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cmp: optimize Compare #63360

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cmp: optimize Compare #63360

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@ncruces ncruces commented Oct 3, 2023 •
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Compare provides three-way comparison for Ordered types, which certain
algorithms benefit from.

Float comparisons require NaN handling that should be optimized away for
all other types.
String comparisons benefit from using != which short-circuits on
different length strings.
Ideally the compiler would recognize the pattern and specialize on
strings, but this tries to improve the status quo.

goos: darwin
goarch: amd64
pkg: cmp
cpu: Intel(R) Core(TM) i7-8750H CPU @ 2.20GHz
│ base.txt │ patch.txt │
│ sec/op │ sec/op vs base │
Compare_int-12 1.638n ± 1% 1.635n ± 2% ~ (p=0.698 n=10)
Compare_float64-12 2.397n ± 1% 2.206n ± 0% -7.99% (p=0.000 n=10)
Compare_strings-12 8.054n ± 1% 6.705n ± 2% -16.75% (p=0.000 n=10)
geomean 3.162n 2.892n -8.56%

Updates #31187
Updates #61725

@ncruces
cmp: optimize Compare
e776e0e 
Compare provides three-way comparison for Ordered types,
which certain algorithms benefit from.

Float comparisons require NaN handling that should be
optimized away for all other types.
String comparisons benefit from trying == first and
short-circuiting on different length strings.
Ideally the compiler would recognize the pattern and
specialize on strings, but this improves the status quo.

Benchmark shows:
- no change for ints,
- 20% improvement for floats, and
- 25% improvement for strings.

Bug: #61725
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This PR (HEAD: e776e0e) has been imported to Gerrit for code review.

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Patch Set 2:

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Patch Set 3:

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Patch Set 3:

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This PR (HEAD: d74b2a9) has been imported to Gerrit for code review.

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Message from Nuno Cruces:

Patch Set 3:

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Patch Set 4:

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Message from Ian Lance Taylor:

Patch Set 5: Commit-Queue+1

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Message from Go LUCI:

Patch Set 5:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2023-10-08T14:59:37Z","revision":"fc0504b8aaaabdb68448a8d09a52ba3ddc6789c8"}

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Message from Ian Lance Taylor:

Patch Set 5: -Commit-Queue

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This CL has passed the run

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Patch Set 5:

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Message from Nuno Cruces:

Patch Set 5:

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This PR (HEAD: b3bfbdf) has been imported to Gerrit for code review.

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Message from Nuno Cruces:

Patch Set 6:

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Patch Set 7:

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Message from Nuno Cruces:

Patch Set 7:

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ncruces commented Oct 14, 2024

https://go-review.googlesource.com/c/go/+/578835

@ncruces ncruces closed this Oct 14, 2024
@ncruces ncruces deleted the cmp branch October 14, 2024 15:01
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