4f97ec0866
In particular, we can initialize globals with them at link time instead of generating code for them in an init() function. Less code, less startup cost. But the real reason for this change is binary size. This change reduces the binary size of hello world by ~4%. The culprit is fmt.ssFree, a global variable which is a sync.Pool of scratch scan states. It is initalized with a captureless closure as the pool's New action. That action in turn references all the scanf code. If you never call any of the fmt.Scanf* routines, ssFree is never used. But before this change, ssFree is still referenced by fmt's init function. That keeps ssFree and all the code it references in the binary. With this change, ssFree is initialized at link time. As a result, fmt.init never mentions ssFree. If you don't call fmt.Scanf*, ssFree is unreferenced and it and the scanf code are not included. This change is an easy fix for what is generally a much harder problem, the unnecessary initializing of unused globals (and retention of code that they reference). Ideally we should have separate init code for each global and only include that code if the corresponding global is live. (We'd need to make sure that the initializing code has no side effects, except on the global being initialized.) That is a much harder change. Update #6853 Change-Id: I19d1e33992287882c83efea6ce113b7cfc504b67 Reviewed-on: https://go-review.googlesource.com/17398 Reviewed-by: Russ Cox <rsc@golang.org> Run-TryBot: Russ Cox <rsc@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> |
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Binary Distribution Notes
If you have just untarred a binary Go distribution, you need to set the environment variable $GOROOT to the full path of the go directory (the one containing this file). You can omit the variable if you unpack it into /usr/local/go, or if you rebuild from sources by running all.bash (see doc/install-source.html). You should also add the Go binary directory $GOROOT/bin to your shell's path.
For example, if you extracted the tar file into $HOME/go, you might put the following in your .profile:
export GOROOT=$HOME/go
export PATH=$PATH:$GOROOT/bin
See https://golang.org/doc/install or doc/install.html for more details.