Motivation and Context

Closes #1924 (closed)

This MR implements the algorithm from the paper "Compiling Pattern Matching to Good Decision Trees" for pattern matching compiler.

This algorithm performs better than the previous one in the cases when there are nested pattens in a match expression coupled with wildcards in between.

In some cases we can see more than 80% reduction in code size (compared to the old algorthim).

This algorithm simpler to implement and this also removes the pattern simplification pass (pattern_simpl.ml) which was needed by the old algorithm for compressing the matches. The new algorithm generates smaller automaton/match so there is not need for simplification/compression.

Description

Component

• compiler
• website
• webide
• vscode-plugin
• debugger

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement (non-breaking change that improves performance)
• None (change with no changelog)

Changelog

We implement a new algorithm for the pattern-matching compiler which reduces the size of generated code in some cases.

In some cases we observed upto 80% reduction in generated code.

Example

type t = A | B

type p = (t * t * t * t)

let main (p : p) (_ : int) : operation list * int = 
  [], (match p with
    A,A,A,A -> 1
  | B,B,B,B -> 1
  | _,A,A,A -> 2
  | _,B,B,B -> 2
  | _,_,A,A -> 3
  | _,_,B,B -> 3
  | _,_,_,A -> 4
  | _,_,_,B -> 4)

Before

$ ligo.67 info measure-contract x.mligo 
3920 bytes

After

$ ligo info measure-contract x.mligo 
468 bytes

Checklist:

• Changes follow the existing coding style (use dune @fmt to check).
• Tests for the changes have been added (for bug fixes / feature).
• Documentation has been updated.
• Changelog description has been added (if appropriate).
• Start titles under ## Changelog section with #### (if appropriate).
• There is no image or uploaded file in changelog
• Examples in changed behaviour have been added to the changelog (for breaking change / feature).