labels: use slices.Sort for better performance

The difference is modest, but we've used `slices.Sort` in lots of other
places so why not here.

name     old time/op    new time/op    delta
Builder    1.04µs ± 3%    0.95µs ± 3%   -8.27%  (p=0.008 n=5+5)

name     old alloc/op   new alloc/op   delta
Builder      312B ± 0%      288B ± 0%   -7.69%  (p=0.008 n=5+5)

name     old allocs/op  new allocs/op  delta
Builder      2.00 ± 0%      1.00 ± 0%  -50.00%  (p=0.008 n=5+5)

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

model/labels/labels.go

@@ -18,11 +18,11 @@ package labels
 import (
 	"bytes"
 	"encoding/json"
-	"sort"
 	"strconv"
 
 	"github.com/cespare/xxhash/v2"
 	"github.com/prometheus/common/model"
+	"golang.org/x/exp/slices"
 )
 
 // Well-known label names used by Prometheus components.
@@ -360,7 +360,7 @@ func EmptyLabels() Labels {
 func New(ls ...Label) Labels {
 	set := make(Labels, 0, len(ls))
 	set = append(set, ls...)
-	sort.Sort(set)
+	slices.SortFunc(set, func(a, b Label) bool { return a.Name < b.Name })
 
 	return set
 }
@@ -384,7 +384,7 @@ func FromStrings(ss ...string) Labels {
 		res = append(res, Label{Name: ss[i], Value: ss[i+1]})
 	}
 
-	sort.Sort(res)
+	slices.SortFunc(res, func(a, b Label) bool { return a.Name < b.Name })
 	return res
 }
 
@@ -564,7 +564,7 @@ Outer:
 	}
 	if len(b.add) > 0 { // Base is already in order, so we only need to sort if we add to it.
 		res = append(res, b.add...)
-		sort.Sort(res)
+		slices.SortFunc(res, func(a, b Label) bool { return a.Name < b.Name })
 	}
 	return res
 }
@@ -591,7 +591,7 @@ func (b *ScratchBuilder) Add(name, value string) {
 
 // Sort the labels added so far by name.
 func (b *ScratchBuilder) Sort() {
-	sort.Sort(b.add)
+	slices.SortFunc(b.add, func(a, b Label) bool { return a.Name < b.Name })
 }
 
 // Asssign is for when you already have a Labels which you want this ScratchBuilder to return.

model/labels/labels_string.go

@@ -19,12 +19,12 @@ import (
 	"bytes"
 	"encoding/json"
 	"reflect"
-	"sort"
 	"strconv"
 	"unsafe"
 
 	"github.com/cespare/xxhash/v2"
 	"github.com/prometheus/common/model"
+	"golang.org/x/exp/slices"
 )
 
 // Well-known label names used by Prometheus components.
@@ -385,7 +385,7 @@ func yoloBytes(s string) (b []byte) {
 // New returns a sorted Labels from the given labels.
 // The caller has to guarantee that all label names are unique.
 func New(ls ...Label) Labels {
-	sort.Sort(labelSlice(ls))
+	slices.SortFunc(ls, func(a, b Label) bool { return a.Name < b.Name })
 	size := labelsSize(ls)
 	buf := make([]byte, size)
 	marshalLabelsToSizedBuffer(ls, buf)
@@ -411,7 +411,7 @@ func FromStrings(ss ...string) Labels {
 		ls = append(ls, Label{Name: ss[i], Value: ss[i+1]})
 	}
 
-	sort.Sort(labelSlice(ls))
+	slices.SortFunc(ls, func(a, b Label) bool { return a.Name < b.Name })
 	return New(ls...)
 }
 
@@ -595,8 +595,8 @@ func (b *Builder) Labels(res Labels) Labels {
 		return b.base
 	}
 
-	sort.Sort(labelSlice(b.add))
-	sort.Strings(b.del)
+	slices.SortFunc(b.add, func(a, b Label) bool { return a.Name < b.Name })
+	slices.Sort(b.del)
 	a, d := 0, 0
 
 	buf := make([]byte, 0, len(b.base.data)) // TODO: see if we can re-use the buffer from res.
@@ -753,7 +753,7 @@ func (b *ScratchBuilder) Add(name, value string) {
 
 // Sort the labels added so far by name.
 func (b *ScratchBuilder) Sort() {
-	sort.Sort(labelSlice(b.add))
+	slices.SortFunc(b.add, func(a, b Label) bool { return a.Name < b.Name })
 }
 
 // Asssign is for when you already have a Labels which you want this ScratchBuilder to return.