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Cache the regularized form of union types #37749

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Merged
merged 3 commits into from
Apr 3, 2020
Merged

Cache the regularized form of union types #37749

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d702b0d
Cache the regularized form of union types
weswigham Apr 2, 2020
853381c
Inline function because why not
weswigham Apr 2, 2020
cbf1b04
Introduce two fastpasths into isRelatedTo
weswigham Apr 3, 2020
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23 changes: 21 additions & 2 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -13459,7 +13459,7 @@ namespace ts {

function getRegularTypeOfLiteralType(type: Type): Type {
return type.flags & TypeFlags.Literal ? (<LiteralType>type).regularType :
type.flags & TypeFlags.Union ? getUnionType(sameMap((<UnionType>type).types, getRegularTypeOfLiteralType)) :
type.flags & TypeFlags.Union ? ((<UnionType>type).regularType || ((<UnionType>type).regularType = getUnionType(sameMap((<UnionType>type).types, getRegularTypeOfLiteralType)) as UnionType)) :
type;
}

Expand Down Expand Up @@ -15457,6 +15457,16 @@ namespace ts {
return isIdenticalTo(source, target);
}


// We fastpath comparing a type parameter to exactly its constraint, as this is _super_ common,
// and otherwise, for type parameters in large unions, causes us to need to compare the union to itself,
// as we break down the _target_ union first, _then_ get the source constraint - so for every
// member of the target, we attempt to find a match in the source. This avoids that in cases where
// the target is exactly the constraint.
if (source.flags & TypeFlags.TypeParameter && getConstraintOfType(source) === target) {
return Ternary.True;
}

// Try to see if we're relating something like `Foo` -> `Bar | null | undefined`.
// If so, reporting the `null` and `undefined` in the type is hardly useful.
// First, see if we're even relating an object type to a union.
Expand Down Expand Up @@ -15787,7 +15797,16 @@ namespace ts {
function eachTypeRelatedToType(source: UnionOrIntersectionType, target: Type, reportErrors: boolean, intersectionState: IntersectionState): Ternary {
let result = Ternary.True;
const sourceTypes = source.types;
for (const sourceType of sourceTypes) {
for (let i = 0; i < sourceTypes.length; i++) {
const sourceType = sourceTypes[i];
if (target.flags & TypeFlags.Union && (target as UnionType).types.length === sourceTypes.length) {
// many unions are mappings of one another; in such cases, simply comparing members at the same index can shortcut the comparison
const related = isRelatedTo(sourceType, (target as UnionType).types[i], /*reportErrors*/ false, /*headMessage*/ undefined, intersectionState);
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Not sure I see why this would help. Union constituents are sorted by their type ids and those are pretty random even when one union is a mapping of the other. Am I missing something?

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@weswigham weswigham Apr 3, 2020 •
edited
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Type IDs are assigned as they are made, and unions are sorted; ergo, unions are ordered by the order the types within them were created in - for a union that results from a mapping on another union, that means the resulting union will share the input union's order. We exploit this here by checking those corresponding elements against one another to make this common case linear in comparison time (when the result is assignable), rather than quadratic.

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This change is responsible for most of the performance improvements from the last commit, not the other one. The other one allows us to skip one silly quadratic comparison of a union to itself, while this is allowing us to compare BigUnion to DiscriminateType<BigUnion, "name", T> in a linear way (DiscriminateType is a distributive conditional, so produces a union of types which are ultimately identical to BigUnion, as T is constrained to the values of "name").

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Right, in cases where the mapping creates new type IDs for each element I can see how this helps.

if (related) {
result &= related;
continue;
}
}
const related = isRelatedTo(sourceType, target, reportErrors, /*headMessage*/ undefined, intersectionState);
if (!related) {
return Ternary.False;
Expand Down
2 changes: 2 additions & 0 deletions src/compiler/types.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -4651,6 +4651,8 @@ namespace ts {
export interface UnionType extends UnionOrIntersectionType {
/* @internal */
resolvedReducedType: Type;
/* @internal */
regularType: UnionType;
}

export interface IntersectionType extends UnionOrIntersectionType {
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