tree 9545c63ae959f745e932c352e2c05f151cbc4e8a
parent 8525b20428fdd941303fbebd0e1b1e43dd5f286a
author Joe Tsai <joetsai@digital-static.net> 1588923126 -0700
committer Joe Tsai <joetsai@digital-static.net> 1589340614 +0000

internal/impl: avoid inlining fixed coderFieldInfo array

Any attempt at guessing the size for a fixed coderFieldInfo array
will always get it wrong in some cases, either by under-estimating
or over-estimating the count. The former causes worse caching behavior,
while the latter causes memory waste.

As a middle ground, just pre-allocate a slice of the exact length.
Each element will have memory locality with each other, but not
be guaranteed to have memory locality with the parent coderMessageInfo.

name                            old time/op  new time/op  delta
EmptyMessage/Wire/Marshal-8     43.1ns ±11%  42.6ns ± 8%  -1.32%  (p=0.036 n=50+49)
EmptyMessage/Wire/Unmarshal-8   18.6ns ±10%  18.9ns ±12%    ~     (p=0.054 n=50+50)
EmptyMessage/Wire/Validate-8    15.0ns ± 9%  14.7ns ±10%  -2.44%  (p=0.002 n=50+45)
EmptyMessage/Clone-8             163ns ±20%   149ns ±19%  -8.58%  (p=0.000 n=48+53)
RepeatedInt32/Wire/Marshal-8    4.27µs ±12%  4.24µs ±13%    ~     (p=0.612 n=48+52)
RepeatedInt32/Wire/Unmarshal-8  3.47µs ±14%  3.50µs ±11%    ~     (p=0.217 n=50+53)
RepeatedInt32/Wire/Validate-8   2.12µs ±12%  2.09µs ± 9%    ~     (p=0.121 n=50+51)
RepeatedInt32/Clone-8           3.04µs ±18%  2.98µs ±36%    ~     (p=0.289 n=51+54)
Required/Wire/Marshal-8          281ns ±14%   276ns ±11%    ~     (p=0.059 n=48+55)
Required/Wire/Unmarshal-8        117ns ±14%   118ns ±11%    ~     (p=0.358 n=49+53)
Required/Wire/Validate-8        87.6ns ± 9%  88.0ns ±12%    ~     (p=0.373 n=48+53)
Required/Clone-8                 533ns ±12%   507ns ±15%  -4.71%  (p=0.000 n=49+54)

Change-Id: I4cf3134e424130bee728b7591127e5c80f07e2db
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/232937
Reviewed-by: Damien Neil <dneil@google.com>