Investigate limitations and document findings of enabling NativeAOT for MAUI iOS application #80907

Description

Investigate potential issues and limitations of NativeAOT with .NET MAUI iOS applications:

1. .NET MAUI template app
2. .NET MAUI Podcast app

Goals

• Document discovered findings and limitations
• Based on the results propose the follow-up work
• Measure performance of NativeAOT targeting iOS platforms, and compare results against MonoAOT, the measurements should include: the application size: disk size (SOD) and bundle size (.ipa), build and startup time

Preview 6

Our main focus for the initial releases is the application size.
Apps were built and measured using: https://github.com/xamarin/xamarin-macios/tree/release/8.0.1xx-preview6 release

.NET MAUI template app

Building a .NET MAUI iOS sample application dotnet new maui gives the following results:

Mono-p6 in the table represents results obtained with Mono .NET8 preview6, while NAOT-p6 represents results obtained with NativeAOT .NET8 preview6

Identified issues that contribute to the size regression with NativeAOT are:

• Step1 - Exclude assemblies from NativeAOT app bundles macios#18532
• Step2 - NativeAOT: investigate if we want _AggressiveAttributeTrimming set for NativeAOT macios#18479
• Step3 - Respect IsDynamicCodeSupported in more places in Linq.Expressions #88539
• Step4 (TBD) - NativeAOT: Trimming and extensions compatibility - implementation macios#18584

Estimated savings

• Estimated savings in app sizes by applying optimizations for NativeAOT from Step1 to Step4

  .NET MAUI ios app	Mono-p6	NAOT-p6	Step1	Step2	Step3	Step4
  SOD (Mb)	40,24	50,13	41,93	40,5	27,58	TBD
  .ipa (Mb)	14,68	16,59	13,43	12,85	10,23	TBD

  NOTE: Results for StepN mean that all the previous steps Step1..N have been implemented

• Estimated difference (%) in app sizes compared to Mono-p6 by applying optimizations for NativeAOT from Step1 to Step4

  .NET MAUI ios app	Mono-p6	NAOT-p6	Step1	Step2	Step3	Step4
  diff SOD (%)	NaN	24,56%	4,20%	0,64%	-31,46%	TBD
  diff .ipa (%)	NaN	13,00%	-8,53%	-12,48%	-30,32%	TBD

  NOTE: Diffs in the table mean that if for example we implement Step1 and Step2, the .ipa size with NativeAOT will be 12,48% smaller compared to Mono

.NET MAUI Podcast app

• NativeAOT produces static library that makes ld crash #88032
  • Workaround: NativeAOT: Do not pass -dead_strip to the native linker macios#18552

Estimated savings

• Preliminary data (only estimated for Step3 improvements with NativeAOT):

  .NET MAUI ios app	Mono-p6	Step3	diff (%)
  SOD (Mb)	62,67	43,59	-30,45%
  .ipa (Mb)	24,37	17,43	-28,47%

Preview 7

Apps were built and measured using: https://github.com/xamarin/xamarin-macios/tree/release/8.0.1xx-preview7 release. The results show that NativeAOT generates ~30% smaller applications compared to Mono (as it has been estimated above).

.NET MAUI template app

.NET MAUI Podcast app

Other findings

• Fix Infinite recursion when generated code wrongly dispatches explicit interface calls
  • Consider method accessibility in interface resolution #81409
• Objective-C interop and GC API support:
  • [NativeAOT] Low level API support for Objective-C scenarios #77472
• Support static registrar with NativeAOT:
  • Make the static registrar work with NativeAOT macios#17324
• Dynamic registrar with NativeAOT - [NOT A PROBLEM]
  • We did not detect any need to support dynamic registrar with NativeAOT so far - especially because NativeAOT does not seem to be required for inner-dev loop experience. Nevertheless, bellow are listed findings when dynamic registrar is enabled for NativeAOT:
    • When building the application with dynamic registrar, the application crashes when ObjC runtime tries to register UIKit.UIGestureRecognizer+Callback`1 type while it is fetching its interface map against Foundation.INSObjectProtocol:

    default 12:06:26.833235+0200    HelloMauiiOS    *** Terminating app due to uncaught exception 'System.ArgumentException', reason: 'Interface not found. (System.ArgumentException)
    at Internal.Reflection.Execution.ExecutionEnvironmentImplementation.VerifyInterfaceIsImplemented(RuntimeTypeHandle, RuntimeTypeHandle) + 0x78
    at System.Reflection.Runtime.TypeInfos.RuntimeTypeInfo.GetInterfaceMap(Type) + 0xa8
    at Registrar.SharedDynamic.PrepareInterfaceMethodMapping(Type) + 0x114
    at Registrar.Registrar.RegisterTypeUnsafe(Type, List`1&) + 0x1fbc
    at Registrar.Registrar.RegisterType(Type, List`1&) + 0x44
    at Registrar.DynamicRegistrar.Register(Type) + 0x18
    at ObjCRuntime.Class.GetClassHandle(Type, Boolean, Boolean&) + 0x168
    at Foundation.NSObject.AllocIfNeeded() + 0x40
    at UIKit.UIPanGestureRecognizer..ctor(Action`1) + 0x40
    at Microsoft.Maui.Controls.Platform.Compatibility.ShellFlyoutRenderer.Microsoft.Maui.Controls.Platform.Compatibility.IShellFlyoutRenderer.AttachFlyout(IShellContext context, UIViewController content) + 0xf8
    

    • GetInterfaceMap does not seem to be supported with uninstantiated generic types in NativeAOT. Only the most mainstream cases seem to be supported which is being tracked here: Type.GetInterfaceMap doesn't work for all cases #89157