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8324724: Add Stub routines for FP16 conversions on aarch64 #17706

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@Bhavana-Kilambi Bhavana-Kilambi commented Feb 5, 2024

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)

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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

Webrev

Link to Webrev Comment

This commit - openjdk@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.
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👋 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.

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@Bhavana-Kilambi 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 Feb 5, 2024
@Bhavana-Kilambi Bhavana-Kilambi marked this pull request as ready for review February 5, 2024 09:15
@openjdk openjdk bot added the rfr Pull request is ready for review label Feb 5, 2024
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Webrevs

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openjdk bot commented Feb 5, 2024

@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

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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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@openjdk openjdk bot added the ready Pull request is ready to be integrated label Feb 5, 2024
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/integrate

@openjdk openjdk bot added the sponsor Pull request is ready to be sponsored label Feb 5, 2024
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openjdk bot commented Feb 5, 2024

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

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nick-arm commented Feb 5, 2024

/sponsor

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openjdk bot commented Feb 5, 2024

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

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Feb 5, 2024
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@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
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This change is causing crashes on macOS - JDK-8325264

@TobiHartmann
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@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!

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

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