diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 422e31b8d06..5ab8251d5f5 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -794,6 +794,18 @@ namespace ts {
         return deduplicated;
     }
 
+    export function insertSorted<T>(array: SortedArray<T>, insert: T, compare: Comparer<T>): void {
+        if (array.length === 0) {
+            array.push(insert);
+            return;
+        }
+
+        const insertIndex = binarySearch(array, insert, identity, compare);
+        if (insertIndex < 0) {
+            array.splice(~insertIndex, 0, insert);
+        }
+    }
+
     export function sortAndDeduplicate<T>(array: ReadonlyArray<T>, comparer: Comparer<T>, equalityComparer?: EqualityComparer<T>) {
         return deduplicateSorted(sort(array, comparer), equalityComparer || comparer);
     }
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 3a3f41ef138..d95fe5ec09c 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -5009,6 +5009,10 @@ namespace ts {
         newLength: number;
     }
 
+    export interface SortedArray<T> extends Array<T> {
+        " __sortedArrayBrand": any;
+    }
+
     /* @internal */
     export interface DiagnosticCollection {
         // Adds a diagnostic to this diagnostic collection.
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 3c76bcf3119..6dfe85e9d97 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -2443,11 +2443,10 @@ namespace ts {
     }
 
     export function createDiagnosticCollection(): DiagnosticCollection {
-        let nonFileDiagnostics: Diagnostic[] = [];
-        const fileDiagnostics = createMap<Diagnostic[]>();
-
+        let nonFileDiagnostics = [] as SortedArray<Diagnostic>;
+        const filesWithDiagnostics = [] as SortedArray<string>;
+        const fileDiagnostics = createMap<SortedArray<Diagnostic>>();
         let hasReadNonFileDiagnostics = false;
-        let diagnosticsModified = false;
         let modificationCount = 0;
 
         return {
@@ -2467,66 +2466,45 @@ namespace ts {
         }
 
         function add(diagnostic: Diagnostic): void {
-            let diagnostics: Diagnostic[];
+            let diagnostics: SortedArray<Diagnostic>;
             if (diagnostic.file) {
                 diagnostics = fileDiagnostics.get(diagnostic.file.fileName);
                 if (!diagnostics) {
-                    diagnostics = [];
+                    diagnostics = [] as SortedArray<Diagnostic>;
                     fileDiagnostics.set(diagnostic.file.fileName, diagnostics);
+                    insertSorted(filesWithDiagnostics, diagnostic.file.fileName, compareStringsCaseSensitive);
                 }
             }
             else {
                 // If we've already read the non-file diagnostics, do not modify the existing array.
                 if (hasReadNonFileDiagnostics) {
                     hasReadNonFileDiagnostics = false;
-                    nonFileDiagnostics = nonFileDiagnostics.slice();
+                    nonFileDiagnostics = nonFileDiagnostics.slice() as SortedArray<Diagnostic>;
                 }
 
                 diagnostics = nonFileDiagnostics;
             }
 
-            diagnostics.push(diagnostic);
-            diagnosticsModified = true;
+            insertSorted(diagnostics, diagnostic, compareDiagnostics);
             modificationCount++;
         }
 
         function getGlobalDiagnostics(): Diagnostic[] {
-            sortAndDeduplicate();
             hasReadNonFileDiagnostics = true;
             return nonFileDiagnostics;
         }
 
         function getDiagnostics(fileName?: string): Diagnostic[] {
-            sortAndDeduplicate();
             if (fileName) {
                 return fileDiagnostics.get(fileName) || [];
             }
 
-            const allDiagnostics: Diagnostic[] = [];
-            function pushDiagnostic(d: Diagnostic) {
-                allDiagnostics.push(d);
+            const fileDiags = flatMap(filesWithDiagnostics, f => fileDiagnostics.get(f));
+            if (!nonFileDiagnostics.length) {
+                return fileDiags;
             }
-
-            forEach(nonFileDiagnostics, pushDiagnostic);
-
-            fileDiagnostics.forEach(diagnostics => {
-                forEach(diagnostics, pushDiagnostic);
-            });
-
-            return sortAndDeduplicateDiagnostics(allDiagnostics);
-        }
-
-        function sortAndDeduplicate() {
-            if (!diagnosticsModified) {
-                return;
-            }
-
-            diagnosticsModified = false;
-            nonFileDiagnostics = sortAndDeduplicateDiagnostics(nonFileDiagnostics);
-
-            fileDiagnostics.forEach((diagnostics, key) => {
-                fileDiagnostics.set(key, sortAndDeduplicateDiagnostics(diagnostics));
-            });
+            fileDiags.unshift(...nonFileDiagnostics);
+            return fileDiags;
         }
     }
 
