MLton 20210117

# DeadCode

DeadCode is an optimization pass for the CoreML IntermediateLanguage, invoked from CoreMLSimplify.

## Description

This pass eliminates declarations from the Basis Library not needed by the user program.

## Implementation

- dead-code.sig

- dead-code.fun

## Details and Notes

In order to compile small programs rapidly, a pass of dead code elimination is run in order to eliminate as much of the Basis Library as possible. The dead code elimination algorithm used is not safe in general, and only works because the Basis Library implementation has special properties:

- it terminates

- it performs no I/O

The dead code elimination includes the minimal set of declarations from the Basis Library so that there are no free variables in the user program (or remaining Basis Library implementation). It has a special hack to include all bindings of the form:

     val _ = ...

There is an ML Basis annotation, deadCode true, that governs which code is subject to this unsafe dead-code elimination.