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ddd8bc1b07
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> |
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Vendoring in std and cmd
========================
The Go command maintains copies of external packages needed by the
standard library in the src/vendor and src/cmd/vendor directories.
In GOPATH mode, imports of vendored packages are resolved to these
directories following normal vendor directory logic
(see golang.org/s/go15vendor).
In module mode, std and cmd are modules (defined in src/go.mod and
src/cmd/go.mod). When a package outside std or cmd is imported
by a package inside std or cmd, the import path is interpreted
as if it had a "vendor/" prefix. For example, within "crypto/tls",
an import of "golang.org/x/crypto/cryptobyte" resolves to
"vendor/golang.org/x/crypto/cryptobyte". When a package with the
same path is imported from a package outside std or cmd, it will
be resolved normally. Consequently, a binary may be built with two
copies of a package at different versions if the package is
imported normally and vendored by the standard library.
Vendored packages are internally renamed with a "vendor/" prefix
to preserve the invariant that all packages have distinct paths.
This is necessary to avoid compiler and linker conflicts. Adding
a "vendor/" prefix also maintains the invariant that standard
library packages begin with a dotless path element.
The module requirements of std and cmd do not influence version
selection in other modules. They are only considered when running
module commands like 'go get' and 'go mod vendor' from a directory
in GOROOT/src.
Maintaining vendor directories
==============================
Before updating vendor directories, ensure that module mode is enabled.
Make sure GO111MODULE=off is not set ('on' or 'auto' should work).
Requirements may be added, updated, and removed with 'go get'.
The vendor directory may be updated with 'go mod vendor'.
A typical sequence might be:
cd src
go get -d golang.org/x/net@latest
go mod tidy
go mod vendor
Use caution when passing '-u' to 'go get'. The '-u' flag updates
modules providing all transitively imported packages, not only
the module providing the target package.
Note that 'go mod vendor' only copies packages that are transitively
imported by packages in the current module. If a new package is needed,
it should be imported before running 'go mod vendor'.