RFR: 8371955: Support AVX10 floating point comparison instructions [v5]

[Sandhya Viswanathan]

On Fri, 16 Jan 2026 01:22:39 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 incrementally with one additional commit since the last revision:
> 
>   Remove unnecessary CMOV blocks and adjust predicates involving APX and AVX10.2

src/hotspot/cpu/x86/assembler_x86.cpp line 7357:

> 7355: }
> 7356: 
> 7357: void Assembler::ucomxss(XMMRegister dst, Address src) {

ucomxss should be named as vucomxss.
ucomxsd should be named as vucomxsd.

src/hotspot/cpu/x86/x86.ad line 1703:

> 1701: static void emit_cmpfp3(MacroAssembler* masm, Register dst) {
> 1702:   // If any floating point comparison instruction is used, unordered case always triggers jump
> 1703:   // For below condition, CF=1 is true when at least one input is NaN

// for
lowercase f in for.

test/hotspot/jtreg/compiler/c2/irTests/CMoveLConstants.java line 64:

> 62:     @IR(counts = {IRNode.X86_CMOVEL_IMM01UCFE, "1"},
> 63:         applyIfPlatform = {"x64", "true"},
> 64:         applyIfCPUFeature = {"apx_f", "true"},

Need to include avx10_2 check here as well.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/28337#discussion_r2699354660
PR Review Comment: https://git.openjdk.org/jdk/pull/28337#discussion_r2699427353
PR Review Comment: https://git.openjdk.org/jdk/pull/28337#discussion_r2699527070