[cfe-dev] Random clang testing results

Daniel Dunbar daniel at zuster.org
Sun Mar 15 07:42:47 CDT 2009

On Sun, Mar 15, 2009 at 4:20 AM, Sebastian Redl <
sebastian.redl at getdesigned.at> wrote:

> Daniel Dunbar wrote:
> > I tried building Blender with clang today for fun. Went without a
> > hitch, although I had to use gcc for two files from ffmpeg with nasty
> > inline asm. Blender has about 600k lines of C code internally, and
> > another 600k from external libraries (like FFTW, ffmpeg, qhull, ...).
> How do compile times compare?

I didn't look; I'm close enough to having the new driver working that it
isn't worth trying to compare timings with the Python driver.

> > Some results from comparing renders on the two binaries are here:
> > http://t1.minormatter.com/~ddunbar/blender/times.html<http://t1.minormatter.com/%7Eddunbar/blender/times.html>
> > <http://t1.minormatter.com/%7Eddunbar/blender/times.html>
> >
> > A lot of rendering artifacts, but it is remotely possible this is a
> > Blender bug not a clang one. Several files show obvious flaws, on the
> > other hand.

> These artifacts look like floating point inaccuracies to me.

The edge rendering ones, yes. The red cube verse gray cube is probably
something else though. :)

Could it be that Clang generates code that makes these worse?

Maybe, although aside from constant folding, IRgen doesn't do too much in
this area. If I was going to hunt these things I would probably do a build
with llvm-gcc first to get a feel for frontend verse backend issue. My guess
is that the edge artifacts will also show up with llvm-gcc.

 - Daniel
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