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

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

packages/compiler-cli/ngcc/src/sourcemaps/source_file.ts

@@ -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(
+      let outgoingStartIndex =
-          bSource.flattenedMappings,
+          findLastMappingIndexBefore(bSource.flattenedMappings, incomingStart, false, 0);
-          mapping => compareSegments(mapping.generatedSegment, incomingStart) <= 0);
       if (outgoingStartIndex < 0) {
         outgoingStartIndex = 0;
       }
       const outgoingEndIndex = incomingEnd !== undefined ?
-          findLastIndex(
+          findLastMappingIndexBefore(
-              bSource.flattenedMappings,
+              bSource.flattenedMappings, incomingEnd, true, outgoingStartIndex) :
-              mapping => compareSegments(mapping.generatedSegment, incomingEnd) < 0) :
           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])) {
+ * @param mappings The collection of mappings whose segment-markers we are searching.
-      return index;
+ * @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 matchingIndex;
 }
 
 /**

packages/compiler-cli/ngcc/test/sourcemaps/source_file_spec.ts

@@ -10,15 +10,14 @@ import {encode} from 'sourcemap-codec';
 import {absoluteFrom} from '../../../src/ngtsc/file_system';
 import {runInEachFileSystem} from '../../../src/ngtsc/file_system/testing';
 import {RawSourceMap} from '../../src/sourcemaps/raw_source_map';
-import {SourceFile, computeLineLengths, extractOriginalSegments, parseMappings} from '../../src/sourcemaps/source_file';
+import {SegmentMarker} from '../../src/sourcemaps/segment_marker';
+import {Mapping, SourceFile, computeLineLengths, extractOriginalSegments, findLastMappingIndexBefore, parseMappings} from '../../src/sourcemaps/source_file';
 
 runInEachFileSystem(() => {
   describe('SourceFile and utilities', () => {
     let _: typeof absoluteFrom;
 
-    beforeEach(() => {
+    beforeEach(() => { _ = absoluteFrom; });
-      _ = absoluteFrom;
-    });
 
     describe('parseMappings()', () => {
       it('should be an empty array for source files with no source map', () => {
@@ -84,6 +83,205 @@ runInEachFileSystem(() => {
          });
     });
 
