JIT backbone specification

Purpose

The JIT is a thin development-time execution engine for fast feedback. AOT is the primary production path. Both use the same frontend, CLIF lowering, and runtime ABI boundary.

Primary components

• cranelift_jit::JITModule
• cranelift_module::Module trait
• cranelift_frontend::FunctionBuilder

JIT flow (per module)

1. Build target ISA via cranelift_native::builder().
2. Create JITModule with a JITBuilder.
3. Declare function signatures and import runtime ABI symbols.
4. Lower HIR into CLIF and call define_function.
5. Call finalize_definitions().
6. Retrieve function pointers with get_finalized_function.

JIT scope and constraints

• The frontend emits CLIF once.
• The module abstraction is shared with AOT.
• JIT must not implement platform syscall policy or backend-specific execution behavior.
• JIT imports runtime builtins through the shared ABI manifest used by AOT.
• For AOT, replace JITModule with ObjectModule.

JIT responsibilities

• Fast host-platform compilation and execution for development feedback.
• Runtime ABI symbol binding through shared runtime surface.
• Reuse of lowering semantics identical to AOT.

JIT non-goals

• Production artifact packaging and linker orchestration.
• Platform ownership for syscall behavior.
• Runtime ABI shape ownership.

Safety model

• All finalized function pointers remain valid until free_memory().
• Do not hold or call pointers after memory is freed.

Debug strategy

• Allow optional CLIF emission to files for testing.
• Use cranelift_reader to parse CLIF for golden tests.
• Keep JIT validation focused on thin-backend behavior over shared lowering/runtime boundaries.