commit 82760ceffaa2541f404cd14beb6cb35bf0d38c3c
author Joe Tsai <joetsai@digital-static.net> Thu Jun 20 03:09:57 2019 -0700
committer Joe Tsai <joetsai@digital-static.net> Wed Jul 10 19:44:24 2019 +0000
tree 7b1df2cbebde6e5f381ee039f655d73befe79701
parent 36dc22ddb8a46ab2f11cba079cc1192a5d4660a3

internal/impl: add MessageState to every generated message

We define MessageState, which is essentially an atomically set *MessageInfo.
By nesting this as the first field in every generated message, we can
implement the reflective methods on a *MessageState when obtained by
unsafe casting a concrete message pointer as a *MessageState.
The MessageInfo held by MessageState provides additional Go type information
to interpret the memory that comes after the contents of the MessageState.

Since we are nesting a MessageState in every message,
the memory use of every message instance grows by 8B.

On average, the body of ProtoReflect grows from 133B to 202B (+50%).
However, this is offset by XXX_Methods, which is 108B and
will be removed in a future CL. Taking into account the eventual removal
of XXX_Methods, this is a net reduction of 25%.

name          old time/op    new time/op    delta
Name/Value-4    70.3ns ± 2%    17.5ns ± 6%   -75.08%  (p=0.000 n=10+10)
Name/Nil-4      70.6ns ± 3%    33.4ns ± 2%   -52.66%  (p=0.000 n=10+10)

name          old alloc/op   new alloc/op   delta
Name/Value-4     16.0B ± 0%      0.0B       -100.00%  (p=0.000 n=10+10)
Name/Nil-4       16.0B ± 0%      0.0B       -100.00%  (p=0.000 n=10+10)

name          old allocs/op  new allocs/op  delta
Name/Value-4      1.00 ± 0%      0.00       -100.00%  (p=0.000 n=10+10)
Name/Nil-4        1.00 ± 0%      0.00       -100.00%  (p=0.000 n=10+10)

Change-Id: I92bd58dc681c57c92612fd5ba7fc066aea34e95a
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/185460
Reviewed-by: Damien Neil <dneil@google.com>