llvm dev - May 2012 - [LLVMdev] SIV tests in LoopDependence Analysis, Sanjoy's patch

Hi all,

Sorry for having been quiet for so long, I have my university exams
going on, and will be able to contribute only after the coming Friday.

Thanks!
-- 
Sanjoy Das
http://playingwithpointers.com

On Sat, Apr 21, 2012 at 6:08 AM, Sanjoy Das <sanjoy at
playingwithpointers.com>
wrote:
>
> Sorry for having been quiet for so long, I have my university exams
> going on, and will be able to contribute only after the coming Friday.
Gents,

While you've been fooling around with exams, I have been focused with
laser-like intensity, or something...
Here are new versions of 4 SIV tests:

   - the Strong SIV test:
   https://sites.google.com/site/parallelizationforllvm/strong-siv-test
   - the Weak-Zero SIV test:
   https://sites.google.com/site/parallelizationforllvm/weak-zero-siv-test
   - the Weak-Crossing SIV test:
   https://sites.google.com/site/parallelizationforllvm/weak-crossing-siv-test
   - the Exact SIV test:
   https://sites.google.com/site/parallelizationforllvm/weak-siv-test

and our first MIV test:

   - the RDIV test:
   https://sites.google.com/site/parallelizationforllvm/rdiv-test

If you have any thoughts about this code, I'd be very interested in hearing
them.

I'm going to take a break from working on these low-level tests and spend
some time working top-down on the high-level structure of the Delta Test
(finding coupled subscripts, etc).

Preston
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On Mon, 14 May 2012 11:46:02 -0700
Preston Briggs <preston.briggs at gmail.com> wrote:
> On Sat, Apr 21, 2012 at 6:08 AM, Sanjoy Das
> <sanjoy at playingwithpointers.com> wrote:
> >
> > Sorry for having been quiet for so long, I have my university exams
> > going on, and will be able to contribute only after the coming
> > Friday.
> 
> Gents,
> 
> While you've been fooling around with exams, I have been focused with
> laser-like intensity, or something...
> Here are new versions of 4 SIV tests:
> 
>    - the Strong SIV test:
>    https://sites.google.com/site/parallelizationforllvm/strong-siv-test
>    - the Weak-Zero SIV test:
>    https://sites.google.com/site/parallelizationforllvm/weak-zero-siv-test
>    - the Weak-Crossing SIV test:
>   
https://sites.google.com/site/parallelizationforllvm/weak-crossing-siv-test
>    - the Exact SIV test:
>    https://sites.google.com/site/parallelizationforllvm/weak-siv-test
> 
> and our first MIV test:
> 
>    - the RDIV test:
>    https://sites.google.com/site/parallelizationforllvm/rdiv-test
Can you explain this comment:
> With minor algebra, this test can also be used for things like [c1 +
> a1*i + a2*j][c2].
> 
> If you have any thoughts about this code, I'd be very interested in
> hearing them.
I this look good, but, as you say below, we also need to work on the
top-level infrastructure. It will be hard to validate and evaluate
this code without a framework in which to use it.

One thing that I would like to mention is that 'use' here should also
include user feedback. This means being able to pass information back
to the frontends about which loops are being effectively analyzed, and
for loops that are not, why not.

 -Hal
> 
> I'm going to take a break from working on these low-level tests and
> spend some time working top-down on the high-level structure of the
> Delta Test (finding coupled subscripts, etc).
> 
> Preston


-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory

Preston Briggs wrote:
> On Sat, Apr 21, 2012 at 6:08 AM, Sanjoy Das
> <sanjoy at playingwithpointers.com <mailto:sanjoy at
playingwithpointers.com>>
> wrote:
>  >
>  > Sorry for having been quiet for so long, I have my university exams
>  > going on, and will be able to contribute only after the coming
Friday.
>
> Gents,
>
> While you've been fooling around with exams, I have been focused with
> laser-like intensity, or something...
> Here are new versions of 4 SIV tests:
>
>   * the Strong SIV test:
>     https://sites.google.com/site/parallelizationforllvm/strong-siv-test
>   * the Weak-Zero SIV test:
>     https://sites.google.com/site/parallelizationforllvm/weak-zero-siv-test
>   * the Weak-Crossing SIV test:
>    
https://sites.google.com/site/parallelizationforllvm/weak-crossing-siv-test
>   * the Exact SIV test:
>     https://sites.google.com/site/parallelizationforllvm/weak-siv-test
>
> and our first MIV test:
>
>   * the RDIV test:
>     https://sites.google.com/site/parallelizationforllvm/rdiv-test
>
> If you have any thoughts about this code, I'd be very interested in
> hearing them.
One issue: don't use floating-point in LLVM. We want LLVM to behave the 
same on different computers, and practically that means avoiding floats. 
This code:

     double TMUL = BM.sdiv(G).roundToDouble(true);
     if (TMUL > 0) {
       TL = fmax(TL, (-X).roundToDouble(true) / TMUL);

from the RDIV test is not okay. You can use APFloat if you like, that's 
our soft-coded float library that produces reproducible results.

Nick
> I'm going to take a break from working on these low-level tests and
> spend some time working top-down on the high-level structure of the
> Delta Test (finding coupled subscripts, etc).
>
> Preston
>
>
>
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