Performance improvements to this code...

Hi. We've done a fair bit of profiling to our system and have eliminated all
known major hotspots. We're now looking at other possibilities, and this
section of code might be a candidate:

(defmethod stream:stream-read-byte ((strm binary-input-stream))
  (declare (optimize speed))
  (with-slots ((buf buffer)
               (i index)
               (size bufsiz)) strm
    (declare (type fixnum i size)
             (type (array (unsigned-byte 8)) buf))
    (if (= i size)
        :eof
      (aref buf (the fixnum (1- (the fixnum (incf i))))))))

This code reflects the optimizations we've done that addressed a hotspot
identified by the profiler. I'm wondering if there's anything more to be
done here. In our test suite, this method is called more than any other in
the system (over 7million times), although it's found on the stack top just
2% of the time. I've looked at using svref instead of aref, but doing so
causes a runtime failure:

Error: In a call to SVREF: #(76 105 115 80 14 10 5 1 6 78 84 85 80 76 69 5 1
6 84 85 80 76 69 83 24 0 1 2 10 5 1 3 75 69 89 1 1 3 5 1 ...) is not of type
SIMPLE-VECTOR.
  1 (abort) Return to level 0.
  2 Return to top loop level 0.

Type :b for backtrace, :c <option number> to proceed,  or :? for other
options

DT 5 : 1 > 

The array is of type '(unsigned-byte 8)). Recommendations are appreciated.


David E. Young
Bloodhound Software, Inc.

For wisdom is more precious than rubies,
and nothing you desire can compare with her.
  -- Prov. 8:11

"But all the world understands my language."
  -- Franz Josef Haydn (1732 - 1809)


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Re: Performance improvements to this code...

>>>>> "DY" == David Young <Young> writes:

    DY> ... I've looked at using svref instead of aref, but doing so
    DY> causes a runtime failure:

That's because svref requires simple-vectors, and simple-vecors are 
not what we might think they are.  

http://clhs.lisp.se/Body/26_glo_s.htm#simple_vector

You have a specialized element type so your array cannot be a simple-vector.
KMP posted recently on the history of this confusing terminology:

http://groups.google.com/group/comp.lang.lisp/browse_frm/thread/48a6101ce0d70493/cd3f42887f4e4b6c

I don't see any obvious improvements other than perhaps declaring 
your array as a simple-array of one dimension containging (unsigned-byre 
8).  I don't know if this additional info helps the compiler though.

cheers,

BM

Re: Performance improvements to this code...

Young, David wrote:

>Hi. We've done a fair bit of profiling to our system and have eliminated all
>known major hotspots. We're now looking at other possibilities, and this
>section of code might be a candidate:
>
>(defmethod stream:stream-read-byte ((strm binary-input-stream))
>  (declare (optimize speed))
>  (with-slots ((buf buffer)
>               (i index)
>               (size bufsiz)) strm
>    (declare (type fixnum i size)
>             (type (array (unsigned-byte 8)) buf))
>    (if (= i size)
>        :eof
>      (aref buf (the fixnum (1- (the fixnum (incf i))))))))
>
>  
>

Try this, the disaasembly is much smaller,

(defmethod stream:stream-read-byte ((strm binary-input-stream))
  (declare (optimize (speed 3) (safety 0) (debug 0) (hcl:fixnum-safety 0)))

  (with-slots ((buf buffer)
               (i index)
               (size bufsiz)) strm
    (declare (type fixnum i size)
             (type (simple-array (unsigned-byte 8) (*)) buf))
    (if (= i size)
        :eof
      (aref buf (1- (incf i))))))