Re: How to cache output of the compiler aka ccache

[Simon Wright <simon@pushface.org>]

Ludovic Brenta <ludovic.brenta@insalien.org> writes:

>                                and "gnatmake -m" does minimal
> recompilation.  This really speeds things up.

We absolutely rely on this; the handwritten code is in separate proper
bodies, 99% of specs and package bodies are generated, and the only
way to change them is to change the model and re-generate.

One thing to watch out for is that when deciding whether a unit needs
to be recompiled GNAT first checks the timestamp of each dependency;
it the timestamp is different it checks the contents of the dependency
and only recompiles if there's a semantic difference.

So recreating lots of identical source will mean that the dependencies
have to be at least parsed. This can take quite a time (I think mainly
the overhead of opening/closing the files).

We had an interesting bug with 3.16a1 on Windows where compilations
ran slower if the compiler had been installed in the winter months
(outside daylight saving time) -- a feature involving the Windows
installer, I think; the timestamps in the library were all one hour
out.

-- 
Simon Wright                               100% Ada, no bugs.