On 12/15/2017 02:10 PM, Seb wrote:
Following the discussion at https://github.com/dlang/phobos/pull/5916,
we realized that there's quite some overhead in importing some Phobos
modules. Ideally importing a Phobos module without using it, should be
cost-free (i.e. pay for what you use).
Test case: consider a file with `import std.X` and compile it with `dmd
-c -o-`.
A quick overview of the worst of the worst:
std.regex 1.03s
std.net.curl 0.28s
std.concurrency 0.23s
std.encoding 0.18s
std.zip 0.16s
std.path 0.14s
std.file 0.14s
std.mmfile 0.14s
std.datetime 0.14s
std.socket 0.12s
std.string 0.10s
std.uni 0.09s
std.process 0.05s
This following discussions have already brought a huge improvements to
its light:
https://github.com/dlang/phobos/pull/5931
Can you do a another one?
Dmitry wrote a nice PR for that, and I wrote two:
https://github.com/dlang/phobos/pull/5942
https://github.com/dlang/phobos/pull/5931
https://github.com/dlang/phobos/pull/5948
My approach has been the following:
* First I tried to clarify which module imports what by means of
replacing "import std.xxx;" with "import std.xxx : yyy, zzz, ...;" That
has been of tremendous help in assessing each module's dependency liability.
* Then I tried to figure which imports are most costly. I inserted
__EOF__ in the module at different parts and measure how long it takes
to just import that module. After a few attempts it becomes clear which
imports are heaviest.
* Then I pushed those heavy imports down where they're needed. An import
placed in a function will not be opened while that function's module
gets imported. Same goes about template types, but not structs or
classes. (That should be fixed; see Seb's comment in my last PR.)
Not only such work reduces import times, but it's illuminating for
maintenance because it represents dependencies in a simple, fine-grained
matter.
A tool (call it depend - heh) to automate that would be awesome. For
example, this run would make all imported names explicit:
depend --explicit *.d
This run would push all imports down to the innermost scope of usage:
depend --pushdown *.d
Andrei
