perf(reflect): cache derived types and skip repeated checks

gs/reflect/type.ts

@@ -300,6 +300,10 @@ function convertValue(x: ReflectValue, ft: Type, t: Type): ReflectValue {
 }
 
 function internType(t: Type): Type {
+  // A canonical type interns to itself, so it needs no identity key.
+  if (internedTypes.has(t)) {
+    return t
+  }
   const key = typeIdentityKey(t)
   $.markReflectTypeIdentity(t, key)
   const existing = canonicalTypes.get(key)
@@ -309,9 +313,13 @@ function internType(t: Type): Type {
     return existing
   }
   canonicalTypes.set(key, t)
+  internedTypes.add(t)
   return t
 }
 
+// internedTypes holds the canonical types, which internType returned.
+const internedTypes = new WeakSet<Type>()
+
 function mergeTypeMetadata(target: Type, source: Type): void {
   if (target instanceof BasicType && source instanceof BasicType) {
     target.mergeMethodSignatures(source.methodSignatures())
@@ -805,14 +813,15 @@ export class Value {
   }
 
   public clone(): Value {
-    const cloned = new Value(
-      this._value,
-      this._type,
-      this._parentVarRef,
-      this._parentStruct,
-      this._fieldName,
-      this._interfaceValue,
-    )
+    // The fields of a constructed Value are already normalized, so the copy
+    // takes them as they are rather than checking them again.
+    const cloned = new Value()
+    cloned._value = this._value
+    cloned._type = this._type
+    cloned._parentVarRef = this._parentVarRef
+    cloned._parentStruct = this._parentStruct
+    cloned._fieldName = this._fieldName
+    cloned._interfaceValue = this._interfaceValue
     cloned._addressable = this._addressable
     return cloned
   }
@@ -5575,13 +5584,29 @@ export function ArrayOf(length: number, elem: Type): Type {
   return internType(new ArrayType(elem, length))
 }
 
+// sliceTypes and pointerTypes cache the slice and pointer type of each
+// type, which SliceOf and PointerTo would otherwise intern again on every
+// call, as reflect.New does.
+const sliceTypes = new WeakMap<Type, Type>()
+const pointerTypes = new WeakMap<Type, Type>()
+
 export function SliceOf(t: Type): Type {
-  return internType(new SliceType(t))
+  let st = sliceTypes.get(t)
+  if (st === undefined) {
+    st = internType(new SliceType(t))
+    sliceTypes.set(t, st)
+  }
+  return st
 }
 
 export function PointerTo(t: Type | null): Type | null {
   if (t === null) return null
-  return internType(new PointerType(t))
+  let pt = pointerTypes.get(t)
+  if (pt === undefined) {
+    pt = internType(new PointerType(t))
+    pointerTypes.set(t, pt)
+  }
+  return pt
 }
 
 export function PtrTo(t: Type | null): Type | null {

gs/reflect/value.ts

@@ -109,22 +109,32 @@ function newStructPointer(typ: Type): ReflectValue {
 // newStructValue returns a new zero struct of the type typ, which has no
 // registered constructor, such as an anonymous struct type.
 function newStructValue(typ: Type): ReflectValue {
-  type StructValueInstance = Record<string, ReflectValue>
+  const StructValue = structValueClass(typ)
+  return new StructValue() as ReflectValue
+}
 
-  // The fields are own properties of the struct object, starting at zero.
-  const initFields = (value: StructValueInstance): void => {
-    for (let i = 0; i < typ.NumField(); i++) {
-      const field = typ.Field(i)
-      const key = structFieldStorageKey(typ, i)
-      value[key] = zeroReflectValue(field.Type!)
-    }
+type StructValueInstance = Record<string, ReflectValue>
+
+// structValueClasses caches the class of the values of each struct type
+// without a registered constructor, so its values share one shape.
+const structValueClasses = new WeakMap<Type, new () => StructValueInstance>()
+
+// structValueClass returns the class of the values of the struct type typ.
+// Like a generated struct class, its constructor makes a zero value.
+function structValueClass(typ: Type): new () => StructValueInstance {
+  const cached = structValueClasses.get(typ)
+  if (cached !== undefined) {
+    return cached
   }
 
   // A clone copies each field.
   const StructValue = class {
+    constructor() {
+      initStructFields(typ, this as unknown as StructValueInstance)
+    }
+
     public clone(): unknown {
       const cloned = new StructValue() as unknown as StructValueInstance
-      initFields(cloned)
       for (const key of Object.keys(this)) {
         cloned[key] = (this as unknown as StructValueInstance)[key]
       }
@@ -135,10 +145,19 @@ function newStructValue(typ: Type): ReflectValue {
   Object.defineProperty(StructValue, '__typeInfo', {
     value: typeInfoFromReflectType(typ),
   })
+  const ctor = StructValue as unknown as new () => StructValueInstance
+  structValueClasses.set(typ, ctor)
+  return ctor
+}
 
-  const value = new StructValue() as unknown as StructValueInstance
-  initFields(value)
-  return value as ReflectValue
+// initStructFields sets the fields of the struct value of type typ to zero,
+// as own properties of the struct object.
+function initStructFields(typ: Type, value: StructValueInstance): void {
+  for (let i = 0; i < typ.NumField(); i++) {
+    const field = typ.Field(i)
+    const key = structFieldStorageKey(typ, i)
+    value[key] = zeroReflectValue(field.Type!)
+  }
 }
 
 // Copy copies the contents of src to dst until either dst has been filled