A Prolog compiler and its extension for OR-parallelism
Mats Carlsson · 1990
This report describes algorithms for the compiler component of the Aurora Or-Parallel Prolog system. The compiler translates one Prolog clause at a time into a sequence of abstract instructions. The instruction set is based on the sequential Warren Abstract Machine (WAM) with extensions for full Prolog, shallow backtracking, memory management and garbage collection, and for the SRI model of or-parallel execution of Prolog. Most of the described algorithms apply to compilation of sequential Prolog programs. The extensions introduced to support or-parallelism are minor, and concern pruning operators (cut and commit) and compile-time allocation of binding array offsets for permanent variables (generalised environment trimming). Code generation proper is kept separate from register allocation, and uses heuristics for finding a compilation order which minimises the number of register-register copies. After such copies have been coalesced where possible, register allocation is performed in a...