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8288992: AArch64: CMN should be handled the same way as CMP #9246

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@theRealAph theRealAph commented Jun 22, 2022

At present, cmp(r8, -1) fails at compile time, but cmn(r8, -1) fails at runtime. We should fix cmn() to be the same as cmp().

After this change, it's much less likely that we'll be surprised by immediate overflows in cmn().


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  • JDK-8288992: AArch64: CMN should be handled the same way as CMP

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bridgekeeper bot commented Jun 22, 2022

👋 Welcome back aph! 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 openjdk bot added the rfr Pull request is ready for review label Jun 22, 2022
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@theRealAph The following label will be automatically applied to this pull request:

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mlbridge bot commented Jun 22, 2022

Webrevs

@@ -197,8 +197,11 @@ class MacroAssembler: public Assembler {
inline void cmp(Register Rd, unsigned char imm8) { subs(zr, Rd, imm8); }
inline void cmp(Register Rd, unsigned imm) = delete;

inline void cmnw(Register Rd, unsigned imm) { addsw(zr, Rd, imm); }
inline void cmn(Register Rd, unsigned imm) { adds(zr, Rd, imm); }
template<class T>
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Why do we need it to be a template?

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If we made it unsigned int, we'd risk a 64-bit signed value (from C2, for example) being truncated before being passed to addsw(Register Rd, Register Rn, uint64_t imm). As we now have a 64-bit-clean path through all this code, that would be a Bad Thing.

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Thank you for the explanation. I reread the code and found why I got confused.
MacroAssembler::cmnw call addsw which is defined by WRAP(addsw, true).
The macro expends to

void addsw(Register Rd, Register Rn, uint64_t imm) {
    wrap_adds_subs_imm_insn(Rd, Rn, imm, &Assembler::addsw, &Assembler::addsw, true);
}

void addsw(Register Rd, Register Rn, Register Rm, enum shift_kind kind, unsigned shift = 0) {
   Assembler::addsw(Rd, Rn, Rm, kind, shift);
}

void addsw(Register Rd, Register Rn, Register Rm) {
   Assembler::addsw(Rd, Rn, Rm);
}

void addsw(Register Rd, Register Rn, Register Rm, ext::operation option, int amount = 0) {
  Assembler::addsw(Rd, Rn, Rm, option, amount);
}

I've mixed it up with Assembler::addsw(Register Rd, Register Rn, unsigned imm):

#define INSN(NAME, decode, negated)                                     \
  void NAME(Register Rd, Register Rn, unsigned imm, unsigned shift) {   \
    starti;                                                             \
    f(decode, 31, 29), f(0b10001, 28, 24), f(shift, 23, 22), f(imm, 21, 10); \
    zrf(Rd, 0), srf(Rn, 5);                                             \
  }                                                                     \
                                                                        \
  void NAME(Register Rd, Register Rn, unsigned imm) {                   \
    starti;                                                             \
    add_sub_immediate(current_insn, Rd, Rn, imm, decode, negated);      \
  }

  INSN(addsw, 0b001, 0b011);

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lgtm

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Looks good.

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openjdk bot commented Jul 4, 2022

@theRealAph 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:

8288992: AArch64: CMN should be handled the same way as CMP

Reviewed-by: adinn, ngasson

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 195 new commits pushed to the master branch:

  • b5d9656: 8288971: AArch64: Clean up stack and register handling in interpreter
  • d53b02e: 8287312: G1: Early return on first failure in VerifyRegionClosure
  • a8edd7a: 8289569: [test] java/lang/ProcessBuilder/Basic.java fails on Alpine/musl
  • e31003a: 8289575: G1: Remove unnecessary is-marking-active check in G1BarrierSetRuntime::write_ref_field_pre_entry
  • 8e7a3cb: 8289431: (zipfs) Avoid redundant HashMap.get in ZipFileSystemProvider.removeFileSystem
  • 649f2d8: 8065097: [macosx] javax/swing/Popup/TaskbarPositionTest.java fails because Popup is one pixel off
  • d8444aa: 8286610: Add additional diagnostic output to java/net/DatagramSocket/InterruptibleDatagramSocket.java
  • 70f5693: Merge
  • f5cdaba: 8245268: -Xcomp is missing from java launcher documentation
  • 9515560: 8288703: GetThreadState returns 0 for virtual thread that has terminated
  • ... and 185 more: https://git.openjdk.org/jdk/compare/cc445926cfe41ee7803791fb223504b0d9fd8100...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 Jul 4, 2022
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I tested tier1-3.

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/integrate

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openjdk bot commented Jul 6, 2022

Going to push as commit cc2b792.
Since your change was applied there have been 216 commits pushed to the master branch:

  • 75c0a5b: 8288824: [arm32] Display isetstate in register output
  • 83a5d59: 8278479: RunThese test failure with +UseHeavyMonitors and +VerifyHeavyMonitors
  • cbaf6e8: 8288022: c2: Transform (CastLL (AddL into (AddL (CastLL when possible
  • 8341895: 8289739: Add G1 specific GC breakpoints for testing
  • ac6be16: 8289695: [TESTBUG] TestMemoryAwareness.java fails on cgroups v2 and crun
  • 4ad18cf: 8289730: Deprecated code sample in java.lang.ClassCastException
  • d8f4e97: 8289146: containers/docker/TestMemoryWithCgroupV1.java fails on linux ppc64le machine with missing Memory and Swap Limit output
  • f783244: 8289706: (cs) Avoid redundant TreeMap.containsKey call in AbstractCharsetProvider
  • fafe8b3: 8289604: compiler/vectorapi/VectorLogicalOpIdentityTest.java failed on x86 AVX1 system
  • 3515604: 8280481: Duplicated stubs to interpreter for static calls
  • ... and 206 more: https://git.openjdk.org/jdk/compare/cc445926cfe41ee7803791fb223504b0d9fd8100...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Jul 6, 2022
@openjdk openjdk bot closed this Jul 6, 2022
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jul 6, 2022
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openjdk bot commented Jul 6, 2022

@theRealAph Pushed as commit cc2b792.

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

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