code review 6946059: encoding/json: cleanup leftover redundant variables.

encoding/json: cleanup leftover redundant variables.

Those variables come from ancient times when reflect.Value was
an interface.

[remyoudompheng, 2012-12-15 09:39:59]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://go.googlecode.com/hg/

[dave_cheney.net, 2012-12-15 09:50:39]

Looks like there is a small reduction in stack usage

linux/amd64

before:
0214 (/home/dfc/go/src/pkg/encoding/json/decode.go:117) TEXT   
(*decodeState).unmarshal+0(SB),$136-40

after:
0214 (/home/dfc/go/src/pkg/encoding/json/decode.go:117) TEXT   
(*decodeState).unmarshal+0(SB),$112-40

Any improvements in the go1 benchmarks ?

[remyoudompheng, 2012-12-15 16:49:10]

On 2012/12/15 09:50:39, dfc wrote:
> Looks like there is a small reduction in stack usage
> 
> linux/amd64
> 
> before:
> 0214 (/home/dfc/go/src/pkg/encoding/json/decode.go:117) TEXT   
> (*decodeState).unmarshal+0(SB),$136-40
> 
> after:
> 0214 (/home/dfc/go/src/pkg/encoding/json/decode.go:117) TEXT   
> (*decodeState).unmarshal+0(SB),$112-40
> 
> Any improvements in the go1 benchmarks ?

There may be a little improvement but it's hard to detect.

[dave_cheney.net, 2012-12-16 05:02:37]

> There may be a little improvement but it's hard to detect.

A small speedup in the encoding/json benchmarks

loco(~/go/src/pkg/encoding/json) % ~/go/misc/benchcmp {old,new}.txt
benchmark                      old ns/op    new ns/op    delta
BenchmarkCodeEncoder           979094200    959876800   -1.96%
BenchmarkCodeMarshal           993980000    976984200   -1.71%
BenchmarkCodeDecoder          2147483647   2147483647  -10.30%
BenchmarkCodeUnmarshal        2147483647   2147483647  -10.65%
BenchmarkCodeUnmarshalReuse   2147483647   2147483647  -10.37%
BenchmarkSkipValue            2147483647   2147483647   -0.95%

benchmark                       old MB/s     new MB/s  speedup
BenchmarkCodeEncoder                1.98         2.02    1.02x
BenchmarkCodeMarshal                1.95         1.99    1.02x
BenchmarkCodeDecoder                0.78         0.87    1.12x
BenchmarkCodeUnmarshal              0.80         0.90    1.12x
BenchmarkCodeUnmarshalReuse         0.80         0.89    1.11x
BenchmarkSkipValue                  0.14         0.14    1.00x

[dave_cheney.net, 2012-12-16 06:32:09]

oops, those numbers were low due to issue 4557. Here are the correct numbers

loco(~/go/src/pkg/encoding/json) % ~/go/misc/benchcmp {old,new}.txt
benchmark                      old ns/op    new ns/op    delta
BenchmarkCodeEncoder           848969600    842224200   -0.79%
BenchmarkCodeMarshal           854402800    839645600   -1.73%
BenchmarkCodeDecoder          2147483647   2068182000   -9.79%
BenchmarkCodeUnmarshal        2147483647   1976916000  -11.11%
BenchmarkCodeUnmarshalReuse   2147483647   1990444000  -11.08%
BenchmarkSkipValue            2147483647   2147483647   -0.79%

benchmark                       old MB/s     new MB/s  speedup
BenchmarkCodeEncoder                2.29         2.30    1.00x
BenchmarkCodeMarshal                2.27         2.31    1.02x
BenchmarkCodeDecoder                0.85         0.94    1.11x
BenchmarkCodeUnmarshal              0.87         0.98    1.13x
BenchmarkCodeUnmarshalReuse         0.87         0.97    1.11x
BenchmarkSkipValue                  0.61         0.62    1.02x

[rsc, 2012-12-17 00:35:41]

LGTM

[remyoudompheng, 2012-12-17 01:35:15]

*** Submitted as https://code.google.com/p/go/source/detail?r=5083a8d8cc89 ***

encoding/json: cleanup leftover redundant variables.

Those variables come from ancient times when reflect.Value was
an interface.

R=dave, rsc
CC=golang-dev
https://codereview.appspot.com/6946059