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Robert Findley ddd8bc1b07 go/types, types2: optimize instance lookup in LookupFieldOrMethod
LookupFieldOrMethod appears as a hotspot when benchmarking gopls'
auto-completion. In particular, instanceLookup.add was allocating in the
common case of structs with no embedding.

This is easily fixed, by using a small array in front of the map inside
of instanceLookup. Do this, and additionally add a microbenchmark.

The benchmark improvement is significant:

name                    old time/op    new time/op    delta
LookupFieldOrMethod-12     388µs ± 6%     154µs ± 3%  -60.36%  (p=0.000 n=10+10)

name                    old alloc/op   new alloc/op   delta
LookupFieldOrMethod-12     152kB ± 0%       2kB ± 0%  -98.77%  (p=0.000 n=9+10)

name                    old allocs/op  new allocs/op  delta
LookupFieldOrMethod-12     1.41k ± 0%     0.07k ± 0%  -95.38%  (p=0.000 n=10+10)

It should also be noted that instanceLookup is used elsewhere, in
particular by validType. In those contexts, the scope is not just the
current type but the entire package, and so the newly added buffer is
likely to simply cause extra Identical checks. Nevertheless, those
checks are cheap, and on balance the improved LookupFieldOrMethod
performance leads overall to improved type-checking performance.
Standard library benchmark results varied by package, but type checking
speed for many packages improved by ~5%, with allocations improved by
~10%. If this weren't the case we could let the caller control the
buffer size, but that optimization doesn't seem necessary at this time.

For example:

Check/http/funcbodies/noinfo-12            71.5ms ± 4%    67.3ms ± 2%   -5.90%  (p=0.000 n=20+20)
Check/http/funcbodies/noinfo-12              244k ± 0%      219k ± 0%  -10.36%  (p=0.000 n=19+19)

Updates golang/go#53992

Change-Id: I10b6deb3819ab562dbbe1913f12b977cf956dd50
Reviewed-on: https://go-review.googlesource.com/c/go/+/423935
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
2022-10-13 15:31:35 +00:00
.github .github: update issue label for pkgsite-removal 2022-09-07 16:00:20 +00:00
api runtime/coverage: revise/shorten function names 2022-10-05 14:59:05 +00:00
doc spec: describe an edge case for slice expression of nil slice 2022-09-21 14:06:17 +00:00
lib/time lib/time, time/tzdata: update to 2022b 2022-08-11 20:03:19 +00:00
misc misc/cgo/test: add asan and msan arena tests 2022-10-12 20:44:43 +00:00
src go/types, types2: optimize instance lookup in LookupFieldOrMethod 2022-10-13 15:31:35 +00:00
test test: update test/run.go and some tests to use importcfg 2022-10-12 23:16:41 +00:00
.gitattributes all: treat all files as binary, but check in .bat with CRLF 2020-06-08 15:31:43 +00:00
.gitignore internal/buildcfg: move build configuration out of cmd/internal/objabi 2021-04-16 19:20:53 +00:00
codereview.cfg codereview.cfg: add codereview.cfg for master branch 2021-02-19 18:44:53 +00:00
CONTRIBUTING.md
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README.md README.md: update wiki link 2022-04-26 16:21:18 +00:00
SECURITY.md SECURITY.md: replace golang.org with go.dev 2022-04-26 19:59:47 +00:00

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