Uno Platform AOT Compilation: Complete Cross-Platform Native Performance Guide

This post presents a full-scope study of AOT (ahead-of-time) compilation support in Uno Platform, covering execution modes, platform toolchains, configuration steps, optimization strategies, and compatibility constraints for iOS, Android, WebAssembly, and desktop targets.

Key points

• Four runtime execution modes: Interpreter (default, ~30x slower than compiled WASM), Mixed (InterpreterAndAOT, ~50% smaller than full AOT, recommended for WASM production), Full AOT (mandatory on iOS), and Jiterpreter (.NET 9+, runtime JIT within the interpreter, up to 10x speedup when combined with Profiled AOT).
• Platform toolchain matrix: iOS uses Mono Full AOT (required by Apple's no-dynamic-code policy / W^X memory protection); Android uses Mono AOT with optional LLVM backend (-p:EnableLLVM=true, ~20-40% perf gain) and Profile-Guided AOT; WebAssembly uses Mono AOT via Emscripten; Skia Desktop and WinUI 3 use .NET Native AOT (ILC + RyuJIT).
• .NET 9 milestones: Jiterpreter, incremental AOT builds, WebCIL packaging, and automatic Emscripten toolchain management (no manual EMSDK install; ARM64 host support on Windows/macOS/Linux).
• Version highlights: Uno 4.7 introduced Native AOT for Skia+GTK; Uno 5.6 delivered up to 10x WASM AOT performance; Uno 6.0 replaced WPF with a Win32 backend, cutting Windows blank-app size by 74%, iOS by 21%, and improving AOT build times by 35%. iOS startup on iPhone 13 dropped from 1.5s to 0.49s with the unified Skia engine.

iOS

• Full AOT is forced by the platform; no PublishAot needed. Release config relies on RuntimeIdentifier=ios-arm64, PublishTrimmed, and UnoXamlTrimming (Uno 6.0+).
• Trimming modes: None, SdkOnly (default), Full (aggressive; mitigate with [DynamicDependency] and LinkerConfig.xml).
• Not available on iOS: System.Reflection.Emit, DynamicMethod, Assembly.Load(byte[]), Roslyn scripting; RegexOptions.Compiled is ignored. Use source generators, [JsonSerializable]-based System.Text.Json source-gen serialization, and cached delegates instead.
• GC tuning via MtouchEnableSGenConc, MtouchNurserySize, or MONO_GC_PARAMS environment variables.

Android

• AOT must be explicitly enabled: RunAOTCompilation=true, EnableLLVM=true, AndroidEnableMarshalMethods=true (.NET 8+, reduces JNI overhead 15-25%), PublishTrimmed=true, AndroidEnableProfiledAot=true.
• Startup Tracing workflow: add Mono.AotProfiler.Android, run dotnet build -t:BuildAndStartAotProfiling with profiling disabled AOT, exercise the app 30-60s, then FinishAotProfiling to produce custom.aprof; integrate via <AndroidAotProfile Include="Android/custom.aprof" />.
• Trade-off matrix (relative to interpreter baseline): PG-AOT ≈120-140% size, ~90% perf (production default); Full AOT + LLVM ≈180-220% size, 100% perf, 2-3x build time.
• Google Play requires AAB format (-p:AndroidPackageFormat=aab) and arm64-v8a; multi-ABI builds scale AOT time linearly. String resource trimming via AndroidLinkResources can cut 10-30% of resource size.

WebAssembly

• Production setup: <WasmShellMonoRuntimeExecutionMode>InterpreterAndAOT</WasmShellMonoRuntimeExecutionMode> — active only on dotnet publish / Release builds.
• Profile-Guided AOT: set WasmShellGenerateAOTProfile=true, run typical scenarios without debugger, press Alt+Shift+P to download the .aotprofile, then include it via WasmShellEnableAotProfile (auto-detected under Platforms/WebAssembly/ with Uno.Sdk).
• Jiterpreter (.NET 9+): <WasmShellEnableJiterpreter>true</WasmShellEnableJiterpreter>; tune via WasmShellRuntimeOptions (--jiterpreter-estimate-heat, --jiterpreter-stats-enable); inspect stats with INTERNAL.jiterpreter_dump_stats() in the browser console. Recommended: enable Mixed AOT and Jiterpreter together — they are complementary.

Desktop

• Skia desktop targets (GTK/Linux/macOS/Windows) support .NET Native AOT for single-file self-contained deployment (supported since Uno 4.7). WPF does not support Native AOT — migrate to WinUI 3 or GTK. WinUI 3 with the Skia+Win32 path is the recommended Windows configuration on Uno 6.0+.

General compatibility advice

Verify third-party NuGet packages for trim-friendliness (IsTrimmable metadata), reflection/dynamic-proxy usage, native ARM64/P/Invoke availability, and known AOT issues before adoption; validate with trimmer warnings and on-device testing.