8324724: Add Stub routines for FP16 conversions on aarch64

[Bhavana-Kilambi]

This commit - 8cfd74f adds stub routines for FP16 conversions for float/float16 constants on x86 to get an accurate compile time value of the nodes. This task adds similar stub routines for aarch64 as well.

With this patch, if the inputs to the conversion functions are constants, the stub routines are executed to determine the compile time values of the ConvHF2F/ConvF2HF nodes (in their respective Value() functions) and the ConvHF2F/ConvF2HF nodes are replaced with ConI/ConF nodes. This might help in further compiler optimizations like constant folding.

The following testcase was used to test the disassembly -

public class FloatConv {

    private static final short sconst;
    private static final float fconst;

    static {
        sconst = Short.MAX_VALUE;
        fconst = Float.MIN_VALUE;
    }

    @Benchmark
    public float hf2f() {
        return Float.float16ToFloat(sconst);
    }

    @Benchmark
    public short f2hf() {
        return Float.floatToFloat16(fconst);
    }
}

Disassembly without patch :

FloatConv.f2hf() :-

...
ldr   s17, 0x0000ffff918cec80
fcvt  h16, s17
smov  x0, v16.h[0]
...
ret

FloatConv.hf2f() :-

...
orr   w11, wzr, #0x7fff
mov   v16.h[0], w11
fcvt  s0, h16
...
ret

Disassembly with patch :

FloatConv.hf2f() :-

...
ldr   s0, 0x0000ffffb58ce880
...
ret

FloatConv.f2hf() :-

...
mov   w0, wzr
...
ret

With this patch, the conversion computation is done well in advance and the ConvHF2F/ConvF2HF nodes are replaced with the ConI/ConF nodes and thus the constant values are just loaded into registers and returned.

The tests in - "hotspot/jtreg/compiler/intrinsics/float16" pass on both aarch64 and x86.

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8324724: Add Stub routines for FP16 conversions on aarch64 (Enhancement - P4)

Reviewers

• Andrew Haley (@theRealAph - Reviewer)
• Nick Gasson (@nick-arm - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/17706/head:pull/17706
$ git checkout pull/17706

Update a local copy of the PR:
$ git checkout pull/17706
$ git pull https://git.openjdk.org/jdk.git pull/17706/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 17706

View PR using the GUI difftool:
$ git pr show -t 17706

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/17706.diff

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[bridgekeeper]

👋 Welcome back bkilambi! 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]

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[mlbridge]

Webrevs

• 00: Full (fd73a80c)

[openjdk]

@Bhavana-Kilambi 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:

8324724: Add Stub routines for FP16 conversions on aarch64

Reviewed-by: aph, 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 2 new commits pushed to the master branch:

• 0377f1a: 8325133: Missing MEMFLAGS parameter in parts of os API
• df35462: 8323502: javac crash with wrongly typed method block in Flow

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
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.

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➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

[Bhavana-Kilambi]

/integrate

[openjdk]

@Bhavana-Kilambi
Your change (at version fd73a80) is now ready to be sponsored by a Committer.

[nick-arm]

/sponsor

[openjdk]

Going to push as commit 51853f7.
Since your change was applied there have been 11 commits pushed to the master branch:

• c3adc61: 8325199: (zipfs) jdk/nio/zipfs/TestPosix.java failed 6 sub-tests
• 1993652: 8324983: race in CompileBroker::possibly_add_compiler_threads
• 55c1446: 8321468: Remove StringUTF16::equals
• 19e9220: 8325169: Reduce String::indexOf overheads
• 89e6a02: 8325064: C2 SuperWord: refactor construct_bb
• d395ac2: 8321373: Build should use LC_ALL=C.UTF-8
• 51671c0: 8323809: Serial: Refactor card table verification
• cdf918b: 8325134: Serial: Remove Generation::used_region
• 4da28b4: 8291809: Convert compiler/c2/cr7200264/TestSSE2IntVect.java to IR verification test
• 0377f1a: 8325133: Missing MEMFLAGS parameter in parts of os API
• ... and 1 more: https://git.openjdk.org/jdk/compare/af32262c28f6dd012307c249156d909bb891e75b...master

Your commit was automatically rebased without conflicts.

[openjdk]

@nick-arm @Bhavana-Kilambi Pushed as commit 51853f7.

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

[dholmes-ora]

This change is causing crashes on macOS - JDK-8325264

[TobiHartmann]

@Bhavana-Kilambi Please allow for enough time for reviews, at least 24 hours, see https://openjdk.org/guide/#life-of-a-pr. We usually perform some sanity testing, which would have caught the issues reported in JDK-8325264. Thanks!

[Bhavana-Kilambi]

Apologies. I will take a look at the failures right away ..