+    describe('findLastMappingIndexBefore', () => {
+      it('should find the highest mapping index that has a segment marker below the given one if there is not an exact match',
+         () => {
+           const marker5: SegmentMarker = {line: 0, column: 50};
+           const marker4: SegmentMarker = {line: 0, column: 40};
+           const marker3: SegmentMarker = {line: 0, column: 30};
+           const marker2: SegmentMarker = {line: 0, column: 20};
+           const marker1: SegmentMarker = {line: 0, column: 10};
+           const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+               marker => ({ generatedSegment: marker } as Mapping));
+
+           const marker: SegmentMarker = {line: 0, column: 35};
+           const index = findLastMappingIndexBefore(mappings, marker, /* exclusive */ false, 0);
+           expect(index).toEqual(2);
+         });
+
+      it('should find the highest mapping index that has a segment marker (when there are duplicates) below the given one if there is not an exact match',
+         () => {
+           const marker5: SegmentMarker = {line: 0, column: 50};
+           const marker4: SegmentMarker = {line: 0, column: 30};
+           const marker3: SegmentMarker = {line: 0, column: 30};
+           const marker2: SegmentMarker = {line: 0, column: 20};
+           const marker1: SegmentMarker = {line: 0, column: 10};
+           const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+               marker => ({ generatedSegment: marker } as Mapping));
+
+           const marker: SegmentMarker = {line: 0, column: 35};
+           const index = findLastMappingIndexBefore(mappings, marker, /* exclusive */ false, 0);
+           expect(index).toEqual(3);
+         });
+
+      it('should find the last mapping if the segment marker is higher than all of them', () => {
+        const marker5: SegmentMarker = {line: 0, column: 50};
+        const marker4: SegmentMarker = {line: 0, column: 40};
+        const marker3: SegmentMarker = {line: 0, column: 30};
+        const marker2: SegmentMarker = {line: 0, column: 20};
+        const marker1: SegmentMarker = {line: 0, column: 10};
+        const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+            marker => ({ generatedSegment: marker } as Mapping));
+
+        const marker: SegmentMarker = {line: 0, column: 60};
+
+        const index = findLastMappingIndexBefore(mappings, marker, /* exclusive */ false, 0);
+        expect(index).toEqual(4);
+      });
+
+      it('should return -1 if the segment marker is lower than all of them', () => {
+        const marker5: SegmentMarker = {line: 0, column: 50};
+        const marker4: SegmentMarker = {line: 0, column: 40};
+        const marker3: SegmentMarker = {line: 0, column: 30};
+        const marker2: SegmentMarker = {line: 0, column: 20};
+        const marker1: SegmentMarker = {line: 0, column: 10};
+        const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+            marker => ({ generatedSegment: marker } as Mapping));
+
+        const marker: SegmentMarker = {line: 0, column: 5};
+
+        const index = findLastMappingIndexBefore(mappings, marker, /* exclusive */ false, 0);
+        expect(index).toEqual(-1);
+      });
+
+      describe('[exact match inclusive]', () => {
+        it('should find the matching segment marker mapping index if there is only one of them',
+           () => {
+             const marker5: SegmentMarker = {line: 0, column: 50};
+             const marker4: SegmentMarker = {line: 0, column: 40};
+             const marker3: SegmentMarker = {line: 0, column: 30};
+             const marker2: SegmentMarker = {line: 0, column: 20};
+             const marker1: SegmentMarker = {line: 0, column: 10};
+
+             const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+                 marker => ({ generatedSegment: marker } as Mapping));
+             const index = findLastMappingIndexBefore(mappings, marker3, /* exclusive */ false, 0);
+             expect(index).toEqual(2);
+           });
+
+        it('should find the highest matching segment marker mapping index if there is more than one of them',
+           () => {
+             const marker5: SegmentMarker = {line: 0, column: 50};
+             const marker4: SegmentMarker = {line: 0, column: 30};
+             const marker3: SegmentMarker = {line: 0, column: 30};
+             const marker2: SegmentMarker = {line: 0, column: 20};
+             const marker1: SegmentMarker = {line: 0, column: 10};
+
+             const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+                 marker => ({ generatedSegment: marker } as Mapping));
+             const index = findLastMappingIndexBefore(mappings, marker3, /* exclusive */ false, 0);
+             expect(index).toEqual(3);
+           });
+      });
+
+      describe('[exact match exclusive]', () => {
+        it('should find the preceding mapping index if there is a matching segment marker', () => {
+          const marker5: SegmentMarker = {line: 0, column: 50};
+          const marker4: SegmentMarker = {line: 0, column: 40};
+          const marker3: SegmentMarker = {line: 0, column: 30};
+          const marker2: SegmentMarker = {line: 0, column: 20};
+          const marker1: SegmentMarker = {line: 0, column: 10};
+
+          const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+              marker => ({ generatedSegment: marker } as Mapping));
