CodeQL version 2.18.2 doubles the amount of time spent compiling CodeQL databases

[flowerhack]

Hi there,

I'm a committer for the Chromium project & we've been experimenting with building CodeQL databases of Chromium.

Recently, we upgraded the version of CodeQL we were using to compile our databases from 2.18.1 to 2.18.2, so we could include some fixes y'all have recently merged for bugs Chromium ran into (thank you!).

However, we noticed a huge spike in the time it takes to build a CodeQL database after making this switch—it increased the build time by ~2x (and in particular some of our builders started timing out).

We can increase builder timeouts if need be, but we'd like to understand if there's some more fundamental problem here (and if so, is it specific to Chromium or has it been seen on other projects, etc), or if that sharp of an increase in build time is considered a bug.

If it's useful for your analysis, you can view our builder here: https://ci.chromium.org/ui/p/chromium/builders/ci/linux-codeql-generator. The purple failing builds started occuring around 2331, which is when we made the version switch, and started working again at 2337 when we switched the version back.

You'll notice, if you expand out the steps, that the time on the index_target.py step is what is particularly taking longer. That step is primarily a wrapper around the commands to compile the CodeQL database; you can view the script here in case that's useful.

I see that 2.18.3 is now available; I may try to update with that version number, in case this was a known bug that was fixed in the very next version, but I'm reporting this now on the assumption that that's not the case.

Thanks for any help you can offer!