From 97c557eb04ab94ff8aa837722b7750aa8e54dcf4 Mon Sep 17 00:00:00 2001
From: Benedikt Meurer <bmeurer@google.com>
Date: Mon, 4 Feb 2019 14:39:29 +0100
Subject: [PATCH] Make modifierFlagsCache mandatory for Node objects

The `modifierFlagsCache` property is among the top properties that cause
megamorphic stub cache misses when having `tsc` build itself. This is
because it's added sort of randomly to a whole lot of different objects,
at arbitrary points after their initialization.

This also means that `modifierFlagsCache` is often not present on the
instances, which means that when missing on the megamorphic stub cache,
Node/V8 has to compute `NonExistent` handlers for the relevant inline
caches.

It's a lot cheaper to just make sure that the property is always
existent on the instance, and ideally also at the same offset. This
change ensures exactly that.

Drive-by-fix: Also make sure that `transformFlags` (and `parent`)
is always at the same offset for `Node` objects.
---
 src/compiler/types.ts    | 2 +-
 src/services/services.ts | 9 +++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index ff5ce74d31d..030926d969a 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -609,7 +609,7 @@ namespace ts {
     export interface Node extends TextRange {
         kind: SyntaxKind;
         flags: NodeFlags;
-        /* @internal */ modifierFlagsCache?: ModifierFlags;
+        /* @internal */ modifierFlagsCache: ModifierFlags;
         /* @internal */ transformFlags: TransformFlags;       // Flags for transforms, possibly undefined
         decorators?: NodeArray<Decorator>;                    // Array of decorators (in document order)
         modifiers?: ModifiersArray;                           // Array of modifiers
diff --git a/src/services/services.ts b/src/services/services.ts
index 6a63497d7e6..7f8e2aa45d3 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -16,17 +16,19 @@ namespace ts {
         public pos: number;
         public end: number;
         public flags: NodeFlags;
+        public modifierFlagsCache: ModifierFlags;
+        public transformFlags: TransformFlags;
         public parent: Node;
         public symbol!: Symbol; // Actually optional, but it was too annoying to access `node.symbol!` everywhere since in many cases we know it must be defined
         public jsDoc?: JSDoc[];
         public original?: Node;
-        public transformFlags: TransformFlags;
         private _children: Node[] | undefined;
 
         constructor(kind: SyntaxKind, pos: number, end: number) {
             this.pos = pos;
             this.end = end;
             this.flags = NodeFlags.None;
+            this.modifierFlagsCache = ModifierFlags.None;
             this.transformFlags = undefined!; // TODO: GH#18217
             this.parent = undefined!;
             this.kind = kind;
@@ -200,16 +202,19 @@ namespace ts {
         public pos: number;
         public end: number;
         public flags: NodeFlags;
+        public modifierFlagsCache: ModifierFlags;
+        public transformFlags: TransformFlags;
         public parent: Node;
         public symbol!: Symbol;
         public jsDocComments?: JSDoc[];
-        public transformFlags!: TransformFlags;
 
         constructor(pos: number, end: number) {
             // Set properties in same order as NodeObject
             this.pos = pos;
             this.end = end;
             this.flags = NodeFlags.None;
+            this.modifierFlagsCache = ModifierFlags.None;
+            this.transformFlags = undefined!; // TODO: GH#18217
             this.parent = undefined!;
         }