Edits inside a function can cause a big increase in IntelliSense update time

[sean-mcmanus]

I have a repro with 3.2k functions that each calls another function (generated with the help of Copilot), and after just 4 edits it starts taking around 8 times as long to update the TU. I don't repro the same behavior in VS. The processing time goes down to the original update time after a save.

It seems to repro for all TUs in general after enough edits are made, but the particular repro case seems like a "worst case" for some reason.

[heartacker]

yes. slow here

[sean-mcmanus]

It repros in VS too if no save, edit with ; or }, replace/rename edit, or document/window switch occurs. The only difference compared to VS is that we don't trigger an IntelliSense update with a preparse if the document switches from a non-C++ file and back (which we used to be prior to 1.5 in June 2021) or from a different app window and back (which we never implemented, i.e. via handling onWindowStateChanged).

i.e. it seems like this performance issue would only occur if the user were making a lot of modification edits to a large TU with lots of definitions, such as adding comments. UPDATE: Actually, it's also fixed when the cursor moves to a new line, i.e. modifications to different lines won't repro the issue.

UPDATE: Modifications or cursor changes inside a function don't free the memory, but a save will still (even though it doesn't in VS).

I filed a VS bug for the "in function" memory accumulation (and update slowdown) on edits: https://developercommunity.visualstudio.com/t/C-IntelliSense-memory-usage-and-update/10817292 .

This issue is tracking multiple issues so it might need to be split into separate issues if only a subset of issues is fixed.