Commit 75e7e05a authored by Daniel Martí's avatar Daniel Martí

encoding/json: inline fieldByIndex

This function was only used in a single place - in the field encoding
loop within the struct encoder.

Inlining the function call manually lets us get rid of the call
overhead. But most importantly, it lets us simplify the logic afterward.
We no longer need to use reflect.Value{} and !fv.IsValid(), as we can
skip the field immediately.

The two factors combined (mostly just the latter) give a moderate speed
improvement to this hot loop.

name           old time/op    new time/op    delta
CodeEncoder-4    6.01ms ± 1%    5.91ms ± 1%  -1.66%  (p=0.002 n=6+6)

name           old speed      new speed      delta
CodeEncoder-4   323MB/s ± 1%   328MB/s ± 1%  +1.69%  (p=0.002 n=6+6)

Updates #5683.

Change-Id: I12757c325a68abb2856026cf719c122612a1f38e
Reviewed-on: https://go-review.googlesource.com/125417
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: 's avatarBrad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
parent 81487266
......@@ -632,8 +632,21 @@ func (se structEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
first := true
for i := range se.fields {
f := &se.fields[i]
fv := fieldByIndex(v, f.index)
if !fv.IsValid() || f.omitEmpty && isEmptyValue(fv) {
// Find the nested struct field by following f.index.
fv := v
FieldLoop:
for _, i := range f.index {
if fv.Kind() == reflect.Ptr {
if fv.IsNil() {
continue FieldLoop
}
fv = fv.Elem()
}
fv = fv.Field(i)
}
if f.omitEmpty && isEmptyValue(fv) {
continue
}
if first {
......@@ -835,19 +848,6 @@ func isValidTag(s string) bool {
return true
}
func fieldByIndex(v reflect.Value, index []int) reflect.Value {
for _, i := range index {
if v.Kind() == reflect.Ptr {
if v.IsNil() {
return reflect.Value{}
}
v = v.Elem()
}
v = v.Field(i)
}
return v
}
func typeByIndex(t reflect.Type, index []int) reflect.Type {
for _, i := range index {
if t.Kind() == reflect.Ptr {
......
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