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vlist performance improvements; allocate vhash data inline

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* module/ice-9/vlist.scm (make-block): If we are making a hash table,
  allocate it inline with the contents.  Otherwise don't even add a
  pointer to the block.
  (block-hash-table?): New internal accessor.
  (block-ref*): Remove.  Vhash entries are no longer wrapped.
  (block-ref):
  (block-hash-table-next-offset):
  (block-hash-table-set-next-offset!):
  (block-hash-table-ref):
  (block-hash-table-set!):
  (block-hash-table-add!): Adapt to take content vector explicitly, and
  to expect the hash table inline with the contents.  Some of these
  accessors are new.  Adapt callers.
  (assert-vlist): New helper.
  (vlist-cons): Update comment.
  (vhash?): Update scheme to allocate the hash table and chain links
  inline with the contents.
  (%vhash-fold*, %vhash-assoc): Rewrite to be more performant.
This commit is contained in:
Andy Wingo 2012-04-23 21:42:40 +02:00
parent 985702f713
commit 4bd53c1ba3
1 changed files with 157 additions and 140 deletions
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297
module/ice-9/vlist.scm
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@ -70,15 +70,15 @@
(make-fluid 2))
(define-inlinable (make-block base offset size hash-tab?)
;; Return a block (and block descriptor) of SIZE elements pointing to BASE
;; at OFFSET. If HASH-TAB? is true, a "hash table" is also added.
;; Note: We use `next-free' instead of `last-used' as suggested by Bagwell.
;; XXX: We could improve locality here by having a single vector but currently
;; the extra arithmetic outweighs the benefits (!).
(vector (make-vector size)
base offset size 0
(and hash-tab? (make-vector size #f))))
;; Return a block (and block descriptor) of SIZE elements pointing to
;; BASE at OFFSET. If HASH-TAB? is true, we also reserve space for a
;; "hash table". Note: We use `next-free' instead of `last-used' as
;; suggested by Bagwell.
(if hash-tab?
(vector (make-vector (* size 3) #f)
base offset size 0)
(vector (make-vector size)
base offset size 0)))
(define-syntax-rule (define-block-accessor name index)
(define-inlinable (name block)
@ -89,7 +89,9 @@
(define-block-accessor block-offset 2)
(define-block-accessor block-size 3)
(define-block-accessor block-next-free 4)
(define-block-accessor block-hash-table 5)
(define-inlinable (block-hash-table? block)
(< (block-size block) (vector-length (block-content block))))
(define-inlinable (set-block-next-free! block next-free)
(vector-set! block 4 next-free))
@ -103,20 +105,35 @@
(vector-set! (block-content block) offset value)
#t)))
(define-inlinable (block-ref block offset)
(vector-ref (block-content block) offset))
;; Return the item at slot OFFSET.
(define-inlinable (block-ref content offset)
(vector-ref content offset))
(define-inlinable (block-ref* block offset)
(let ((v (block-ref block offset)))
(if (block-hash-table block)
(car v) ;; hide the vhash link
v)))
;; Return the offset of the next item in the hash bucket, after the one
;; at OFFSET.
(define-inlinable (block-hash-table-next-offset content size offset)
(vector-ref content (+ size size offset)))
(define-inlinable (block-hash-table-ref block offset)
(vector-ref (block-hash-table block) offset))
;; Save the offset of the next item in the hash bucket, after the one
;; at OFFSET.
(define-inlinable (block-hash-table-set-next-offset! content size offset
next-offset)
(vector-set! content (+ size size offset) next-offset))
(define-inlinable (block-hash-table-set! block offset value)
(vector-set! (block-hash-table block) offset value))
;; Returns the index of the last entry stored in CONTENT with
;; SIZE-modulo hash value KHASH.
(define-inlinable (block-hash-table-ref content size khash)
(vector-ref content (+ size khash)))
(define-inlinable (block-hash-table-set! content size khash offset)
(vector-set! content (+ size khash) offset))
;; Add hash table information for the item recently added at OFFSET,
;; with SIZE-modulo hash KHASH.
(define-inlinable (block-hash-table-add! content size khash offset)
(block-hash-table-set-next-offset! content size offset
(block-hash-table-ref content size khash))
(block-hash-table-set! content size khash offset))
(define block-null
;; The null block.
