tree e168be1cd0f1fcc34019feb4fae4005084d48957
parent d0b074956d6ea3b5a4d5b4b6b0ccce0900c44af6
author Damien Neil <dneil@google.com> 1576611557 -0800
committer Damien Neil <dneil@google.com> 1576620857 +0000

internal/impl: faster map fast path

Avoid using protobuf reflection on map values in the fast path. Range
operations in particular are expensive in protoreflect, because the
closure passed to Map.Range escapes.

Iterate maps using a reflect.MapIter when available.

When operating on maps of messages where we have a *MessageInfo for the
message type, directly jump to the fast-path *MessageInfo methods rather
than passing through the proto package.

Benchmarks deltas for a google.protobuf.Struct with JSON represention:
  {"parameters":{"a":{"b":{"c":{"d":{"e":{"f":{"g":{}}}}}}}}}

Compared to previous revision:

  name                      old time/op  new time/op  delta
  NestedStruct/Size         7.22µs ± 2%  4.84µs ± 2%  -32.96%  (p=0.000 n=8+8)
  NestedStruct/Size-8       9.30µs ± 2%  5.89µs ± 2%  -36.60%  (p=0.000 n=8+8)
  NestedStruct/Marshal      77.6µs ±12%   9.8µs ± 4%  -87.33%  (p=0.000 n=8+8)
  NestedStruct/Marshal-8    91.6µs ± 2%  11.9µs ± 2%  -86.99%  (p=0.000 n=8+8)
  NestedStruct/Unmarshal    11.5µs ± 4%   8.7µs ± 2%  -24.76%  (p=0.000 n=8+8)
  NestedStruct/Unmarshal-8  15.4µs ± 4%  11.9µs ± 2%  -22.41%  (p=0.000 n=8+8)

Compared to github.com/golang/protobuf:

  name                      old time/op  new time/op  delta
  NestedStruct/Size         5.42µs ± 1%  4.84µs ± 2%  -10.61%  (p=0.000 n=8+8)
  NestedStruct/Size-8       6.34µs ± 2%  5.89µs ± 2%   -7.10%  (p=0.000 n=8+8)
  NestedStruct/Marshal      12.5µs ± 2%   9.8µs ± 4%  -21.41%  (p=0.000 n=7+8)
  NestedStruct/Marshal-8    14.1µs ± 3%  11.9µs ± 2%  -15.52%  (p=0.000 n=8+8)
  NestedStruct/Unmarshal    9.66µs ± 1%  8.65µs ± 2%  -10.40%  (p=0.000 n=7+8)
  NestedStruct/Unmarshal-8  11.7µs ± 3%  11.9µs ± 2%   +1.95%  (p=0.038 n=8+8)

Change-Id: I0effe6491f30d41f31904777f74eca3ac3694db3
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/211737
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>