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49e933fc57
Before register ABI, we always pass argument in memory, and the
compiler chooses interface conversion functions solely based on
the memory layout. As long as the two types have identical memory
layout, it is fine to mix and match, e.g. convT64 takes a uint64
argument, but it can be used for things like float64 or
struct { x [4]struct{}; y int64 }.
With register ABI, those types may be passed differently, e.g.
uint64 is passed in an integer register, float64 is passed in a
floating point register, the struct above is passed in memory.
I made a few attempts in the previous CLs to try to choose the
right function based on the argument type, but none of them is
really correct.
Instead, this CL changes it to always pass the argument in the
same type the runtime expects, and do conversion before the call
in the compiler. The conversion can be no-op (e.g. a named type
to its underlying type), direct (e.g. int64 to uint64), or
through memory (e.g. *(*uint64)(unsafe.Pointer(&arg))). This way,
the front end does not need to know the ABI. (It only needs to
know how to convert types, and it already does.)
TODO: do something similar for map functions.
Change-Id: I33fc780a47c3f332b765e09b5e527f52ea1d6b5c
Reviewed-on: https://go-review.googlesource.com/c/go/+/309029
Trust: Cherry Zhang <cherryyz@google.com>
Reviewed-by: David Chase <drchase@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'.