llvm dev - Apr 2010 - [LLVMdev] Proposal for a new LLVM concurrency memory model

On 27 April 2010 16:46, David Greene <dag at cray.com>
wrote:
> It shouldn't be very hard for the compiler to detect the second case.
> It's a pretty straightforward pattern.  For everything else it would
> have to assume case #1.
The only problem is that threads are rarely within language specs, so
the compiler would have to choose one particular flavour of threads or
"find out" what flavour is being used. That would require the compiler
to know all / implement all types, which are not only time consuming
and error prone, but not the compiler's job in the first place.

cheers,
--renato

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On Tuesday 27 April 2010 11:01:16 Renato Golin wrote:
> On 27 April 2010 16:46, David Greene <dag at cray.com> wrote:
> > It shouldn't be very hard for the compiler to detect the second
case.
> > It's a pretty straightforward pattern.  For everything else it
would
> > have to assume case #1.
>
> The only problem is that threads are rarely within language specs, so
> the compiler would have to choose one particular flavour of threads or
> "find out" what flavour is being used. That would require the
compiler
> to know all / implement all types, which are not only time consuming
> and error prone, but not the compiler's job in the first place.
The compiler has to know the threading model.  There's no way around
that.  gcc has the -pthread switch, for example.

The compiler integrates into a comprehensive programming environment.
It has to know what the environment provides and uses.  That _is_ very much 
the compiler's responsibility.

That's why target-independent code is so hard to write.  :)

Again, my vote is to define vector atomics as respecting atomicity across
elements and make it the compiler's and user's job to know when it can
use
them.

                          -Dave

On 27 April 2010 17:28, David Greene <dag at cray.com>
wrote:
> The compiler integrates into a comprehensive programming environment.
> It has to know what the environment provides and uses.  That _is_ very much
> the compiler's responsibility.
I agree the compilers should know about threads, but enough to work
around the issues and not start creating threads the user didn't ask
for.

I'm not against enhancing the compiler to that point, I just think
that you're digging too deep and Balrog might show up unexpectedly.
Thread issues can be daunting by themselves, automatically creating
threaded code is a recipe to disaster, IMHO.

> Again, my vote is to define vector atomics as respecting atomicity across
> elements and make it the compiler's and user's job to know when it
can use
> them.
By means of #pragmas?


cheers,
--renato

http://systemcall.org/

Reclaim your digital rights, eliminate DRM, learn more at
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