encoding/json: remove allocation when using a Marshaler with value receiver
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 <mvdan@mvdan.cc>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>