HCoop / hcoop / debian / mlton.git / blame
| Commit | Line | Data |
|---|---|---|
| 7f918cf1 CE |
1 | PolyEqual |
| 2 | ========= | |
| 3 | ||
| 4 | <:PolyEqual:> is an optimization pass for the <:SSA:> | |
| 5 | <:IntermediateLanguage:>, invoked from <:SSASimplify:>. | |
| 6 | ||
| 7 | == Description == | |
| 8 | ||
| 9 | This pass implements polymorphic equality. | |
| 10 | ||
| 11 | == Implementation == | |
| 12 | ||
| 13 | * <!ViewGitFile(mlton,master,mlton/ssa/poly-equal.fun)> | |
| 14 | ||
| 15 | == Details and Notes == | |
| 16 | ||
| 17 | For each datatype, tycon, and vector type, it builds and equality | |
| 18 | function and translates calls to `MLton_equal` into calls to that | |
| 19 | function. | |
| 20 | ||
| 21 | Also generates calls to `Word_equal`. | |
| 22 | ||
| 23 | For tuples, it does the equality test inline; i.e., it does not create | |
| 24 | a separate equality function for each tuple type. | |
| 25 | ||
| 26 | All equality functions are created only if necessary, i.e., if | |
| 27 | equality is actually used at a type. | |
| 28 | ||
| 29 | Optimizations: | |
| 30 | ||
| 31 | * for datatypes that are enumerations, do not build a case dispatch, | |
| 32 | just use `MLton_eq`, as the backend will represent these as ints | |
| 33 | ||
| 34 | * deep equality always does an `MLton_eq` test first | |
| 35 | ||
| 36 | * If one argument to `=` is a constant and the type will get | |
| 37 | translated to an `IntOrPointer`, then just use `eq` instead of the | |
| 38 | full equality. This is important for implementing code like the | |
| 39 | following efficiently: | |
| 40 | + | |
| 41 | ---- | |
| 42 | if x = 0 ... (* where x is of type IntInf.int *) | |
| 43 | ---- | |
| 44 | ||
| 45 | * Also convert pointer equality on scalar types to type specific | |
| 46 | primitives. |