Study: build times for D programs

[Jonathan M Davis]

On Thursday, July 26, 2012 00:34:07 Andrej Mitrovic wrote:
> On 7/25/12, Jonathan M Davis <jmdavisProg at gmx.com> wrote:
> > D should actually compile _faster_ if you compile everything at once -
> > certainly for smaller projects - since it then only has to lex and parse
> > each
> > module once. Incremental builds avoid having to fully compile each module
> > every time, but there's still plenty of extra lexing and parsing which
> > goes on.
> That's assuming that the lexing/parsing is the bottleneck for DMD.

Not necessarily. The point is that there's extra work that has to be done when 
compiling separately. So, whether it takes more or less time depends on how 
much other work you're avoiding by doing an incremental build. Certainly, I'd 
expect a full incremental build from scratch to take longer than one which was 
not incremental.

> For example: a full build of  WindowsAPI takes 14.6 seconds on my machine.
> But when compiling one module at a time and using parallelism it takes
> 7 seconds instead. And all it takes is a simple parallel loop.

Parallelism? How on earth do you manage that? dmd has no support for running 
on multiple threads AFAIK. Do you run multiple copies of dmd at once? 
Certainly, compiling files in parallel changes things. You've got multiple 
cores working on it at that point, so the equation is completely different.

- Jonathan M Davis