[mono][perf] iOS disk size regression on 11 Nov 2022

[kotlarmilos]

Description

Microbenchmark improvement #78182 introduced concrete instances in addition to the gshared methods in AOT mode to optimize #78163.

For Mono iOS sample app, binary disk size (SOD) has increased by 8%.

Filename	SOD without concrete instances (80208e6)	SOD with concrete instances (486682a)
HelloiOS	17382408 bytes	18872480 bytes

Number of symbols has increased by 5k.

Filename	Number of symbols without concrete instances (80208e6)	Number of symbols with concrete instances (486682a)
HelloiOS	80007	85179

---

At the same time 80208e6 excluded dynamic libraries from the bundle as static linking is used.

For Mono iOS sample app, SOD has decreased by 5%.

File	Value (bytes)
HelloiOS	17042528
Info.plist	980
PkgInfo	8
Program.aotdata	4792
Program.deps.json	11754
Program.dll	6656
Program.runtimeconfig.json	1064
System.Console.aotdata	41952
System.Console.dll	17408
System.Private.CoreLib.aotdata	826296
System.Private.CoreLib.dll	998912
icudt.dat	1824544
icudt_CJK.dat	956416
icudt_EFIGS.dat	550320
icudt_no_CJK.dat	1071600
(EXCLUDED) libSystem.IO.Compression.Native.dylib	877152
(EXCLUDED) libSystem.Native.dylib	145728
(EXCLUDED) libSystem.Net.Security.Native.dylib	72064
(EXCLUDED) libSystem.Security.Cryptography.Native.Apple.dylib	104384

cc @ivanpovazan

Configuration

OS: iOS
Architecture: arm64
.NET version: 7.0.100-rc.1.22431.12

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[ivanpovazan]

@kotlarmilos if this affected Mono iOS sample size it probably regressed MAUI iOS sizes as well.
Do you know if this is being tracked already?

[kotlarmilos]

Good point, #78182 is not backported to .net7 so the regression is not present in MAUI iOS size measurements. I haven't found an issue related to the regression in MAUI iOS.

[ivanpovazan]

/cc @jonathanpeppers

[vargaz]

So the extra methods look to be Vector/Scalar method instances, these were previously shared, but now we generate specialized instances for them, leading to the size increase.

[vargaz]

Most of these methods appear to be the fallback methods in case SIMD is not found. If SIMD is enabled on ios, then this code will not be called, if it's not enabled, then the app should not call it since the performance is not good. So there should be a way to avoid generating code for them.