reflect: optimize DeepEqual() for maps

benchmark                     old ns/op     new ns/op     delta
BenchmarkMapsDeepEqual-10     235           200           -15.05%

benchmark                     old allocs     new allocs     delta
BenchmarkMapsDeepEqual-10     7              6              -14.29%

benchmark                     old bytes     new bytes     delta
BenchmarkMapsDeepEqual-10     96            48            -50.00%

Change-Id: Ifa625ad25524cc9ee438711917606626b33a9597
Reviewed-on: https://go-review.googlesource.com/c/go/+/512576
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: David Chase <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>

Author: korzhao

src/reflect/benchmark_test.go

@@ -107,6 +107,18 @@ func BenchmarkDeepEqual(b *testing.B) {
 	}
 }
 
+func BenchmarkMapsDeepEqual(b *testing.B) {
+	m1 := map[int]int{
+		1: 1, 2: 2,
+	}
+	m2 := map[int]int{
+		1: 1, 2: 2,
+	}
+	for i := 0; i < b.N; i++ {
+		DeepEqual(m1, m2)
+	}
+}
+
 func BenchmarkIsZero(b *testing.B) {
 	source := ValueOf(struct {
 		ArrayComparable    [4]T

src/reflect/deepequal.go

@@ -142,9 +142,10 @@ func deepValueEqual(v1, v2 Value, visited map[visit]bool) bool {
 		if v1.UnsafePointer() == v2.UnsafePointer() {
 			return true
 		}
-		for _, k := range v1.MapKeys() {
-			val1 := v1.MapIndex(k)
-			val2 := v2.MapIndex(k)
+		iter := v1.MapRange()
+		for iter.Next() {
+			val1 := iter.Value()
+			val2 := v2.MapIndex(iter.Key())
 			if !val1.IsValid() || !val2.IsValid() || !deepValueEqual(val1, val2, visited) {
 				return false
 			}