perf(builtin): inline fast paths for slice access and pointer values

gs/builtin/builtin.ts

@@ -255,22 +255,29 @@ export function genericPointerRef<T>(
  * variable's address.
  */
 export function pointerValue<T>(value: T | VarRef<T> | null | undefined): T {
+  // A variable reference holds its value, and a struct that is not a boxed
+  // pointer is its own target. These property reads are much faster than
+  // the type and 'in' checks of pointerValueSlow, on the many kinds of
+  // objects seen here, and keep this function small enough to be inlined.
+  if (value !== null && value !== undefined) {
+    if ((value as any).__isVarRef === true) {
+      return (value as VarRef<T>).value
+    }
+    if ((value as any).__goValue === undefined) {
+      return value as T
+    }
+  }
+  return pointerValueSlow(value)
+}
+
+// pointerValueSlow is pointerValue for nil and boxed pointers.
+function pointerValueSlow<T>(value: T | VarRef<T> | null | undefined): T {
   if (value === null || value === undefined) {
     runtimePanic(
       'runtime error: invalid memory address or nil pointer dereference',
     )
   }
 
-  // A variable reference holds its value, and a struct that is not a boxed
-  // pointer is its own target. These property reads are much faster than
-  // the type and 'in' checks below, on the many kinds of objects seen here.
-  if ((value as any).__isVarRef === true) {
-    return (value as VarRef<T>).value
-  }
-  if ((value as any).__goValue === undefined) {
-    return value as T
-  }
-
   // A boxed pointer is unwrapped to its target.
   const boxed =
     typeof value === 'object' && value !== null && '__goValue' in value ?

gs/builtin/slice.ts

@@ -123,6 +123,22 @@ export function sliceRange(
 ): SliceRange<number>
 export function sliceRange<T>(
   slice: Slice<T> | TypedSlice | null | undefined,
+): SliceRange<T> | SliceRange<number> {
+  // A window object is its own window, and a plain array is a window over
+  // itself. They are handled here, in a function small enough for engines
+  // to inline, which also lets them avoid allocating the window of an array.
+  if (slice instanceof GoSlice) {
+    return slice
+  }
+  if (Array.isArray(slice) && (slice as any).__meta__ === undefined) {
+    return { backing: slice, offset: 0, length: slice.length }
+  }
+  return sliceRangeSlow(slice)
+}
+
+// sliceRangeSlow is sliceRange for nil, typed and proxied slices.
+function sliceRangeSlow<T>(
+  slice: Slice<T> | TypedSlice | null | undefined,
 ): SliceRange<T> | SliceRange<number> {
   // A nil slice has no elements.
   if (slice === null || slice === undefined) {
@@ -1325,25 +1341,29 @@ export function arrayToSlice<T>(
 export function sliceLen(
   slice: Slice<unknown> | unknown[] | TypedSlice | null | undefined,
 ): number {
-  // A nil slice has no elements.
-  if (slice === null || slice === undefined) {
-    return 0
-  }
-
-  // A window object and a plain array are the common cases, tested first
-  // without reading __meta__, which is slow on the many kinds of objects
-  // seen here. An array proxy (a window viewed as a Go array) has __meta__.
+  // A window object, a plain array and a typed slice are the common cases,
+  // tested here without reading __meta__, which is slow on the many kinds of
+  // objects seen here, in a function small enough for engines to inline. An
+  // array proxy (a window viewed as a Go array) has __meta__.
   if (slice instanceof GoSlice) {
     return slice.length
   }
+  if (ArrayBuffer.isView(slice)) {
+    return (slice as TypedSlice).length
+  }
   if (Array.isArray(slice) && (slice as any).__meta__ === undefined) {
     return slice.length
   }
+  return sliceLenSlow(slice)
+}
 
-  // A typed slice is a view of exactly its elements, whose window, if any,
-  // has the same length.
-  if (isTypedSlice(slice)) {
-    return slice.length
+// sliceLenSlow is sliceLen for nil slices, proxies and windowed arrays.
+function sliceLenSlow(
+  slice: Slice<unknown> | unknown[] | TypedSlice | null | undefined,
+): number {
+  // A nil slice has no elements.
+  if (slice === null || slice === undefined) {
+    return 0
   }
 
   // A slice proxy knows its length.
@@ -2332,6 +2352,36 @@ export function arrayIndex<
     | TypedSlice
     | null
     | undefined,
+>(collection: C, index: number): ArrayIndexValue<C> {
+  // An index in range of a window object, a typed slice or a plain array is
+  // read here, in a function small enough for engines to inline into hot
+  // loops; arrayIndexSlow handles the other representations and panics.
+  if (collection instanceof GoSlice) {
+    if (index >= 0 && index < collection.length) {
+      return collection.backing[collection.offset + index] as ArrayIndexValue<C>
+    }
+  } else if (ArrayBuffer.isView(collection)) {
+    if (index >= 0 && index < (collection as TypedSlice).length) {
+      return (collection as TypedSlice)[index] as ArrayIndexValue<C>
+    }
+  } else if (Array.isArray(collection) && (collection as any).__meta__ === undefined) {
+    if (index >= 0 && index < collection.length) {
+      return collection[index] as ArrayIndexValue<C>
+    }
+  }
+  return arrayIndexSlow(collection, index)
+}
+
+// arrayIndexSlow is arrayIndex for the representations and indexes that its
+// fast path does not handle.
+function arrayIndexSlow<
+  C extends
+    | Slice<unknown>
+    | SliceProxy<unknown>
+    | unknown[]
+    | TypedSlice
+    | null
+    | undefined,
 >(collection: C, index: number): ArrayIndexValue<C> {
   if (collection === null || collection === undefined) {
     outOfRangeIndex(index, 0)

gs/builtin/type.ts

@@ -1948,10 +1948,16 @@ function markClonedStructValue<T>(copy: T): T {
 // value unchanged. A marked struct with no clone method is returned unchanged
 // rather than panicking.
 export function copyElement<T>(value: T): T {
-  // A value that is not an object is copied by value.
+  // A value that is not an object is copied by value, here in a function
+  // small enough for engines to inline; copyObjectElement copies the others.
   if (typeof value !== 'object' || value === null) {
     return value
   }
+  return copyObjectElement(value)
+}
+
+// copyObjectElement is copyElement for a value that is an object.
+function copyObjectElement<T>(value: T & object): T {
 
   // A struct value of a class is copied as its class copies it.
   if ((value as any)[structValueMarker] === true) {