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perf(ngcc): use binary search when flattening mappings (#36027)

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The `@angular/core` package has a large number of source files
and mappings which exposed performance issues in the new source-map
flattening algorithm.

This change uses a binary search (rather than linear) when finding
matching mappings to merge. Initial measurements indicate that this
reduces processing time for `@angular/core` by about 50%.

PR Close #36027
This commit is contained in:
Pete Bacon Darwin
2020-03-09 17:03:36 +00:00
committed by Andrew Kushnir
parent c852ec9283
commit 348ff0c8ea
2 changed files with 236 additions and 15 deletions
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45
packages/compiler-cli/ngcc/src/sourcemaps/source_file.ts
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@ -147,16 +147,14 @@ export class SourceFile {
// The range with `incomingStart` at 2 and `incomingEnd` at 5 has outgoing start mapping of
// [1,0] and outgoing end mapping of [4, 6], which also includes [4, 3].
//
let outgoingStartIndex = findLastIndex(
bSource.flattenedMappings,
mapping => compareSegments(mapping.generatedSegment, incomingStart) <= 0);
let outgoingStartIndex =
findLastMappingIndexBefore(bSource.flattenedMappings, incomingStart, false, 0);
if (outgoingStartIndex < 0) {
outgoingStartIndex = 0;
}
const outgoingEndIndex = incomingEnd !== undefined ?
findLastIndex(
bSource.flattenedMappings,
mapping => compareSegments(mapping.generatedSegment, incomingEnd) < 0) :
findLastMappingIndexBefore(
bSource.flattenedMappings, incomingEnd, true, outgoingStartIndex) :
bSource.flattenedMappings.length - 1;
for (let bToCmappingIndex = outgoingStartIndex; bToCmappingIndex <= outgoingEndIndex;
@ -169,13 +167,38 @@ export class SourceFile {
}
}
function findLastIndex<T>(items: T[], predicate: (item: T) => boolean): number {
for (let index = items.length - 1; index >= 0; index--) {
if (predicate(items[index])) {
return index;
/**
*
* @param mappings The collection of mappings whose segment-markers we are searching.
* @param marker The segment-marker to match against those of the given `mappings`.
* @param exclusive If exclusive then we must find a mapping with a segment-marker that is
* exclusively earlier than the given `marker`.
* If not exclusive then we can return the highest mappings with an equivalent segment-marker to the
* given `marker`.
* @param lowerIndex If provided, this is used as a hint that the marker we are searching for has an
* index that is no lower than this.
*/
export function findLastMappingIndexBefore(
mappings: Mapping[], marker: SegmentMarker, exclusive: boolean, lowerIndex: number): number {
let upperIndex = mappings.length - 1;
const test = exclusive ? -1 : 0;
if (compareSegments(mappings[lowerIndex].generatedSegment, marker) > test) {
// Exit early since the marker is outside the allowed range of mappings.
return -1;
}
let matchingIndex = -1;
while (lowerIndex <= upperIndex) {
const index = (upperIndex + lowerIndex) >> 1;
if (compareSegments(mappings[index].generatedSegment, marker) <= test) {
matchingIndex = index;
lowerIndex = index + 1;
} else {
upperIndex = index - 1;
}
}
return -1;
return matchingIndex;
}
/**