MLton

PolyEqual is an optimization pass for the SSA IntermediateLanguage, invoked from SSASimplify.

Description

This pass implements polymorphic equality.

Implementation

Details and Notes

For each datatype, tycon, and vector type, it builds and equality function and translates calls to MLton_equal into calls to that function.

Also generates calls to Word_equal.

For tuples, it does the equality test inline; i.e., it does not create a separate equality function for each tuple type.

All equality functions are created only if necessary, i.e., if equality is actually used at a type.

Optimizations:

  • for datatypes that are enumerations, do not build a case dispatch, just use MLton_eq, as the backend will represent these as ints

  • deep equality always does an MLton_eq test first

  • If one argument to = is a constant and the type will get translated to an IntOrPointer, then just use eq instead of the full equality. This is important for implementing code like the following efficiently:

    if x = 0  ...    (* where x is of type IntInf.int *)

  • Also convert pointer equality on scalar types to type specific primitives.