Excise the stupid fucking `set-*` opcodes
The book uses the horribly-confusingly-named `set-*` operations for handling
subterms in query mode. The author does this because he claims this is both
easier to understand and more performant. In reality it is neither of these
things.
If you just name the subterm-handling opcodes something not completely stupid,
like `handle-subterm-*` instead of `unify-*` it becomes obvious what they do.
Also, despite the fact that `put-*` instructions now need to set the WAM's
`mode`, we still get about a 10% speedup here, likely from some combination of
reducing the VM loop code size and simplifying the compilation process. So it's
not even more performant.
TL;DR: Just say "No" to `set-*`.
| author |
Steve Losh <steve@stevelosh.com> |
| date |
Sun, 10 Jul 2016 14:21:18 +0000 |
| parents |
792dfa2f9120 |
| children |
23d4dc2900a1 |
(in-package #:bones.wam)
(deftype cell ()
`(unsigned-byte ,+cell-width+))
(deftype cell-tag ()
`(unsigned-byte ,+cell-tag-width+))
(deftype cell-value ()
`(unsigned-byte ,+cell-value-width+))
(deftype store-index ()
`(integer 0 ,(1- +store-limit+)))
(deftype heap-index ()
`(integer ,+heap-start+ ,(1- +store-limit+)))
(deftype stack-index ()
`(integer ,+stack-start+ ,(1- +stack-end+)))
(deftype trail-index ()
`(integer 0 ,(1- +trail-limit+)))
(deftype register-index ()
`(integer 0 ,(1- +register-count+)))
(deftype functor-index ()
`(integer 0 ,(1- +functor-limit+)))
(deftype arity ()
`(integer 0 ,+maximum-arity+))
(deftype functor ()
'(cons symbol arity))
(deftype code-word ()
`(unsigned-byte ,+code-word-size+))
(deftype code-index ()
;; either an address or the sentinel
`(integer 0 ,(1- +code-limit+)))
(deftype opcode ()
`(integer 0 ,(1- +number-of-opcodes+)))
(deftype stack-frame-size ()
`(integer 4 ,+stack-frame-size-limit+))
(deftype stack-choice-size ()
;; TODO: is this actually right? check on frame size limit vs choice point
;; size limit...
`(integer 7 ,+stack-frame-size-limit+))
(deftype stack-frame-argcount ()
'arity)
(deftype continuation-pointer ()
'code-index)
(deftype environment-pointer ()
'stack-index)
(deftype backtrack-pointer ()
'stack-index)
(deftype stack-frame-word ()
'(or
environment-pointer ; CE
continuation-pointer ; CP
stack-frame-argcount ; N
cell)) ; Yn
(deftype stack-choice-word ()
'(or
environment-pointer ; CE
backtrack-pointer ; B
continuation-pointer ; CP, BP
stack-frame-argcount ; N
trail-index ; TR
heap-index ; H
cell)) ; An
(deftype stack-word ()
'(or stack-frame-word stack-choice-word))
;;;; Sanity Checks
;;; The values on the WAM stack are a bit of a messy situation. The WAM store
;;; is defined as an array of cells, but certain things on the stack aren't
;;; actually cells (e.g. the stored continuation pointer).
;;;
;;; This shouldn't be a problem (aside from being ugly) as long as our `cell`
;;; type is big enough to hold the values of these non-cell things. So let's
;;; just make sure that's the case...
(defun sanity-check-stack-type (type)
(assert (subtypep type 'cell) ()
"Type ~A is too large to fit into a cell!"
type)
(values))
(sanity-check-stack-type 'stack-frame-argcount)
(sanity-check-stack-type 'environment-pointer)
(sanity-check-stack-type 'continuation-pointer)
(sanity-check-stack-type 'backtrack-pointer)
(sanity-check-stack-type 'trail-index)
(sanity-check-stack-type 'stack-word)