encoding/json: optimize Unmarshal for maps

benchmark                    old ns/op     new ns/op     delta
BenchmarkUnmarshalMap-10     218           172           -21.28%

benchmark                    old allocs     new allocs     delta
BenchmarkUnmarshalMap-10     15             12             -20.00%

benchmark                    old bytes     new bytes     delta
BenchmarkUnmarshalMap-10     328           256           -21.95%

Change-Id: Ie20ab62731c752eb0040c6d1591fedd7d12b1e0c
Reviewed-on: https://go-review.googlesource.com/c/go/+/514100
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/encoding/json/bench_test.go b/src/encoding/json/bench_test.go
index d3af0dc0ed..bafccdf193 100644
--- a/src/encoding/json/bench_test.go
+++ b/src/encoding/json/bench_test.go
@@ -385,6 +385,19 @@ func BenchmarkUnmarshalInt64(b *testing.B) {
 	})
 }
 
+func BenchmarkUnmarshalMap(b *testing.B) {
+	b.ReportAllocs()
+	data := []byte(`{"key1":"value1","key2":"value2","key3":"value3"}`)
+	b.RunParallel(func(pb *testing.PB) {
+		x := make(map[string]string, 3)
+		for pb.Next() {
+			if err := Unmarshal(data, &x); err != nil {
+				b.Fatal("Unmarshal:", err)
+			}
+		}
+	})
+}
+
 func BenchmarkIssue10335(b *testing.B) {
 	b.ReportAllocs()
 	j := []byte(`{"a":{ }}`)