[Qbs] QBS script parsing speed

[Richard Weickelt]

Jochen,

>> Well [the time] goes into "Handling Products". So it is ModuleLoader::handleProduct().
>> And there, it could be the ModuleMerger. But speculation is dangerous when discussing about performance.
> See https://lists.qt-project.org/pipermail/qbs/2019-August/002546.html
> 
> You can find my test results together with the scripts to generate the projects here:
> https://gist.github.com/j-ulrich/35f345007809c77403a8ee88f4d9db11#file-results-md

Then you might be happy to hear that the ModuleMerger was completely
rewritten for Qbs 1.16.0
(https://codereview.qt-project.org/c/qbs/qbs/+/284737). Running your
benchmark with Qbs 1.16.0 (Qt Creator 4.12) gives me significantly better
results in case of transitive dependencies. See below.

I am not sure whether this has any noticable effect on real-world projects.
But if ModuleMerger was ever a bottleneck, then it should not longer be.

---------------------
i5-2520M CPU @ 2.50GHz Xubuntu 16.04)
First line: Qbs 1.15.1
Second line: Qbs 1.16.0

> Resolving 4-8-direct
real    0m3.089s
real    0m2.669s

> Resolving 4-8-implicit
real    0m4.808s
real    0m3.409s

> Resolving 4-8-explicit
real    0m3.898s
real    0m3.085s

> Resolving withLeafExports/4-8-direct
real    0m16.508s
real    0m13.793s

> Resolving withLeafExports/4-8-implicit
real    0m25.907s
real    0m18.180s

> Resolving withLeafExports/4-8-explicit
real    0m21.393s
real    0m15.844s

> Resolving withLeafExports/9-2-direct
real    0m13.992s
real    0m10.750s

> Resolving withLeafExports/9-2-implicit
real    0m43.592s
real    0m24.494s

> Resolving withLeafExports/9-2-explicit
real    0m26.019s
real    0m17.589s

> Resolving withAdditionalDepends/4-8-direct
real    0m25.096s
real    0m18.892s

> Resolving withAdditionalDepends/4-8-implicit
real    0m28.369s
real    0m19.868s

> Resolving withAdditionalDepends/4-8-explicit
real    0m29.164s
real    0m19.319s

> Resolving withAdditionalDepends/9-2-direct
real    0m19.110s
real    0m17.264s

> Resolving withAdditionalDepends/9-2-implicit
real    0m20.887s
real    0m19.269s

> Resolving withAdditionalDepends/9-2-explicit
real    0m18.359s
real    0m18.149s

> Resolving 9-2-direct
real    0m2.500s

> Resolving 9-2-implicit
real    0m6.393s

> Resolving 9-2-explicit
real    0m3.833s
real    0m2.326s