CakeML/cakeml

Reduce GiveUps in data_to_word

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#186 opened on Nov 26, 2016

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Description

Some of the GiveUps in data_to_word could be compiler failures rather than generating code that aborts at runtime. This is better for the user since the failure is caught earlier. However, it requires making the compiler able to fail (CompileError) at data_to_word. For example, Cons tag becomes GiveUp if tag < dimword (:'a) DIV 16 which is decidable at compile time.

(An alternative hack, maybe, is to produce code that will produce an encoding error in asm (i.e., a jump that's too big). Probably too hard and hacky.)

Contributor guide

Research direction
Examine the data to word function in the CakeML compiler to identify GiveUp locations that can be decided at compile time. For each such GiveUp, determine how to produce a CompileError instead, requiring modification of the function's return type to allow failure. Focus on cases like Cons tag where the tag value is known at compile time and can be checked against the dimword constraint.
Tech stack
None
Domain
backendcompilers
Issue type
Refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Standard MLcompiler design
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
10