Great question—let's break this down step by step, since Dart's AOT compilation for cross-platform targets is a clever system, and comparing it to Swift helps highlight its unique design choices.

When you build a Flutter app in release mode (or use dart2native for standalone Dart apps), here's how your code gets transformed into platform-specific machine code:

1. Frontend: Kernel IR Generation
   First, the Dart compiler processes your source code into Kernel IR—a platform-agnostic intermediate representation. This step handles heavy lifting like type checking, dead-code elimination (tree shaking), and resolving imports. The best part? This IR is identical across all target platforms (Android, iOS, desktop), so the core logic parsing and optimization work only happens once, no matter where you're deploying.

2. Backend: Target-Specific Machine Code Compilation
   Next, the compiler takes the Kernel IR and feeds it into a backend tailored to your target platform:

   • For Android: Uses a backend optimized for ARM/ARM64 architectures, leveraging the Android NDK's toolchain to produce machine code that integrates seamlessly with the Android OS.
   • For iOS: Compiles directly to ARM64 machine code (the only architecture supported for modern iOS apps), and works with Xcode's tools to package the code into an IPA, ensuring compatibility with Apple's app sandbox and security rules.
   • For desktop platforms (Windows, macOS, Linux): Targets x86_64 or ARM64 (for Apple Silicon) using platform-native compilers.

   A critical detail: Dart's AOT compiler includes a stripped-down runtime alongside the machine code. This runtime handles essential Dart features like generational garbage collection, async/await scheduling, and remaining type safety checks that couldn't be fully compiled away. Unlike a JIT runtime, this is statically linked into your app—so users don't need a separate Dart VM installed on their device.

Swift and Dart both compile to native machine code, but their underlying approaches have some critical distinctions:

• Intermediate Representation Pipeline

  • Dart uses Kernel IR first, then moves to target-specific compilation. This shared frontend means cross-platform apps only go through initial parsing/optimization once.
  • Swift converts source code directly to Swift IR, then to LLVM IR, before using LLVM's backend to generate machine code. Swift is deeply integrated with the LLVM ecosystem, so it leans heavily on LLVM's mature optimizations and platform support.

• Memory Management

  • Dart's AOT runtime includes its own garbage collector. You don't have to manually manage memory (no retain/release calls), and the compiler doesn't insert reference-counting instructions into the machine code.
  • Swift uses Automatic Reference Counting (ARC)—a compile-time system where the compiler inserts retain/release calls into the machine code. Swift's runtime handles edge cases (like weak references), but most memory management work happens during compilation.

• Cross-Platform Focus

  • Dart was built from the ground up for cross-platform development. The Kernel IR and shared frontend make it straightforward to target multiple platforms with the same codebase, with minimal platform-specific adjustments.
  • Swift was initially designed for Apple's ecosystem (iOS, macOS, watchOS, tvOS) and later expanded to Linux/Windows. While it supports cross-platform development, its tooling and runtime are more tightly coupled to Apple's platforms, and cross-projects often require more platform-specific configuration.

• Dynamic vs. Static Optimization

  • Dart AOT prioritizes static optimization: it tries to resolve as many dynamic calls (like dynamic type invocations) as possible at compile time to eliminate runtime overhead. Any remaining dynamic behavior is handled by the runtime.
  • Swift supports dynamic features (like method swizzling and dynamic dispatch), but encourages static optimization via keywords like final, static, and private. Swift's runtime is more involved in handling dynamic operations, which adds small overhead but enables more flexible runtime behavior.

内容的提问来源于stack exchange，提问作者Josh