Might Qt subsystem initialization time depend on compiler optimization level?

Andreas Schacherbauer

Hi,
Could it be that Qt subsystem initialization (font rendering for example) performance depend on the compiler optimization level that was used during the Qt build?
Or are there other ways to improve the performance of e.g. setting up font rendering?

I'm asking this because we have a binary that was build with an older version of Qt (probably 5.10.x) which initializes font rendering 4x faster then if we build the same version of Qt ourselves.

Best regards,
Andi

kshegunov

@Andreas-Schacherbauer said in Might Qt subsystem initialization time depend on compiler optimization level?:

Could it be that Qt subsystem initialization (font rendering for example) performance depend on the compiler optimization level that was used during the Qt build?

Absolutely.

Or are there other ways to improve the performance of e.g. setting up font rendering?

For production use the most optimized build you can muster.*
For development, you might want to have a debug build.

I'm asking this because we have a binary that was build with an older version of Qt (probably 5.10.x) which initializes font rendering 4x faster then if we build the same version of Qt ourselves.

Is it the same compiler? Do you enable the same sort of optimizations? For example, do you see -march=native or -mavx2 or stuff like this? It may very well be that the prebuilt version is well optimized for the hardware, while yours may not be.

* Except in some niche cases (e.g. you may use a release build with debug information to track a bug or profile a piece of code)