[go] internal/bytealg: use NEON for compare_arm64.s large-input path

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Jul 16, 2026, 12:48:46 PM (yesterday) Jul 16

to Gerrit Bot, Mauri de Souza Meneguzzo, goph...@pubsubhelper.golang.org, golang-...@googlegroups.com, Michael Pratt, Keith Randall, Keith Randall, golang...@luci-project-accounts.iam.gserviceaccount.com, golang-co...@googlegroups.com

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Commit message:

internal/bytealg: use NEON for compare_arm64.s large-input path

Replace the scalar chunk loop with a 64-byte/iter NEON loop.

For inputs >= 64 bytes, each iteration loads and compares 64 bytes from
both sides using NEON. The compare results are reduced to a single byte;
zero indicates a mismatch.

On mismatch, both pointers are rewound by 64 bytes and the existing
scalar chunk16 path locates the first differing byte pair and produces
the lexicographic result. This fallback is taken at most once.

Inputs < 64 bytes continue to use the existing scalar chunk16 and tail
paths unchanged.

This brings the overall structure closer to equal_arm64.s.

     goos: darwin
     goarch: arm64
     pkg: bytes
     cpu: Apple M3 Pro
                                              │   old.txt   │                new.txt                │
                                              │   sec/op    │   sec/op     vs base                  │
     CompareBytesBigUnaligned/offset=1-11       26.55µ ± 1%   19.21µ ± 1%  -27.63% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=2-11       26.83µ ± 3%   19.11µ ± 1%  -28.78% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=3-11       26.59µ ± 1%   19.28µ ± 2%  -27.50% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=4-11       26.49µ ± 1%   19.11µ ± 1%  -27.84% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=5-11       27.04µ ± 3%   19.05µ ± 1%  -29.54% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=6-11       27.12µ ± 1%   18.92µ ± 1%  -30.24% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=7-11       27.00µ ± 0%   18.90µ ± 0%  -30.01% (p=0.000 n=10)
     CompareBytesBigBothUnaligned/offset=0-11   26.56µ ± 1%   18.01µ ± 1%  -32.20% (p=0.000 n=10)
     CompareBytesBigBothUnaligned/offset=1-11   27.27µ ± 1%   19.43µ ± 0%  -28.77% (p=0.000 n=10)
     CompareBytesBigBothUnaligned/offset=2-11   26.83µ ± 2%   18.68µ ± 1%  -30.38% (p=0.000 n=10)
     CompareBytesBigBothUnaligned/offset=3-11   27.24µ ± 0%   19.45µ ± 0%  -28.62% (p=0.000 n=10)
     CompareBytesBigBothUnaligned/offset=4-11   27.07µ ± 1%   18.67µ ± 1%  -31.03% (p=0.000 n=7+10)
     geomean                                    26.88µ        10.82µ       -29.39%

                                              │   old.txt    │                new.txt                 │
                                              │     B/s      │     B/s       vs base                  │
     CompareBytesBigUnaligned/offset=1-11       36.78Gi ± 1%   50.82Gi ± 1%  +38.18% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=2-11       36.40Gi ± 3%   51.11Gi ± 1%  +40.41% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=3-11       36.73Gi ± 1%   50.66Gi ± 2%  +37.93% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=4-11       36.87Gi ± 1%   51.09Gi ± 1%  +38.59% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=5-11       36.12Gi ± 3%   51.27Gi ± 1%  +41.92% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=6-11       36.00Gi ± 1%   51.61Gi ± 1%  +43.35% (p=0.000 n=10)
     CompareBytesBigUnaligned/offset=7-11       36.17Gi ± 0%   51.68Gi ± 0%  +42.88% (p=0.000 n=10)
     CompareBytesBigBothUnaligned/offset=0-11   36.77Gi ± 1%   54.23Gi ± 1%  +47.48% (p=0.000 n=10)
     CompareBytesBigBothUnaligned/offset=1-11   35.81Gi ± 1%   50.27Gi ± 0%  +40.39% (p=0.000 n=10)
     CompareBytesBigBothUnaligned/offset=2-11   36.40Gi ± 2%   52.29Gi ± 1%  +43.64% (p=0.000 n=10)
     CompareBytesBigBothUnaligned/offset=3-11   35.85Gi ± 0%   50.22Gi ± 0%  +40.09% (p=0.000 n=10)
     CompareBytesBigBothUnaligned/offset=4-11   36.07Gi ± 1%   52.30Gi ± 1%  +45.00% (p=0.000 n=7+10)
     geomean                                    36.33Gi        90.30Gi       +41.63%

Change-Id: I4ce9a26f7d434eb4f6447d8a5cbebee5d0901753

GitHub-Last-Rev: 1bf14dc111f1a848cce2193af0f17170b1dc7e73

GitHub-Pull-Request: golang/go#79800

Reviewed-on: https://go-review.googlesource.com/c/go/+/786560

Auto-Submit: Keith Randall <k...@golang.org>

Reviewed-by: Michael Pratt <mpr...@google.com>

LUCI-TryBot-Result: golang...@luci-project-accounts.iam.gserviceaccount.com <golang...@luci-project-accounts.iam.gserviceaccount.com>

Reviewed-by: Keith Randall <k...@golang.org>

Reviewed-by: Keith Randall <k...@google.com>

Files:

M src/internal/bytealg/compare_arm64.s

Change size: M

Delta: 1 file changed, 47 insertions(+), 29 deletions(-)

Branch: refs/heads/master

Submit Requirements:

Code-Review: +2 by Keith Randall, +1 by Keith Randall, +1 by Michael Pratt
TryBots-Pass: LUCI-TryBot-Result+1 by golang...@luci-project-accounts.iam.gserviceaccount.com

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