RFR: 8371955: Support AVX10 floating point comparison instructions [v8]

[Emanuel Peter]

On Fri, 23 Jan 2026 23:04:43 GMT, Mohamed Issa <missa at openjdk.org> wrote:

>> Intel® AVX10 ISA [1] extensions added new floating point comparison instructions. They set the EFLAGS register so that relationships can be tested independently to avoid extra checks when one of the inputs is NaN.
>> 
>> Most of the work is covered in the architecture definition (`x86.ad`) file. A new comparison operand was created to be used by new CMove and JMP definitions with the APX specific portions of the CMove section being updated to rely on the new instructions because both sets of instructions are always expected to be available on the same platform. New floating point comparison definitions were also added.
>> 
>> This change uses the new AVX10.2 (UCOMXSS or UCOMXSD) instructions on supported platforms to avoid the extra handling required with existing (UCOMISS or UCOMISD) instructions. To make sure no new failures were introduced, tier1, tier2, and tier3 tests were run on builds with and without the changes. Additionally, the JTREG tests listed below were used to verify correctness with `-XX:-UseAPX` / `-XX:+UseAPX` options. The baseline build used is [OpenJDK v26-b26](https://github.com/openjdk/jdk/releases/tag/jdk-26%2B26).
>> 
>> 1. `jtreg:test/hotspot/jtreg/compiler/c2/irTests/CMoveLConstants.java`
>> 2. `jtreg:test/hotspot/jtreg/compiler/c2/irTests/TestFPComparison.java`
>> 3. `jtreg:test/hotspot/jtreg/compiler/intrinsics/math/TestSignumIntrinsic.java`
>> 4. `jtreg:test/hotspot/jtreg/compiler/vectorization/TestSignumVector.java`
>> 
>> Finally, the JMH micro-benchmark listed below was updated to separately exercise CMove and JMP code paths.
>> 
>> 1. `micro:test/micro/org/openjdk/bench/java/lang/FPComparison.java`
>> 
>> [1] https://www.intel.com/content/www/us/en/content-details/856721/intel-advanced-vector-extensions-10-2-intel-avx10-2-architecture-specification.html?wapkw=AVX10
>
> Mohamed Issa has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 25 commits:
> 
>  - Merge branch 'master' into user/missa-prime/avx10_2
>  - Merge branch 'master' into user/missa-prime/avx10_2
>  - Change function names and extend IR encoding rules for CMove tests
>  - Merge remote-tracking branch 'origin/master' into user/missa-prime/avx10_2
>  - Remove unnecessary CMOV blocks and adjust predicates involving APX and AVX10.2
>  - Remove extra jump instruction in signum floating point and unify three-way floating point comparison logic in x86.ad
>  - Also update copyright year in IREncodingPrinter.java
>  - Include apx_f in list of verified CPU features for IR encoding
>  - Fix CMove IR tests to account for APX presence
>  - Merge branch 'master' into user/missa-prime/avx10_2
>  - ... and 15 more: https://git.openjdk.org/jdk/compare/44b74e16...09d1e44d

test/hotspot/jtreg/compiler/c2/irTests/CMoveLConstants.java line 65:

> 63:         applyIfPlatform = {"x64", "true"},
> 64:         applyIfCPUFeatureAnd = {"apx_f", "true", "avx10_2", "true"},
> 65:         phase = CompilePhase.FINAL_CODE)

These are all `CMove` cases. I see you added branch/call cases in the benchmark. Would it make sense to have some similar cases here?

And: this here is a test for `float`. Where do we cover `double`, which you are also making VM changes for?

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PR Review Comment: https://git.openjdk.org/jdk/pull/28337#discussion_r2730715729