code review 103700043: encoding/gob: simplify allocation in decode.

encoding/gob: simplify allocation in decode.
The old code's structure needed to track indirections because of the
use of unsafe. That is no longer necessary, so we can remove all
that tracking. The code cleans up considerably but is a little slower.
We may be able to recover that performance drop. I believe the
code quality improvement is worthwhile regardless.

BenchmarkEndToEndPipe           5610          5780          +3.03%
BenchmarkEndToEndByteBuffer     3156          3222          +2.09%

[r, 2014-06-30 21:50:14]

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

I'd like you to review this change to
https://code.google.com/p/go

[rsc, 2014-06-30 22:03:41]

LGTM

https://codereview.appspot.com/103700043/diff/1/src/pkg/encoding/gob/decode.go
File src/pkg/encoding/gob/decode.go (right):

https://codereview.appspot.com/103700043/diff/1/src/pkg/encoding/gob/decode.g...
src/pkg/encoding/gob/decode.go:145: func decIndirect(pv reflect.Value)
reflect.Value {
This is now the same as decAlloc.
More to the point, decIndirect used to do the first N-1 allocations and decAlloc
the last.
Now that both can do all of them, one can go away.
I suggest dropping the calls to decIndirect and deleting this function,
although perhaps decAlloc should be the one to go (whichever works).

[r, 2014-06-30 22:43:25]

Nice idea. Removing decIndirect also recovers almost half of the performance
drop.

[r, 2014-06-30 22:47:14]

*** Submitted as https://code.google.com/p/go/source/detail?r=c31a70f2f542 ***

encoding/gob: simplify allocation in decode.
The old code's structure needed to track indirections because of the
use of unsafe. That is no longer necessary, so we can remove all
that tracking. The code cleans up considerably but is a little slower.
We may be able to recover that performance drop. I believe the
code quality improvement is worthwhile regardless.

BenchmarkEndToEndPipe           5610          5780          +3.03%
BenchmarkEndToEndByteBuffer     3156          3222          +2.09%

LGTM=rsc
R=rsc
CC=golang-codereviews
https://codereview.appspot.com/103700043

[dave_cheney.net, 2014-07-01 12:53:28]

https://codereview.appspot.com/103700043/diff/20001/src/pkg/encoding/gob/deco...
File src/pkg/encoding/gob/decode.go (right):

https://codereview.appspot.com/103700043/diff/20001/src/pkg/encoding/gob/deco...
src/pkg/encoding/gob/decode.go:380: //	println(value.Kind() == reflect.Ptr)
left over debugging.