[LLVMdev] Help adding the Bullet physics sdk benchmark to the LLVM test suite?

Erwin Coumans erwin.coumans at gmail.com
Mon Jan 4 18:11:43 PST 2010

Hi Anton, and happy new year all,

>>One questions though: is it possible to "verify" the results of all
>>the computations somehow?

Good point, and there is no automated way currently, but we can work on
Note that simulation suffers from the 'butterfly effect', so the smallest
change anywhere,
(cpu, compiler etc) diverges into totally different results after a while.

There are a few ways of verification I can think of:

1) verifying by adding unit tests for all stages in the physics pipeline
(broadphase acceleration structures, closest point computation, constraint
Given known input and output we can check if the solution is within a
certain tolerance.

2) using the benchmark simulation and verifying the results frame by frame
and check for unusual behaviour

3) modify the benchmark so that it is easier to test the end result, even
through it might be different.
For example, we can drop a number of boxes above a bowl, and after a while
make sure all boxes are 'in' the bowl in a resting pose.

What are your thoughts?

2009/12/19 Anton Korobeynikov <anton at korobeynikov.info>

> Hello, Erwin
> > If you are interested, I think it is best to start with Bullet 2.75.
> > If it turns out that LLVM requires some modifications (due to current C++
> > limitations),
> > we can modify Bullet and go for an uncoming release such as Bullet 2.76
> > (planned around January 2010).
> I added bullet to LLVM testsuite. Basically I had to flatten source
> directories since this is a current requirement of the llvm testsuite
> harness.
> Some include paths tweaks were required due to this. Also, I disabled
> the time reports, since otherwise we cannot compare the outputs.
> bullet appeared to be ~20% slower for me compared to gcc 4.2.4, so,
> definitely something should be worked on :)
> One questions though: is it possible to "verify" the results of all
> the computations somehow? We need to care not only about speed, but
> about correctness too :)
> --
> With best regards, Anton Korobeynikov
> Faculty of Mathematics and Mechanics, Saint Petersburg State University
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