diff --git a/src/harness/rwcRunner.ts b/src/harness/rwcRunner.ts
index ef7a371b0c4..3631186bb48 100644
--- a/src/harness/rwcRunner.ts
+++ b/src/harness/rwcRunner.ts
@@ -170,7 +170,8 @@ namespace RWC {
             });
 
 
-            it("has the expected emitted code", () => {
+            it("has the expected emitted code", function(this: Mocha.ITestCallbackContext) {
+                this.timeout(10000); // Allow long timeouts for RWC js verification
                 Harness.Baseline.runMultifileBaseline(baseName, "", () => {
                     return Harness.Compiler.iterateOutputs(compilerResult.files);
                 }, baselineOpts, [".js", ".jsx"]);
diff --git a/src/server/types.ts b/src/server/types.ts
index 93ffeeccff1..021bf4c28d7 100644
--- a/src/server/types.ts
+++ b/src/server/types.ts
@@ -22,10 +22,6 @@ declare namespace ts.server {
         require?(initialPath: string, moduleName: string): RequireResult;
     }
 
-    export interface SortedArray<T> extends Array<T> {
-        " __sortedArrayBrand": any;
-    }
-
     export interface SortedReadonlyArray<T> extends ReadonlyArray<T> {
         " __sortedArrayBrand": any;
     }
diff --git a/src/server/utilities.ts b/src/server/utilities.ts
index c44419f8cf3..a086d95f910 100644
--- a/src/server/utilities.ts
+++ b/src/server/utilities.ts
@@ -232,18 +232,6 @@ namespace ts.server {
         return base === "tsconfig.json" || base === "jsconfig.json" ? base : undefined;
     }
 
-    export function insertSorted<T>(array: SortedArray<T>, insert: T, compare: Comparer<T>): void {
-        if (array.length === 0) {
-            array.push(insert);
-            return;
-        }
-
-        const insertIndex = binarySearch(array, insert, identity, compare);
-        if (insertIndex < 0) {
-            array.splice(~insertIndex, 0, insert);
-        }
-    }
-
     export function removeSorted<T>(array: SortedArray<T>, remove: T, compare: Comparer<T>): void {
         if (!array || array.length === 0) {
             return;
diff --git a/tests/baselines/reference/api/tsserverlibrary.d.ts b/tests/baselines/reference/api/tsserverlibrary.d.ts
index 9d338a9fd10..9a311428cc1 100644
--- a/tests/baselines/reference/api/tsserverlibrary.d.ts
+++ b/tests/baselines/reference/api/tsserverlibrary.d.ts
@@ -2775,6 +2775,9 @@ declare namespace ts {
         span: TextSpan;
         newLength: number;
     }
+    interface SortedArray<T> extends Array<T> {
+        " __sortedArrayBrand": any;
+    }
     interface SyntaxList extends Node {
         _children: Node[];
     }
@@ -4854,9 +4857,6 @@ declare namespace ts.server {
         trace?(s: string): void;
         require?(initialPath: string, moduleName: string): RequireResult;
     }
-    interface SortedArray<T> extends Array<T> {
-        " __sortedArrayBrand": any;
-    }
     interface SortedReadonlyArray<T> extends ReadonlyArray<T> {
         " __sortedArrayBrand": any;
     }
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
index 3a1fa35146c..f68a53e706e 100644
--- a/tests/baselines/reference/api/typescript.d.ts
+++ b/tests/baselines/reference/api/typescript.d.ts
@@ -2775,6 +2775,9 @@ declare namespace ts {
         span: TextSpan;
         newLength: number;
     }
+    interface SortedArray<T> extends Array<T> {
+        " __sortedArrayBrand": any;
+    }
     interface SyntaxList extends Node {
         _children: Node[];
     }