ISLE is a DSL that allows one to write instruction-lowering rules for a compiler backend. It is based on a "term-rewriting" paradigm in which the input -- some sort of compiler IR -- is, conceptually, a tree of terms, and we have a set of rewrite rules that turn this into another tree of terms.

This repository contains a prototype meta-compiler that compiles ISLE rules down to an instruction selector implementation in generated Rust code. The generated code operates efficiently in a single pass over the input, and merges all rules into a decision tree, sharing work where possible, while respecting user-configurable priorities on each rule.

The ISLE language is designed so that the rules can both be compiled into an efficient compiler backend and can be used in formal reasoning about the compiler. The compiler in this repository implements the former. The latter use-case is future work and outside the scope of this prototype, but at a high level, the rules can be seen as simple equivalences between values in two languages, and so should be translatable to formal constraints or other logical specification languages.

Some more details are in BA RFC #15; additional documentation will eventually be added to carefully specify the language semantics.

Sketch of Instruction Selector

Please see this Cranelift branch for an ongoing sketch of an instruction selector backend in Cranelift that uses ISLE.

Example Usage

    $ cargo build --release
    $ target/release/isle -i isle_examples/test.isle -o isle_examples/test.rs
    $ rustc isle_examples/test_main.rs