diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 4b64f1299f..3dc2735d00 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -1061,10 +1061,10 @@ namespace ts {
     /**
      * Stable sort of an array. Elements equal to each other maintain their relative position in the array.
      */
-    export function stableSort<T>(array: ReadonlyArray<T>, comparer: Comparer<T>) {
+    export function stableSort<T>(array: ReadonlyArray<T>, comparer: Comparer<T>): SortedReadonlyArray<T> {
         const indices = array.map((_, i) => i);
         stableSortIndices(array, indices, comparer);
-        return indices.map(i => array[i]);
+        return indices.map(i => array[i]) as SortedArray<T> as SortedReadonlyArray<T>;
     }
 
     export function rangeEquals<T>(array1: ReadonlyArray<T>, array2: ReadonlyArray<T>, pos: number, end: number) {
@@ -1156,7 +1156,7 @@ namespace ts {
      * @param offset An offset into `array` at which to start the search.
      */
     export function binarySearch<T, U>(array: ReadonlyArray<T>, value: T, keySelector: (v: T) => U, keyComparer: Comparer<U>, offset?: number): number {
-        return some(array) ? binarySearchKey(array, keySelector(value), keySelector, keyComparer, offset) : -1;
+        return binarySearchKey(array, keySelector(value), keySelector, keyComparer, offset);
     }
 
     /**
@@ -2167,74 +2167,4 @@ namespace ts {
     export function fill<T>(length: number, cb: (index: number) => T): T[] {
         return new Array(length).fill(0).map((_, i) => cb(i));
     }
-
-    /**
-     * A list of sorted and unique values. Optimized for best performance when items are added
-     * in the sort order.
-     */
-    export class SortedUniqueList<T> implements Push<T> {
-        private relationalComparer: (a: T, b: T) => Comparison;
-        private equalityComparer: (a: T, b: T) => boolean;
-        private sortedAndUnique = true;
-        private copyOnWrite = false;
-        private unsafeArray: T[] = [];
-        private unsafeLast: T | undefined = undefined;
-
-        constructor(relationalComparer: Comparer<T>, equalityComparer: EqualityComparer<T>) {
-            this.relationalComparer = relationalComparer;
-            this.equalityComparer = equalityComparer;
-        }
-
-        get size() {
-            return this.unsafeArray.length;
-        }
-
-        get last() {
-            this.ensureSortedAndUnique();
-            return this.unsafeLast === undefined
-                ? this.unsafeLast = lastOrUndefined(this.unsafeArray)
-                : this.unsafeLast;
-        }
-
-        push(...values: T[]) {
-            for (const value of values) {
-                if (this.sortedAndUnique) {
-                    const last = this.last;
-                    if (last === undefined || this.relationalComparer(value, last) > 0) {
-                        this.unsafeAdd(value, /*sortedAndUnique*/ true);
-                        continue;
-                    }
-                    if (this.equalityComparer(value, last)) {
-                        continue;
-                    }
-                }
-                this.unsafeAdd(value, /*sortedAndUnique*/ false);
-            }
-        }
-
-        toArray(): ReadonlyArray<T> {
-            this.ensureSortedAndUnique();
-            this.copyOnWrite = true;
-            return this.unsafeArray;
-        }
-
-        private unsafeAdd(value: T, sortedAndUnique: boolean) {
-            if (this.copyOnWrite || this.unsafeArray === emptyArray) {
-                this.unsafeArray = this.unsafeArray.slice();
-                this.copyOnWrite = false;
-            }
-
-            this.unsafeArray.push(value);
-            this.unsafeLast = sortedAndUnique ? value : undefined;
-            this.sortedAndUnique = sortedAndUnique;
-        }
-
-        private ensureSortedAndUnique() {
-            if (!this.sortedAndUnique) {
-                this.unsafeArray = deduplicateSorted(stableSort(this.unsafeArray, this.relationalComparer) as any as SortedReadonlyArray<T>, this.equalityComparer) as any as T[];
-                this.unsafeLast = undefined;
-                this.sortedAndUnique = true;
-            }
-        }
-    }
 }
diff --git a/src/compiler/sourcemap.ts b/src/compiler/sourcemap.ts
index 700c6a9100..76cf24e51d 100644
--- a/src/compiler/sourcemap.ts
+++ b/src/compiler/sourcemap.ts
@@ -566,18 +566,18 @@ namespace ts {
             && value.sourcePosition !== undefined;
     }
 
-    function sameMappedPosition<T extends MappedPosition>(left: T, right: T) {
+    function sameMappedPosition(left: MappedPosition, right: MappedPosition) {
         return left.generatedPosition === right.generatedPosition
             && left.sourceIndex === right.sourceIndex
             && left.sourcePosition === right.sourcePosition;
     }
 
     function compareSourcePositions(left: SourceMappedPosition, right: SourceMappedPosition) {
-        return left.sourcePosition - right.sourcePosition;
+        return compareValues(left.sourceIndex, right.sourceIndex);
     }
 
     function compareGeneratedPositions(left: MappedPosition, right: MappedPosition) {
-        return left.generatedPosition - right.generatedPosition;
+        return compareValues(left.generatedPosition, right.generatedPosition);
     }
 
     function getSourcePositionOfMapping(value: SourceMappedPosition) {
@@ -598,8 +598,8 @@ namespace ts {
         const sourceFileCanonicalPaths = sourceFileAbsolutePaths.map(source => host.getCanonicalFileName(source) as Path);
         const sourceToSourceIndexMap = createMapFromEntries(sourceFileCanonicalPaths.map((source, i) => [source, i] as [string, number]));
         let decodedMappings: ReadonlyArray<MappedPosition> | undefined;
-        let generatedMappings: ReadonlyArray<MappedPosition> | undefined;
-        let sourceMappings: ReadonlyArray<ReadonlyArray<SourceMappedPosition>> | undefined;
+        let generatedMappings: SortedReadonlyArray<MappedPosition> | undefined;
+        let sourceMappings: ReadonlyArray<SortedReadonlyArray<SourceMappedPosition>> | undefined;
 
         return {
             getSourcePosition,
@@ -648,25 +648,25 @@ namespace ts {
 
         function getSourceMappings(sourceIndex: number) {
             if (sourceMappings === undefined) {
-                const lists: SortedUniqueList<SourceMappedPosition>[] = [];
+                const lists: SourceMappedPosition[][] = [];
                 for (const mapping of getDecodedMappings()) {
                     if (!isSourceMappedPosition(mapping)) continue;
                     let list = lists[mapping.sourceIndex];
-                    if (!list) lists[mapping.sourceIndex] = list = new SortedUniqueList(compareSourcePositions, sameMappedPosition);
+                    if (!list) lists[mapping.sourceIndex] = list = [];
                     list.push(mapping);
                 }
-                sourceMappings = lists.map(list => list.toArray());
+                sourceMappings = lists.map(list => sortAndDeduplicate<SourceMappedPosition>(list, compareSourcePositions, sameMappedPosition));
             }
             return sourceMappings[sourceIndex];
         }
 
         function getGeneratedMappings() {
             if (generatedMappings === undefined) {
-                const list = new SortedUniqueList(compareGeneratedPositions, sameMappedPosition);
+                const list: MappedPosition[] = [];
                 for (const mapping of getDecodedMappings()) {
                     list.push(mapping);
                 }
-                generatedMappings = list.toArray();
+                generatedMappings = sortAndDeduplicate(list, compareGeneratedPositions, sameMappedPosition);
             }
             return generatedMappings;
         }