From b80f7823297d263ec6ceb70e44a9c6b2073c1b3c Mon Sep 17 00:00:00 2001 From: Phil Pearl Date: Sun, 27 Oct 2019 16:05:54 +0000 Subject: [PATCH] encoding/json: remove allocation when using a Marshaler with value receiver MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit If we marshal a non-pointer struct field whose type implements Marshaler with a non-pointer receiver, then we avoid an allocation if we take the address of the field before casting it to an interface. name old time/op new time/op delta EncodeMarshaler-8 104ns ± 1% 92ns ± 2% -11.72% (p=0.001 n=7+7) name old alloc/op new alloc/op delta EncodeMarshaler-8 36.0B ± 0% 4.0B ± 0% -88.89% (p=0.000 n=8+8) name old allocs/op new allocs/op delta EncodeMarshaler-8 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.000 n=8+8) Test coverage already looks good enough for this change. TestRefValMarshal already covers all possible combinations of value & pointer receivers on value and pointer struct fields. Change-Id: I6fc7f72396396d98f9a90c3c86e813690f41c099 Reviewed-on: https://go-review.googlesource.com/c/go/+/203608 Reviewed-by: Daniel Martí Run-TryBot: Daniel Martí TryBot-Result: Gobot Gobot --- encode.go | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/encode.go b/encode.go index a7473a7..b81e505 100644 --- a/encode.go +++ b/encode.go @@ -399,19 +399,22 @@ var ( // newTypeEncoder constructs an encoderFunc for a type. // The returned encoder only checks CanAddr when allowAddr is true. func newTypeEncoder(t reflect.Type, allowAddr bool) encoderFunc { - if t.Implements(marshalerType) { - return marshalerEncoder - } + // If we have a non-pointer value whose type implements + // Marshaler with a value receiver, then we're better off taking + // the address of the value - otherwise we end up with an + // allocation as we cast the value to an interface. if t.Kind() != reflect.Ptr && allowAddr && reflect.PtrTo(t).Implements(marshalerType) { return newCondAddrEncoder(addrMarshalerEncoder, newTypeEncoder(t, false)) } - - if t.Implements(textMarshalerType) { - return textMarshalerEncoder + if t.Implements(marshalerType) { + return marshalerEncoder } if t.Kind() != reflect.Ptr && allowAddr && reflect.PtrTo(t).Implements(textMarshalerType) { return newCondAddrEncoder(addrTextMarshalerEncoder, newTypeEncoder(t, false)) } + if t.Implements(textMarshalerType) { + return textMarshalerEncoder + } switch t.Kind() { case reflect.Bool: