Hi Thiago,

On Feb 5, 2014, at 6:18 PM, Thiago Macieira <[email protected]> wrote:

> Em qua 05 fev 2014, às 11:58:50, Simon Hausmann escreveu:
> 
> I'm with Simon, this is very interesting stuff!

Thank you! :-)

> I'm wondering if we could make use of your data to figure out what headers we 
> should precompile.

This is a fascinating idea actually. We primarily motivate our work based on 
refactoring, but as you mentioned, some really hot files just cannot be 
refactored due to architectural concerns. Perhaps precompiling the hot headers 
is another way these hotspots can be addressed.

> You said you extract a graph from the build: is there a way 
> to parse that graph to produce a list of headers most commonly included in a 
> given module?

Yes, this should be possible. Within our graph, each header file is a node that 
is connected by an edge to each object file (another node) that needs to be 
recompiled when the header changes. A simple measure like the sum of all the 
edges coming out of a header file will tell you how many objects are recompiled 
when it changes, which is a kind of proxy for the number of files including a 
header.

> We've had precompilation support in qmake for a decade, but apparently we use 
> that in exactly 3 modules...

Hmm, it could also be interesting to look into these modules to see if having 
them precompiled is justified by its hotness?

Kind regards,
-Shane
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