optimize away NIBBLES::%CHECK-BOUND when possible

(cl:in-package :nibbles)

(sb-c:deftransform %check-bound ((vector bound offset n-bytes)

				 ((simple-array (unsigned-byte 8) (*)) index

				  (and fixnum sb-vm:word)

				  (member 2 4 8 16))

				 * :node node)

  "optimize away bounds check"

  ;; cf. sb-c::%check-bound transform

  (cond ((sb-c:policy node (= sb-c::insert-array-bounds-checks 0))

	 'offset)

	((not (sb-c::constant-lvar-p bound))

	 (sb-c::give-up-ir1-transform))

	(t

	 (let* ((dim (sb-c::lvar-value bound))

		(n-bytes (sb-c::lvar-value n-bytes))

		(upper-bound `(integer 0 (,(- dim n-bytes -1)))))

	   (if (> n-bytes dim)

	       (sb-c::give-up-ir1-transform)

	       `(the ,upper-bound offset))))))

#.(flet ((specialized-includep (bitsize signedp setterp)

           (declare (ignorable bitsize signedp setterp))

           ;; Bleh.  No good way to solve this atm.