OpenCL - why are there any pointers at all?

Article: Introduction to OpenCL
By: Richard Cownie (tich.delete@this.pobox.com), December 17, 2010 7:02 am
Room: Moderated Discussions
Rob Thorpe (rthorpe@robertthorpeconsulting.com) on 12/17/10 wrote:
---------------------------

>Yes, and so can I in my Lisp and Basic programs :). My point is though that pointers
>aren't very useful unless you can dynamically allocate memory. In Open CL you can't
>dynamically allocate, that's one thing David mentions in the article.

If you're trying to write code that makes the most efficient
use of machine resources, then pointers are still quite
useful even without dynamic allocation. Suppose you have
an array and you want to pass around some kind of reference
to an element. If you have pointer variables, then you
just pass the pointer to the element, taking a single
register. If you don't have pointers, then you have to
pass around the base address of the array and an index,
and possibly do an extra address calculation from time to
time when you access it. Sure, optimizing compilers can
do a reasonable job these days of eliminating or reducing
such calculations by strength-reduction. But using a
pointer variable makes life easier and will occasionally
result in faster code.

And C programmers have been writing
"while (*dst++ = *src++);"
for 35 years or so and you're just going to tick them
needlessly if you take that away for no good reason.

Also, I haven't looked at OpenCL in detail, but if it
has type-casts as well as pointer variables, then for all
intents and purposes it *does* have dynamic allocation -
just declare char BigBuf[BIGBUFSIZE] and then write your
own functions to malloc() and free() from that buffer.
Though probably in most cases you'd want a more complex
system that would allow you to allocate from the different
classes of OpenCL memory rather than treating it all the
same.
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TopicPosted ByDate
OpenCL article onlineDavid Kanter2010/12/09 02:44 AM
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      It is difficult to runtime optimize away the difference between a CPU and GPUMark Roulo2010/12/10 07:50 PM
        It is difficult to runtime optimize away the difference between a CPU and GPUhobold2010/12/11 03:35 AM
          It is difficult to runtime optimize away the difference between a CPU and GPUMark Roulo2010/12/12 01:20 PM
            It is difficult to runtime optimize away the difference between a CPU and GPUhobold2010/12/12 03:31 PM
              It is difficult to runtime optimize away the difference between a CPU and GPUanon2010/12/12 04:24 PM
                It is difficult to runtime optimize away the difference between a CPU and GPUhobold2010/12/13 03:44 AM
        Specially when the language provides almost no hardware abstraction (NT)EduardoS2010/12/11 10:53 AM
    Performance portabilityWainwright2010/12/11 03:44 PM
      Performance portabilityEduardoS2010/12/11 03:57 PM
        Performance portabilityWainwright2010/12/11 04:02 PM
          Performance portabilityEduardoS2010/12/11 08:20 PM
            Performance portabilityWainwright2010/12/12 02:22 AM
      Performance portabilityDavid Kanter2010/12/11 05:53 PM
        Performance portabilityEduardoS2010/12/11 08:23 PM
          Performance portabilityDavid Kanter2010/12/11 09:06 PM
            Performance portabilityWainwright2010/12/12 02:26 AM
            Performance portabilityEduardoS2010/12/12 09:04 AM
  OpenCL article onlineAlan Commike2010/12/14 01:01 PM
  OpenCL - why are there any pointers at all?Rob Thorpe2010/12/16 03:45 AM
    OpenCL - why are there any pointers at all?EduardoS2010/12/16 01:51 PM
      OpenCL - why are there any pointers at all?Rob Thorpe2010/12/17 03:19 AM
        OpenCL - why are there any pointers at all?Richard Cownie2010/12/17 07:02 AM
          OpenCL - why are there any pointers at all?Rob Thorpe2010/12/17 08:29 AM
            OpenCL - why are there any pointers at all?Richard Cownie2010/12/17 09:13 AM
              OpenCL - why are there any pointers at all?Rob Thorpe2010/12/17 10:03 AM
                OpenCL - why are there any pointers at all?Richard Cownie2010/12/17 10:53 AM
                  OpenCL - why are there any pointers at all?Rob Thorpe2010/12/17 11:19 AM
                    OpenCL - why are there any pointers at all?Richard Cownie2010/12/17 11:51 AM
                OpenCL - why are there any pointers at all?hobold2010/12/17 11:06 AM
          OpenCL - why are there any pointers at all?EduardoS2010/12/18 07:58 AM
            OpenCL - why are there any pointers at all?anon2010/12/18 10:27 AM
            OpenCL - why are there any pointers at all?BorisG2010/12/18 10:33 AM
              OpenCL - why are there any pointers at all?Richard Cownie2010/12/18 02:39 PM
  OpenCL article onlineEmil Briggs2010/12/19 06:40 AM
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