planner: use slices to eliminate branch check (#50911)

ref #47275

pkg/planner/core/flat_plan.go

@@ -16,7 +16,7 @@ package core
 
 import (
 	"fmt"
-	"sort"
+	"slices"
 
 	"github.com/pingcap/tidb/pkg/kv"
 	"github.com/pingcap/tidb/pkg/util/logutil"
@@ -456,20 +456,16 @@ func (f *FlatPhysicalPlan) flattenForeignKeyChecksAndCascadesMap(childCtx *opera
 	for tid := range fkChecksMap {
 		tids = append(tids, tid)
 	}
-	// Sort by table id for explain result stable.
-	sort.Slice(tids, func(i, j int) bool {
-		return tids[i] < tids[j]
-	})
+	// sort by table id for explain result stable.
+	slices.Sort(tids)
 	for i, tid := range tids {
 		target, childIdxs = f.flattenForeignKeyChecksAndCascades(childCtx, target, childIdxs, fkChecksMap[tid], nil, len(fkCascadesMap) == 0 && i == len(tids)-1)
 	}
 	tids = tids[:0]
 	for tid := range fkCascadesMap {
 		tids = append(tids, tid)
 	}
-	sort.Slice(tids, func(i, j int) bool {
-		return tids[i] < tids[j]
-	})
+	slices.Sort(tids)
 	for i, tid := range tids {
 		target, childIdxs = f.flattenForeignKeyChecksAndCascades(childCtx, target, childIdxs, nil, fkCascadesMap[tid], i == len(tids)-1)
 	}

pkg/planner/core/rule_join_reorder_greedy.go

@@ -15,8 +15,9 @@
 package core
 
 import (
+	"cmp"
 	"math"
-	"sort"
+	"slices"
 
 	"github.com/pingcap/tidb/pkg/expression"
 )
@@ -57,8 +58,8 @@ func (s *joinReorderGreedySolver) solve(joinNodePlans []LogicalPlan, tracer *joi
 		}
 	}
 	// Sort plans by cost
-	sort.SliceStable(s.curJoinGroup, func(i, j int) bool {
-		return s.curJoinGroup[i].cumCost < s.curJoinGroup[j].cumCost
+	slices.SortStableFunc(s.curJoinGroup, func(i, j *jrNode) int {
+		return cmp.Compare(i.cumCost, j.cumCost)
 	})
 
 	// joinNodeNum indicates the number of join nodes except leading join nodes in the current join group