[Help Needed] - Debugging compilation time

[H. S. Teoh]

On Fri, Oct 21, 2022 at 04:32:17PM +0000, Hipreme via Digitalmars-d-learn wrote:
> Hey guys, I have been complaining a lot of time right now from D
> compilation speed at least for my project.
> 
> I have:
> - Underused CTFE
> - Underused Templates
> - Avoided importing standard libraries
> - Created a multi module projects for better code reuse
> 
> Those are all the techniques I have tried to maintain my compilation
> times lower, yet, It still builds slow even when using the --combined
> (which does a single compiler run on dub)

Using dub immediately slows you down by at least several seconds. There
may be some options to skip the time-consuming dependency graph
resolution and network access.  But my personal preference is to use an
offline build system with less overhead.


> So, doesn't matter if all is imported at once or not, it seems the
> problem seems to be somewhere in my project which I've been unable to
> find. I wanted to show someone who is more experienced on the time
> trace from LDC to check what I've been doing wrong.

LDC generally tends to be quite a bit slower than DMD because of the
time spent in aggressive optimizations.  For development builds,
consider using DMD instead.


> This time trace took 9 seconds. DMD takes 7 seconds to build my
> project.  Adam has built his entire arsd in 2.5 seconds, while my PC
> is faster and arsd is much bigger than my project, this does not make
> any sense.

It could be caused by a number of different things:

- Using many nested templates will slow down compilation.
- Doing excessive CTFE computations will slow things down.
- Using unusually-large static arrays in some cases may trigger slow
  paths in the front-end, consuming lots of compiler memory.
- Using string imports may slow things down as the compiler parses the
  imported file(s).
- Having excessively-large function bodies may trigger some O(n^2) paths
  in the compiler that significantly slows things down.
- Using excessive mixins may also slow things down due to copying of the
  AST.

OTOH, uninstantiated templates are cheap (the only cost is parsing them,
which is very fast): just avoiding templates along may not save you much
time if it's being spent elsewhere.  I suspect a good chunk of Adam's
code is in uninstantiated templates, so a straight comparison isn't
really fair, if those templates aren't actually being instantiated in
the first place.

I also notice you use mixin templates a lot; it might be worth
investigating whether they might be the cause of your issue.


> So I would gladly wish you guys help:
> 
> My repository: https://github.com/MrcSnm/HipremeEngine/
> My time trace: https://ufile.io/gmvw1wlu (This time trace will be in air for
> 30 days only)

Sorry, no time to look into it in detail, but I did skim over a few
files and note that you use mixin templates a lot.  I haven't had much
experience with mixin templates but it might be worth investigating
whether they might be causing compile time slowdowns.


T

-- 
They say that "guns don't kill people, people kill people." Well I think the gun helps. If you just stood there and yelled BANG, I don't think you'd kill too many people. -- Eddie Izzard, Dressed to Kill