cleavir compilation policy

1.0.0

System for representing and interrogating compiler policies.

Lisp has OPTIMIZE declarations for expressing that some lexical block should be compiled with an emphasis on "speed", and stuff like that. That's nice, but in the compiler's view, vague. This system converts OPTIMIZE information into specific and actionable "policies" for the rest of the compiler.

Policies are separate objects computed from the optimize info. A policy consists of several "qualities", which are just a symbol naming it and a value. Qualities are computed from the generic function COMPUTE-POLICY-QUALITY, which is called from the overall COMPUTE-POLICY function.

What policies exist is defined by the POLICY-QUALITIES generic function. Cleavir defines several of its own policies with DEFINE-CLEAVIR-COMPILER-POLICY, but implementations can as well for their own compiler transforms. POLICY-QUALITIES's return value has the same format as CLEAVIR-ENV:OPTIMIZE-QUALITIES, and an APPEND method combo.

Every AST and instruction stores the policy that was computed for its lexical region. (This means that policies should be kept cached.) When a compiler transform wants to know whether it should do something to such an object, it checks the POLICY-VALUE for whatever it's doing.

For implementors:

  1. If you have your own policies, return something from POLICY-QUALITIES when specified on your global environment. If you don't have your own policies don't sweat it.
  2. Define a method for COMPUTE-POLICY-QUALITY specialized on each policy quality (including cleavir's) and your global environment. Example:
(defmethod cleavir-policy:compute-policy-quality
    ((name (eql 'cleavir-typed-transforms:insert-type-checks))
     optimize (env sys:global-environment))
  (= (cleavir-policy:optimize-value optimize 'safety) 3))
  1. Make sure your environments respect the optimize info protocols in cleavir/environment. You can use COMPUTE-POLICY to compute policies from optimize decls, but you should avoid doing this on every optimize-info call.

System Information

1.0.0
BSD
https://s-expressionists.github.io/Cleavir/cleavir-compilation-policy/
https://github.com/s-expressionists/Cleavir/issues
https://github.com/s-expressionists/Cleavir.git

Definition Index