[Qt-creator] clangd parsing time

Adam Light aclight at gmail.com
Wed Dec 1 17:32:28 CET 2021

On Wed, Dec 1, 2021 at 1:59 AM Eike Ziller <Eike.Ziller at qt.io> wrote:

> Hi,
> I have got a fix for macOS (in LLVM), and a similar patch that _might_
> improve things on Windows too
> https://codereview.qt-project.org/c/clang/llvm-project/+/382042
> but since we fail to reproduce the huge difference between "compiling" and
> "clangd indexing" that you observe in the first place, we have a difficult
> time verifying that this indeed helps.
> We have created a build of clangd with the potential fix and I've uploaded
> it here:
> https://download.qt.io/development_releases/prebuilt/libclang/testing/
> it would be great if you could test if this improves things for you. Set
> the path to the new clangd in Tools > Options > C++ > Clangd > Path to
> executable.
I gave that a try, and after deleting my build directory it still took a
very long time for clangd to completely parse my project. Today it took 2
hours 44 minutes. Previously, with the clangd.exe that shipped with QtC
6.0.0-beta1, it took 3 hours 54 minutes. So today's run was substantially
faster, but still orders of magnitude greater than the ~2 minutes it takes
to fully build the same project on the same machine.

For what it's worth, I had noticed that sometimes clangd can parse the
project substantially faster (this was using clangd.exe that shipped with
6.0.0-beta1 and/or beta2). I first noticed this after I added clangd.exe to
the list of processes that Windows Defender should ignore. After adding
this exclusion, parsing was done in about an hour (I didn't precisely time
it). But then I tried deleting the build directory and re-parsing yet again
and that time it took many hours (again, not with precise timing). I tried
fiddling around with various system settings, etc. and could not figure out
what was causing the difference in parsing speed. So while today's test
with the new clangd.exe was substantially faster than the previous test, I
would not put much confidence in this difference being due to clangd.exe

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