@ -143,13 +160,10 @@
(lambda (vl port)
(cond ((vlist-null? vl)
(format port "#<vlist ()>"))
((block-hash-table (vlist-base vl))
((vhash? vl)
(format port "#<vhash ~x ~a pairs>"
(object-address vl)
(vhash-fold (lambda (k v r)
(+ 1 r))
0
vl)))
(vlist-length vl)))
(else
(format port "#<vlist ~a>"
(vlist->list vl))))))
@ -159,9 +173,19 @@
;; The empty vlist.
(make-vlist block-null 0))
;; Asserting that something is a vlist is actually a win if your next
;; step is to call record accessors, because that causes CSE to
;; eliminate the type checks in those accessors.
;;
(define-inlinable (assert-vlist val)
(unless (vlist? val)
(throw 'wrong-type-arg
#f
"Not a vlist: ~S"
(list val)
(list val))))
(define-inlinable (block-cons item vlist hash-tab?)
(unless (vlist? vlist)
(error "Expected a vlist:" vlist))
(let ((base (vlist-base vlist))
(offset (1+ (vlist-offset vlist))))
(cond
@ -186,21 +210,24 @@
(define (vlist-cons item vlist)
"Return a new vlist with @var{item} as its head and @var{vlist} as its
tail."
;; Note: Calling `vlist-cons' on a vhash will not do the right thing: it
;; doesn't box ITEM so that it can have the hidden "next" link used by
;; vhash items, and it passes `#f' as the HASH-TAB? argument to
;; `block-cons'. However, inserting all the checks here has an important
;; performance penalty, hence this choice.
;; Note: Although the result of `vlist-cons' on a vhash is a valid
;; vlist, it is not a valid vhash. The new item does not get a hash
;; table entry. If we allocate a new block, the new block will not
;; have a hash table. Perhaps we can do something more sensible here,
;; but this is a hot function, so there are performance impacts.
(assert-vlist vlist)
(block-cons item vlist #f))
(define (vlist-head vlist)
"Return the head of @var{vlist}."
(assert-vlist vlist)
(let ((base (vlist-base vlist))
(offset (vlist-offset vlist)))
(block-ref* base offset)))
(block-ref (block-content base) offset)))
(define (vlist-tail vlist)
"Return the tail of @var{vlist}."
(assert-vlist vlist)
(let ((base (vlist-base vlist))
(offset (vlist-offset vlist)))
(if (> offset 0)
@ -210,6 +237,7 @@ tail."
(define (vlist-null? vlist)
"Return true if @var{vlist} is empty."
(assert-vlist vlist)
(let ((base (vlist-base vlist)))
(and (not (block-base base))
(= 0 (block-size base)))))
@ -226,6 +254,7 @@ tail."
(define (vlist-fold proc init vlist)
"Fold over @var{vlist}, calling @var{proc} for each element."
;; FIXME: Handle multiple lists.
(assert-vlist vlist)
(let loop ((base (vlist-base vlist))
(offset (vlist-offset vlist))
(result init))
@ -235,19 +264,18 @@ tail."
(done? (< next 0)))
(loop (if done? (block-base base) base)
(if done? (block-offset base) next)
(proc (block-ref* base offset) result))))))
(proc (block-ref (block-content base) offset) result))))))
(define (vlist-fold-right proc init vlist)
"Fold over @var{vlist}, calling @var{proc} for each element, starting from
the last element."
(define len (vlist-length vlist))
(let loop ((index (1- len))
(assert-vlist vlist)
(let loop ((index (1- (vlist-length vlist)))
(result init))
(if (< index 0)
result
(loop (1- index)
(proc (vlist-ref vlist index) result)))))
(proc (vlist-ref vlist index) result)))))
(define (vlist-reverse vlist)
"Return a new @var{vlist} whose content are those of @var{vlist} in reverse
@ -267,11 +295,12 @@ order."
(define (vlist-ref vlist index)
"Return the element at index @var{index} in @var{vlist}."
(assert-vlist vlist)
(let loop ((index index)
(base (vlist-base vlist))
(offset (vlist-offset vlist)))
(if (<= index offset)
(block-ref* base (- offset index))
(block-ref (block-content base) (- offset index))
(loop (- index offset 1)
(block-base base)
(block-offset base)))))
@ -279,6 +308,7 @@ order."