+          const index = findLastMappingIndexBefore(mappings, marker3, /* exclusive */ true, 0);
+          expect(index).toEqual(1);
+        });
+
+        it('should find the highest preceding mapping index if there is more than one matching segment marker',
+           () => {
+             const marker5: SegmentMarker = {line: 0, column: 50};
+             const marker4: SegmentMarker = {line: 0, column: 30};
+             const marker3: SegmentMarker = {line: 0, column: 30};
+             const marker2: SegmentMarker = {line: 0, column: 20};
+             const marker1: SegmentMarker = {line: 0, column: 10};
+
+             const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+                 marker => ({ generatedSegment: marker } as Mapping));
+             const index = findLastMappingIndexBefore(mappings, marker3, /* exclusive */ false, 0);
+             expect(index).toEqual(3);
+           });
+      });
+
+      describe('[with lowerIndex hint', () => {
+        it('should find the highest mapping index above the lowerIndex hint that has a segment marker below the given one if there is not an exact match',
+           () => {
+             const marker5: SegmentMarker = {line: 0, column: 50};
+             const marker4: SegmentMarker = {line: 0, column: 40};
+             const marker3: SegmentMarker = {line: 0, column: 30};
+             const marker2: SegmentMarker = {line: 0, column: 20};
+             const marker1: SegmentMarker = {line: 0, column: 10};
+             const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+                 marker => ({ generatedSegment: marker } as Mapping));
+
+             const marker: SegmentMarker = {line: 0, column: 35};
+             const index = findLastMappingIndexBefore(mappings, marker, /* exclusive */ false, 1);
+             expect(index).toEqual(2);
+           });
+
+        it('should return the lowerIndex mapping index if there is a single exact match and we are not exclusive',
+           () => {
+             const marker5: SegmentMarker = {line: 0, column: 50};
+             const marker4: SegmentMarker = {line: 0, column: 40};
+             const marker3: SegmentMarker = {line: 0, column: 30};
+             const marker2: SegmentMarker = {line: 0, column: 20};
+             const marker1: SegmentMarker = {line: 0, column: 10};
+             const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+                 marker => ({ generatedSegment: marker } as Mapping));
+
+             const marker: SegmentMarker = {line: 0, column: 30};
+             const index = findLastMappingIndexBefore(mappings, marker, /* exclusive */ false, 2);
+             expect(index).toEqual(2);
+           });
+
+        it('should return the lowerIndex mapping index if there are multiple exact matches and we are not exclusive',
+           () => {
+             const marker5: SegmentMarker = {line: 0, column: 50};
+             const marker4: SegmentMarker = {line: 0, column: 30};
+             const marker3: SegmentMarker = {line: 0, column: 30};
+             const marker2: SegmentMarker = {line: 0, column: 20};
+             const marker1: SegmentMarker = {line: 0, column: 10};
+             const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+                 marker => ({ generatedSegment: marker } as Mapping));
+
+             const marker: SegmentMarker = {line: 0, column: 30};
+             const index = findLastMappingIndexBefore(mappings, marker, /* exclusive */ false, 3);
+             expect(index).toEqual(3);
+           });
+
+        it('should return -1 if the segment marker is lower than the lowerIndex hint', () => {
+          const marker5: SegmentMarker = {line: 0, column: 50};
+          const marker4: SegmentMarker = {line: 0, column: 40};
+          const marker3: SegmentMarker = {line: 0, column: 30};
+          const marker2: SegmentMarker = {line: 0, column: 20};
+          const marker1: SegmentMarker = {line: 0, column: 10};
+          const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+              marker => ({ generatedSegment: marker } as Mapping));
+
+          const marker: SegmentMarker = {line: 0, column: 25};
+
+          const index = findLastMappingIndexBefore(mappings, marker, /* exclusive */ false, 2);
+          expect(index).toEqual(-1);
+        });
+
+        it('should return -1 if the segment marker is equal to the lowerIndex hint and we are exclusive',
+           () => {
+             const marker5: SegmentMarker = {line: 0, column: 50};
+             const marker4: SegmentMarker = {line: 0, column: 40};
+             const marker3: SegmentMarker = {line: 0, column: 30};
+             const marker2: SegmentMarker = {line: 0, column: 20};
+             const marker1: SegmentMarker = {line: 0, column: 10};
+             const mappings: Mapping[] = [marker1, marker2, marker3, marker4, marker5].map(
+                 marker => ({ generatedSegment: marker } as Mapping));
+
+             const marker: SegmentMarker = {line: 0, column: 30};
+
+             const index = findLastMappingIndexBefore(mappings, marker, /* exclusive */ true, 2);
+             expect(index).toEqual(-1);
+           });
+      });
+    });
+
     describe('SourceFile', () => {
       describe('flattenedMappings', () => {
         it('should be an empty array for source files with no source map', () => {