missed numeric optimizations with type-check

[tromey]

Consider if json--decode-utf16-surrogates checked the input types:

(defun json--decode-utf-16-surrogates (high low)
  "Return the code point represented by the UTF-16 surrogates HIGH and LOW."
  (cl-check-type high integer)
  (cl-check-type low integer)
  (+ (lsh (- high #xD800) 10) (- low #xDC00) #x10000))

This should compile to some ordinary arithmetic. Instead the compiler emits calls to Fminus, Qlsh, etc.

[tromey]

The issue is there's no lower-level IR which can represent unboxed values.