Noticed in profiles that invoking *VoteSignBytes always created a
bytes.Buffer, then discarded it inside protoio.MarshalDelimited.
I dug further and examined the call paths and noticed that we
unconditionally create the bytes.Buffer, even though we might
have proto messages (in the common case) that implement
MarshalTo([]byte), and invoked varintWriter. Instead by inlining
this case, we skip a bunch of allocations and CPU cycles,
which then reflects properly on all calling functions. Here
are the benchmark results:
```shell
$ benchstat before.txt after.txt
name old time/op new time/op delta
types.VoteSignBytes-8 705ns ± 3% 573ns ± 6% -18.74% (p=0.000 n=18+20)
types.CommitVoteSignBytes-8 8.15µs ± 9% 6.81µs ± 4% -16.51% (p=0.000 n=20+19)
protoio.MarshalDelimitedWithMarshalTo-8 788ns ± 8% 772ns ± 3% -2.01% (p=0.050 n=20+20)
protoio.MarshalDelimitedNoMarshalTo-8 989ns ± 4% 845ns ± 2% -14.51% (p=0.000 n=20+18)
name old alloc/op new alloc/op delta
types.VoteSignBytes-8 792B ± 0% 600B ± 0% -24.24% (p=0.000 n=20+20)
types.CommitVoteSignBytes-8 9.52kB ± 0% 7.60kB ± 0% -20.17% (p=0.000 n=20+20)
protoio.MarshalDelimitedNoMarshalTo-8 808B ± 0% 440B ± 0% -45.54% (p=0.000 n=20+20)
name old allocs/op new allocs/op delta
types.VoteSignBytes-8 13.0 ± 0% 10.0 ± 0% -23.08% (p=0.000 n=20+20)
types.CommitVoteSignBytes-8 140 ± 0% 110 ± 0% -21.43% (p=0.000 n=20+20)
protoio.MarshalDelimitedNoMarshalTo-8 10.0 ± 0% 7.0 ± 0% -30.00% (p=0.000 n=20+20)
```
Thanks to Tharsis who tasked me to help them increase TPS and who
are keen on improving Tendermint and efficiency.
Emmanuel T Odeke
3e92899bd9