On Wednesday, 20 December 2017 at 18:21:33 UTC, Andrei
Alexandrescu wrote:
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
I'm on it. I tried using a version of Seb's frontend library
yesterday but with the standard dmd main and tried running it on
std.stdio, but it asserted in asmSemantic because of an asm block
somewhere in druntime, so I'm back to using a tweaked full dmd
with the backend simply disabled again:
https://github.com/dlang/dmd/pull/7425
https://github.com/dlang/dmd/blob/master/src/dmd/gluelayer.d#L47
https://gist.github.com/joakim-noah/09cf49bee3d82b03a54f
Once I have something basic working, I'll put it up on github, so
others who are interested can play with it and pitch in to make
it a real tool.
