[Android, 9.0.60] Enabling LLVM on Android crashes the app at start

[janne-hmp]

Description

I've been trying to see if I can improve the performance of my game GnollHack in MAUI. Since LLVM is enabled on iOS in Release configuration, I tried to enabling it also for Android by setting EnableLLVM true in the project file. However, this leads to a crash at start. Tested on .NET 9.0.4 / MAUI 9.0.60.

Steps to Reproduce

1. Clone the reproduction repository at https://github.com/hyvanmielenpelit/GnollHackMAUIEasyBuild
2. Open GnollHackM.csproj project file under win/win32/xpl/GnollHackM
3. In Visual Studio 2022, open GnollHackM's project properties by right-clicking the project and selecting Properties from the popup menu
4. Scroll down to Android > Options section and find LLVM subtitle there. Tick the box "Use LLVM optimizing compiler", which sets EnableLLVM in the project file to true
5. Change the configuration to Release
6. Delete bin and obj directories if they exist
7. Build GnollHackM according to instructions in the repository
8. Start the game on your Android device by selecting the device from the debug dropdown list and then clicking the Start without Debugging green arrow.
9. The game crashes at start
10. (If you do not set EnableLLVM to true, the game starts successfully. Delete bin and obj directories first, though.)

Link to public reproduction project repository

https://github.com/hyvanmielenpelit/GnollHackMAUIEasyBuild

Version with bug

9.0.60 SR6

Is this a regression from previous behavior?

Not sure, did not test other versions

Last version that worked well

Unknown/Other

Affected platforms

Android

Affected platform versions

Android 15

Did you find any workaround?

No, I cannot use LLVM on Android at the moment. Perhaps it does not work properly there yet, generally or with SkiaSharp or the like.

Relevant log output

[PureWeen]

Can you attach a logcat file with your crash?
https://learn.microsoft.com/en-us/xamarin/android/deploy-test/debugging/android-debug-log?tabs=windows

@jonathanpeppers @jonpryor

[janne-hmp]

Sure. Here you go. The appropriate crash is the last one.

logcat.zip

[janne-hmp]

I found out that setting <AndroidEnableProfiledAot>false</AndroidEnableProfiledAot> prevents the startup crash. However, with this setting optimizing the libraries for size takes c. 10 minutes (up from 3 minutes with EnableLLVM = true and up from 1 minute with EnableLLVM = false), and the optimization is conducted on each build and deployment (so minimum 2 times / 20 min per deployment), while with AndroidEnableProfiledAot = true, the whole process seemed to take about 3 min with EnableLLVM = true and 1 minute when EnableLLVM = false.

[janne-hmp]

@jonathanpeppers I have a few questions regarding this overall:

• Why does AndroidEnableProfiledAot = false make LLVM slow (c. 10 min to optimize the libraries)? (Or why is LLVM so fast when the setting is true, c. 3 min to optimize the libraries)
• Why are all the libraries, especially the ones in the .NET framework, always optimized every time? Cannot the optimized versions of framework libraries be stored somewhere in the obj directory, wherefrom they could be retrieved on every build (perhaps rebuild would optimize them again)?
• Why is library optimization rerun on every deployment in addition to build when AndroidEnableProfiledAot = false, causing things to slow down by a factor of 2? (But not when the setting is true, speeding up deployment massively.)
• Why are there 4 processes doing the optimization for Android x64 libraries but seemingly just one process optimizing Android ARM64 libraries, thus being 4 times slower? Could the number of processes / threads be increased to e.g. 8 processes / threads, making the best use of available processor capacity (now one process takes only 7% of CPU time)?

By (1) fixing the unnecessary library reoptimization before deployment, (2) optimizing the framework libraries only once, and (3) using 8 processes to optimize the remaining libraries, I think the build and deployment time in EnableLLVM = true and AndroidEnableProfiledAot = false could be brought down by a factor of at least 10.