Compiler Architecture

Two Frontends

1. K1/FE 1.0 (Legacy): Located in compiler/frontend/ - uses PSI and BindingContext
2. K2/FIR (Current): Located in compiler/fir/ - Frontend IR, the new compiler frontend

FIR Compilation Phases

FIR processes code through sequential phases (see FirResolvePhase.kt).

Key invariant: In phase B following phase A, all FIR elements visible in B are resolved to phase A.

IR (Intermediate Representation)

Located in compiler/ir/. Backend IR is used by all targets for:

• Lowering (transforming code to target-friendly form)
• Optimization
• Serialization to klibs

Backend implementations:

• compiler/ir/backend.jvm/ - JVM backend
• compiler/ir/backend.js/ - JavaScript backend
• compiler/ir/backend.wasm/ - WebAssembly backend
• kotlin-native/backend.native/ - Native backend