I have recently been reviewing ways to improve build times for our project,
which is comprised of a number of static libraries. I stumbled across this post
on the CMake tracker from 2012/13 (https://cmake.org/Bug/view.php?id=13799
<https://cmake.org/Bug/view.php?id=13799>). It suggests adding a
COMPILE_DEPENDS target property to to explicitly set dependencies for STATIC
libraries instead of always using all linked libraries as build-order
dependencies.
Having done a draft implementation in a local CMake repository it has shaved
off 20% of our 120s build time. I expect the savings to be much more dramatic
when I test with Incredibuild (approximately 50% based on tests done previously
from just deleting dependencies manually in Visual Studio).
I don’t really want to refactor our code to use “OBJECT” libraries as the
inability to link with other targets means that propagating compile options /
include directories etc down the chain of linked libs becomes painful. This
method allows me to switch between static and shared libs using a config option
and none of my CMake scripts need to change.
Anyway, I was wondering whether there was any interest in me pushing my
solution back to Git / submitting a Pull request so that it might be merged in
at some point. If there is - any advice on any gotchas I might watch for
instead of just adding some fairly simple code to cmComputeTargetDepends.cxx
would be gratefully received - especially as this is my first time poking
around in CMake code.
// John Wordsworth
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