+;;; Modular functions
+
+;;; (ldb (byte s 0) (foo x y ...)) =
+;;; (ldb (byte s 0) (foo (ldb (byte s 0) x) y ...))
+;;;
+;;; and similar for other arguments.
+
+;;; Try to recursively cut all uses of LVAR to WIDTH bits.
+;;;
+;;; For good functions, we just recursively cut arguments; their
+;;; "goodness" means that the result will not increase (in the
+;;; (unsigned-byte +infinity) sense). An ordinary modular function is
+;;; replaced with the version, cutting its result to WIDTH or more
+;;; bits. For most functions (e.g. for +) we cut all arguments; for
+;;; others (e.g. for ASH) we have "optimizers", cutting only necessary
+;;; arguments (maybe to a different width) and returning the name of a
+;;; modular version, if it exists, or NIL. If we have changed
+;;; anything, we need to flush old derived types, because they have
+;;; nothing in common with the new code.
+(defun cut-to-width (lvar width)
+ (declare (type lvar lvar) (type (integer 0) width))
+ (labels ((reoptimize-node (node name)
+ (setf (node-derived-type node)
+ (fun-type-returns
+ (info :function :type name)))
+ (setf (lvar-%derived-type (node-lvar node)) nil)
+ (setf (node-reoptimize node) t)
+ (setf (block-reoptimize (node-block node)) t)
+ (setf (component-reoptimize (node-component node)) t))
+ (cut-node (node &aux did-something)
+ (when (and (not (block-delete-p (node-block node)))
+ (combination-p node)
+ (eq (basic-combination-kind node) :known))
+ (let* ((fun-ref (lvar-use (combination-fun node)))
+ (fun-name (leaf-source-name (ref-leaf fun-ref)))
+ (modular-fun (find-modular-version fun-name width)))
+ (when (and modular-fun
+ (not (and (eq fun-name 'logand)
+ (csubtypep
+ (single-value-type (node-derived-type node))
+ (specifier-type `(unsigned-byte* ,width))))))
+ (binding* ((name (etypecase modular-fun
+ ((eql :good) fun-name)
+ (modular-fun-info
+ (modular-fun-info-name modular-fun))
+ (function
+ (funcall modular-fun node width)))
+ :exit-if-null))
+ (unless (eql modular-fun :good)
+ (setq did-something t)
+ (change-ref-leaf
+ fun-ref
+ (find-free-fun name "in a strange place"))
+ (setf (combination-kind node) :full))
+ (unless (functionp modular-fun)
+ (dolist (arg (basic-combination-args node))
+ (when (cut-lvar arg)
+ (setq did-something t))))
+ (when did-something
+ (reoptimize-node node name))
+ did-something)))))
+ (cut-lvar (lvar &aux did-something)
+ (do-uses (node lvar)
+ (when (cut-node node)
+ (setq did-something t)))
+ did-something))
+ (cut-lvar lvar)))
+
+(defoptimizer (logand optimizer) ((x y) node)
+ (let ((result-type (single-value-type (node-derived-type node))))
+ (when (numeric-type-p result-type)
+ (let ((low (numeric-type-low result-type))
+ (high (numeric-type-high result-type)))
+ (when (and (numberp low)
+ (numberp high)
+ (>= low 0))
+ (let ((width (integer-length high)))
+ (when (some (lambda (x) (<= width x))
+ *modular-funs-widths*)
+ ;; FIXME: This should be (CUT-TO-WIDTH NODE WIDTH).
+ (cut-to-width x width)
+ (cut-to-width y width)
+ nil ; After fixing above, replace with T.
+ )))))))
+\f