A new verified compiler backend for CakeML

Written by OlivierNicole (Olivier Nicole)
Published: 2016-09-17 (last updated: 2016-09-19)

CakeML is a descendant of ML. It has formalized semantics in HOL4. Full paper: PDF

  • End-to-end verified compilation from CakeML to x86-64.

v1.0 drawbacks

  • Too low-level for FP optimizations, awkward for target-specific optimizations.
  • Only one target available.


  • New backend designed for verified optimizations
  • Configurable + multiple targets
  • Basic support for FFI
  • 12 ILs for optimization.


ClosLang is a new IL of v2.0. It allows for functional-style optimizations, like multi-argument functions and closure conversion.

CakeML backend

  • Values in terms of 32-/64-bit words
  • Configurable data representation

The new backend also introduces an abstract GC specification.

Next step:

  • Concretize stack representation
  • Flatten code, compile to assembly
  • Encode assembly to target ISA.

Compiler semantics preservation

Observational semantics preservation

If the semantics of a program is not an error, then it is preserved by compilation (up to the point where it stops with an out-of-memory error).

Proof sizes: 100 K lines of HOL4, 6 developers, 2 years. We have a fine-grained control over the role of each IL.

To achieve this, data abstraction has complex invariants.

Ongoing & future work

  • Charguéraud's characteristic formulæ (ICFP '10, '11)
  • New compiler optimizations
  • v2.0 compiler bootstrap
  • Generational garbage collection