(define (vlist-drop vlist count)
"Return a new vlist that does not contain the @var{count} first elements of
@var{vlist}."
(assert-vlist vlist)
(let loop ((count count)
(base (vlist-base vlist))
(offset (vlist-offset vlist)))
@ -319,6 +349,7 @@ satisfy @var{pred}."
(define (vlist-length vlist)
"Return the length of @var{vlist}."
(assert-vlist vlist)
(let loop ((base (vlist-base vlist))
(len (vlist-offset vlist)))
(if (eq? base block-null)
@ -371,98 +402,94 @@ details."
;; associated with K1 and K2, respectively. The resulting layout is a
;; follows:
;;
;; ,--------------------.
;; | ,-> (K1 . V1) ---. |
;; | | | |
;; | | (K2 . V2) <--' |
;; | | |
;; +-|------------------+
;; | | |
;; | | |
;; | `-- O <---------------H
;; | |
;; `--------------------'
;; ,--------------------.
;; 0| ,-> (K1 . V1) | Vlist array
;; 1| | |
;; 2| | (K2 . V2) |
;; 3| | |
;; size +-|------------------+
;; 0| | | Hash table
;; 1| | |
;; 2| +-- O <------------- H
;; 3| | |
;; size * 2 +-|------------------+
;; 0| `-> 2 | Chain links
;; 1| |
;; 2| #f |
;; 3| |
;; size * 3 `--------------------'
;;
;; The bottom part is the "hash table" part of the vhash, as returned by
;; `block-hash-table'; the other half is the data part. O is the offset of
;; the first value associated with a key that hashes to H in the data part.
;; The (K1 . V1) pair has a "hidden" link to the (K2 . V2) pair; hiding the
;; link is handled by `block-ref'.
;; This API potentially requires users to repeat which hash function and which
;; equality predicate to use. This can lead to unpredictable results if they
;; are used in consistenly, e.g., between `vhash-cons' and `vhash-assoc', which
;; is undesirable, as argued in http://savannah.gnu.org/bugs/?22159 . OTOH, two
;; arguments can be made in favor of this API:
;; The backing store for the vhash is partitioned into three areas: the
;; vlist part, the hash table part, and the chain links part. In this
;; example we have a hash H which, when indexed into the hash table
;; part, indicates that a value with this hash can be found at offset 0
;; in the vlist part. The corresponding index (in this case, 0) of the
;; chain links array holds the index of the next element in this block
;; with this hash value, or #f if we reached the end of the chain.
;;
;; This API potentially requires users to repeat which hash function and
;; which equality predicate to use. This can lead to unpredictable
;; results if they are used in consistenly, e.g., between `vhash-cons'
;; and `vhash-assoc', which is undesirable, as argued in
;; http://savannah.gnu.org/bugs/?22159 . OTOH, two arguments can be
;; made in favor of this API:
;;
;; - It's consistent with how alists are handled in SRFI-1.
;;
;; - In practice, users will probably consistenly use either the `q', the `v',
;; or the plain variant (`vlist-cons' and `vlist-assoc' without any optional
;; argument), i.e., they will rarely explicitly pass a hash function or
;; equality predicate.
;; - In practice, users will probably consistenly use either the `q',
;; the `v', or the plain variant (`vlist-cons' and `vlist-assoc'
;; without any optional argument), i.e., they will rarely explicitly
;; pass a hash function or equality predicate.
(define (vhash? obj)
"Return true if @var{obj} is a hash list."
(and (vlist? obj)
(let ((base (vlist-base obj)))
(and base
(vector? (block-hash-table base))))))
(block-hash-table? (vlist-base obj))))
(define* (vhash-cons key value vhash #:optional (hash hash))
"Return a new hash list based on @var{vhash} where @var{key} is associated
with @var{value}. Use @var{hash} to compute @var{key}'s hash."
(let* ((key+value (cons key value))
(entry (cons key+value #f))
(vlist (block-cons entry vhash #t))
(base (vlist-base vlist))
(khash (hash key (block-size base))))
(let ((o (block-hash-table-ref base khash)))
(if o (set-cdr! entry o)))
(block-hash-table-set! base khash
(vlist-offset vlist))
vlist))
(assert-vlist vhash)
;; We should also assert that it is a hash table. Need to check the
;; performance impacts of that. Also, vlist-null is a valid hash
;; table, which does not pass vhash?. A bug, perhaps.
