0.59%)
 tier2: nmethod total size: 464352 bytes (-0.64%)
 tier3: nmethod total size: 918328 bytes (-0.55%)

Additional testing:

  • Linux x86_64 tier1 tier2 tier3 x (C1 level 1, 2, 3) x (Parallel, G1, Shenandoah)

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  • JDK-8315554: C1: Replace "cmp reg, 0" with "test reg, reg" on x86 (Enhancement - P4)

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👋 Welcome back shade! 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.

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openjdk bot commented Sep 1, 2023

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

  • hotspot-compiler

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

@openjdk openjdk bot added the hotspot-compiler hotspot-compiler-dev@openjdk.org label Sep 1, 2023
@shipilev shipilev marked this pull request as ready for review September 4, 2023 19:00
@openjdk openjdk bot added the rfr Pull request is ready for review label Sep 4, 2023
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Webrevs

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openjdk bot commented Sep 4, 2023

@shipilev 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:

8315554: C1: Replace "cmp reg, 0" with "test reg, reg" on x86

Reviewed-by: iveresov, chagedorn, thartmann

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 38 new commits pushed to the master branch:

  • 5cbff24: 8315406: [REDO] serviceability/jdwp/AllModulesCommandTest.java ignores VM flags
  • 7a08e6b: 8313575: Refactor PKCS11Test tests
  • d3ee704: 8315563: Remove references to JDK-8226420 from problem list
  • aba89f2: 8312213: Remove unnecessary TEST instructions on x86 when flags reg will already be set
  • 1f4cdb3: 8315127: CDSMapTest fails with incorrect number of oop references
  • 939d7c5: 8161536: sun/security/pkcs11/sslecc/ClientJSSEServerJSSE.java fails with ProviderException
  • ebe3127: 8315717: ProblemList serviceability/sa/TestHeapDumpForInvokeDynamic.java with ZGC
  • 969fcdb: 8314191: C2 compilation fails with "bad AD file"
  • cef9fff: 8305507: Add support for grace period before AbortVMOnSafepointTimeout triggers
  • ed2b467: 8315499: build using devkit on Linux ppc64le RHEL puts path to devkit into libsplashscreen
  • ... and 28 more: https://git.openjdk.org/jdk/compare/b4f7069c5b60335fb51d7a3f15c61edce7f158d1...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.

@openjdk openjdk bot added the ready Pull request is ready to be integrated label Sep 4, 2023
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Looks good!

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Looks good.

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shipilev commented Sep 6, 2023

Our tests here look fine. Mind if I ask @TobiHartmann, @chhagedorn or @veresov to give this one a spin in Oracle test CIs?

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Already done - results look good on Windows and Linux! We currently have quite a load for MacOS testing, so it will probably not finish in a timely manner. But I guess it's fine to not wait for that and move forward.

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shipilev commented Sep 6, 2023

All right then!

/integrate

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openjdk bot commented Sep 6, 2023

Going to push as commit bd47781.
Since your change was applied there have been 47 commits pushed to the master branch:

  • 25e85db: 8307468: CDS Lambda Proxy classes are regenerated in dynamic dump
  • 024133b: 8311964: Some jtreg tests failing on x86 with error 'unrecognized VM options' (C2 flags)
  • 62a953f: 8315689: G1: Remove unused init_hash_seed
  • cfc1489: 8315579: SPARC64 builds are broken after JDK-8304913
  • f6c203e: 8314949: linux PPC64 Big Endian: Implementation of Foreign Function & Memory API
  • a01b3fb: 8288660: JavaDoc should be more helpful if it doesn't recognize a tag
  • ba1a463: 8315377: C2: assert(u->find_out_with(Op_AddP) == nullptr) failed: more than 2 chained AddP nodes?
  • a258fc4: 8315648: Add test for JDK-8309979 changes
  • 5d3fdc1: 8315612: RISC-V: intrinsic for unsignedMultiplyHigh
  • 5cbff24: 8315406: [REDO] serviceability/jdwp/AllModulesCommandTest.java ignores VM flags
  • ... and 37 more: https://git.openjdk.org/jdk/compare/b4f7069c5b60335fb51d7a3f15c61edce7f158d1...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Sep 6, 2023
@openjdk openjdk bot closed this Sep 6, 2023
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Sep 6, 2023
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openjdk bot commented Sep 6, 2023

@shipilev Pushed as commit bd47781.

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

@shipilev shipilev deleted the JDK-8315554-c1-cmp-0-test branch November 28, 2023 14:50
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