This only seems to speedup value functions (not struct/callback or other C functions.)

From the referenced file: https://source.chromium.org/chromium/chromium/src/+/main:v8/...

* Currently supported return types: * - void * - bool * - int32_t * - uint32_t * - float32_t * - float64_t * Currently supported argument types: * - pointer to an embedder type * - JavaScript array of primitive types * - bool * - int32_t * - uint32_t * - int64_t * - uint64_t * - float32_t * - float64_t