(let* ((vhash (block-cons (cons key value) vhash #t))
(base (vlist-base vhash))
(offset (vlist-offset vhash))
(size (block-size base))
(khash (hash key size))
(content (block-content base)))
(block-hash-table-add! content size khash offset)
vhash))
(define vhash-consq (cut vhash-cons <> <> <> hashq))
(define vhash-consv (cut vhash-cons <> <> <> hashv))
(define-inlinable (%vhash-fold* proc init key vhash equal? hash)
;; Fold over all the values associated with KEY in VHASH.
(define khash
(let ((size (block-size (vlist-base vhash))))
(and (> size 0) (hash key size))))
(define (visit-block base max-offset result)
(let* ((size (block-size base))
(content (block-content base))
(khash (hash key size)))
(let loop ((offset (block-hash-table-ref content size khash))
(result result))
(if offset
(loop (block-hash-table-next-offset content size offset)
(if (and (<= offset max-offset)
(equal? key (car (block-ref content offset))))
(proc (cdr (block-ref content offset)) result)
result))
(let ((next-block (block-base base)))
(if (> (block-size next-block) 0)
(visit-block next-block (block-offset base) result)
result))))))
(let loop ((base (vlist-base vhash))
(khash khash)
(offset (and khash
(block-hash-table-ref (vlist-base vhash)
khash)))
(max-offset (vlist-offset vhash))
(result init))
(let ((answer (and offset (block-ref base offset))))
(cond ((and (pair? answer)
(<= offset max-offset)
(let ((answer-key (caar answer)))
(equal? key answer-key)))
(let ((result (proc (cdar answer) result))
(next-offset (cdr answer)))
(loop base khash next-offset max-offset result)))
((and (pair? answer) (cdr answer))
=>
(lambda (next-offset)
(loop base khash next-offset max-offset result)))
(else
(let ((next-base (block-base base)))
(if (and next-base (> (block-size next-base) 0))
(let* ((khash (hash key (block-size next-base)))
(offset (block-hash-table-ref next-base khash)))
(loop next-base khash offset (block-offset base)
result))
result)))))))
(assert-vlist vhash)
(if (> (block-size (vlist-base vhash)) 0)
(visit-block (vlist-base vhash)
(vlist-offset vhash)
init)
init))
(define* (vhash-fold* proc init key vhash
#:optional (equal? equal?) (hash hash))
@ -485,34 +512,24 @@ value of @var{result} for the first call to @var{proc}."
;; associated with KEY is found or when the end-of-list is reached. Inline to
;; make sure `vhash-assq' gets to use the `eq?' instruction instead of calling
;; the `eq?' subr.
(define khash
(let ((size (block-size (vlist-base vhash))))
(and (> size 0) (hash key size))))
(define (visit-block base max-offset)
(let* ((size (block-size base))
(content (block-content base))
(khash (hash key size)))
(let loop ((offset (block-hash-table-ref content size khash)))
(if offset
(if (and (<= offset max-offset)
(equal? key (car (block-ref content offset))))
(block-ref content offset)
(loop (block-hash-table-next-offset content size offset)))
(let ((next-block (block-base base)))
(and (> (block-size next-block) 0)
(visit-block next-block (block-offset base))))))))
(let loop ((base (vlist-base vhash))
(khash khash)
(offset (and khash
(block-hash-table-ref (vlist-base vhash)
khash)))
(max-offset (vlist-offset vhash)))
(let ((answer (and offset (block-ref base offset))))
(cond ((and (pair? answer)
(<= offset max-offset)
(let ((answer-key (caar answer)))
(equal? key answer-key)))
(car answer))
((and (pair? answer) (cdr answer))
=>
(lambda (next-offset)
(loop base khash next-offset max-offset)))
(else
(let ((next-base (block-base base)))
(and next-base
(> (block-size next-base) 0)
(let* ((khash (hash key (block-size next-base)))
(offset (block-hash-table-ref next-base khash)))
(loop next-base khash offset
(block-offset base))))))))))
(assert-vlist vhash)
(and (> (block-size (vlist-base vhash)) 0)
(visit-block (vlist-base vhash)
(vlist-offset vhash))))
(define* (vhash-assoc key vhash #:optional (equal? equal?) (hash hash))
"Return the first key/value pair from @var{vhash} whose key is equal to