encoding/json: optimize field sorting with slices and cmp

Refactor field sorting in typeFields to use slices.SortFunc and cmp.Compare,
resulting in performance improvements in cache misses and slight increases in
hit latency. Memory allocation and operation counts also reduced significantly
for cache misses.

goos: darwin
goarch: arm64
pkg: encoding/json
cpu: Apple M2 Max
                                    │   old.txt    │              new.txt               │
                                    │    sec/op    │   sec/op     vs base               │
TypeFieldsCache/MissTypes1-12          5.068µ ± 2%   5.032µ ± 1%       ~ (p=0.055 n=10)
TypeFieldsCache/MissTypes10-12         15.22µ ± 2%   14.79µ ± 2%  -2.84% (p=0.000 n=10)
TypeFieldsCache/MissTypes100-12        98.40µ ± 3%   94.72µ ± 1%  -3.73% (p=0.002 n=10)
TypeFieldsCache/MissTypes1000-12       860.3µ ± 3%   840.7µ ± 1%       ~ (p=0.105 n=10)
TypeFieldsCache/MissTypes10000-12      8.092m ± 3%   7.987m ± 4%       ~ (p=0.280 n=10)
TypeFieldsCache/MissTypes100000-12     80.90m ± 9%   80.62m ± 2%       ~ (p=0.631 n=10)
TypeFieldsCache/MissTypes1000000-12   1009.5m ± 7%   933.8m ± 7%  -7.50% (p=0.011 n=10)
TypeFieldsCache/HitTypes1-12           1.554n ± 3%   1.617n ± 3%  +4.05% (p=0.004 n=10)
TypeFieldsCache/HitTypes10-12          1.575n ± 1%   1.624n ± 6%  +3.14% (p=0.000 n=10)
TypeFieldsCache/HitTypes100-12         1.566n ± 1%   1.627n ± 5%  +3.86% (p=0.000 n=10)
TypeFieldsCache/HitTypes1000-12        1.526n ± 4%   1.596n ± 3%  +4.55% (p=0.001 n=10)
TypeFieldsCache/HitTypes10000-12       1.506n ± 0%   1.573n ± 3%  +4.41% (p=0.000 n=10)
TypeFieldsCache/HitTypes100000-12      1.480n ± 1%   1.529n ± 7%  +3.35% (p=0.001 n=10)
TypeFieldsCache/HitTypes1000000-12     1.473n ± 2%   1.468n ± 2%       ~ (p=0.739 n=10)
geomean                                1.371µ        1.374µ       +0.25%

                                    │     old.txt     │                new.txt                 │
                                    │      B/op       │     B/op       vs base                 │
TypeFieldsCache/MissTypes1-12          2.023Ki ± 0%      2.000Ki ± 0%  -1.16% (p=0.000 n=10)
TypeFieldsCache/MissTypes10-12         10.95Ki ± 0%      10.71Ki ± 0%  -2.17% (p=0.000 n=10)
TypeFieldsCache/MissTypes100-12       101.91Ki ± 0%      99.53Ki ± 0%  -2.34% (p=0.000 n=10)
TypeFieldsCache/MissTypes1000-12      1044.3Ki ± 0%     1020.8Ki ± 0%  -2.25% (p=0.000 n=10)
TypeFieldsCache/MissTypes10000-12      9.957Mi ± 0%      9.730Mi ± 0%  -2.29% (p=0.000 n=10)
TypeFieldsCache/MissTypes100000-12     97.79Mi ± 0%      95.50Mi ± 0%  -2.34% (p=0.000 n=10)
TypeFieldsCache/MissTypes1000000-12   1018.4Mi ± 0%      995.5Mi ± 0%  -2.25% (p=0.000 n=10)
TypeFieldsCache/HitTypes1-12             0.000 ± 0%        0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes10-12            0.000 ± 0%        0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes100-12           0.000 ± 0%        0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes1000-12          0.000 ± 0%        0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes10000-12         0.000 ± 0%        0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes100000-12        0.000 ± 0%        0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes1000000-12       0.000 ± 0%        0.000 ± 0%       ~ (p=1.000 n=10) ¹
geomean                                             ²                  -1.06%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

                                    │    old.txt    │               new.txt                │
                                    │   allocs/op   │  allocs/op   vs base                 │
TypeFieldsCache/MissTypes1-12          46.00 ± 0%      45.00 ± 0%  -2.17% (p=0.000 n=10)
TypeFieldsCache/MissTypes10-12         215.0 ± 0%      205.0 ± 0%  -4.65% (p=0.000 n=10)
TypeFieldsCache/MissTypes100-12       1.845k ± 0%     1.745k ± 0%  -5.42% (p=0.000 n=10)
TypeFieldsCache/MissTypes1000-12      18.08k ± 0%     17.08k ± 0%  -5.53% (p=0.000 n=10)
TypeFieldsCache/MissTypes10000-12     180.3k ± 0%     170.3k ± 0%  -5.55% (p=0.000 n=10)
TypeFieldsCache/MissTypes100000-12    1.804M ± 0%     1.704M ± 0%  -5.54% (p=0.000 n=10)
TypeFieldsCache/MissTypes1000000-12   18.04M ± 0%     17.04M ± 0%  -5.54% (p=0.000 n=10)
TypeFieldsCache/HitTypes1-12           0.000 ± 0%      0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes10-12          0.000 ± 0%      0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes100-12         0.000 ± 0%      0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes1000-12        0.000 ± 0%      0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes10000-12       0.000 ± 0%      0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes100000-12      0.000 ± 0%      0.000 ± 0%       ~ (p=1.000 n=10) ¹
TypeFieldsCache/HitTypes1000000-12     0.000 ± 0%      0.000 ± 0%       ~ (p=1.000 n=10) ¹
geomean                                           ²                -2.49%                ²
¹ all samples are equal
² summaries must be >0 to compute geomean

Change-Id: I62b8f524f5747f4f1b9241a1d849efeef1851049
GitHub-Last-Rev: d16772d
GitHub-Pull-Request: #67046
Reviewed-on: https://go-review.googlesource.com/c/go/+/581895
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Joedian Reid <joedian@google.com>

src/encoding/json/encode.go

@@ -12,13 +12,13 @@ package json
 
 import (
 	"bytes"
+	"cmp"
 	"encoding"
 	"encoding/base64"
 	"fmt"
 	"math"
 	"reflect"
 	"slices"
-	"sort"
 	"strconv"
 	"strings"
 	"sync"
@@ -1162,21 +1162,23 @@ func typeFields(t reflect.Type) structFields {
 		}
 	}
 
-	sort.Slice(fields, func(i, j int) bool {
-		x := fields
+	slices.SortFunc(fields, func(a, b field) int {
 		// sort field by name, breaking ties with depth, then
 		// breaking ties with "name came from json tag", then
 		// breaking ties with index sequence.
-		if x[i].name != x[j].name {
-			return x[i].name < x[j].name
+		if c := strings.Compare(a.name, b.name); c != 0 {
+			return c
 		}
-		if len(x[i].index) != len(x[j].index) {
-			return len(x[i].index) < len(x[j].index)
+		if c := cmp.Compare(len(a.index), len(b.index)); c != 0 {
+			return c
 		}
-		if x[i].tag != x[j].tag {
-			return x[i].tag
+		if a.tag != b.tag {
+			if a.tag {
+				return -1
+			}
+			return +1
 		}
-		return slices.Compare(x[i].index, x[j].index) == -1
+		return slices.Compare(a.index, b.index)
 	})
 
 	// Delete all fields that are hidden by the Go rules for embedded fields,