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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - Loop unrolling doesn't take into account whether it will decrease or increase performance"
href="https://bugs.freedesktop.org/show_bug.cgi?id=83658#c3">Comment # 3</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - Loop unrolling doesn't take into account whether it will decrease or increase performance"
href="https://bugs.freedesktop.org/show_bug.cgi?id=83658">bug 83658</a>
from <span class="vcard"><a class="email" href="mailto:lemody@gmail.com" title="Tapani Pälli <lemody@gmail.com>"> <span class="fn">Tapani Pälli</span></a>
</span></b>
<pre>(In reply to Eero Tamminen from <a href="show_bug.cgi?id=83658#c2">comment #2</a>)
<span class="quote">> (In reply to <a href="show_bug.cgi?id=83658#c1">comment #1</a>)
> > FWIW there exists code to detect expressions that are constant within a loop
> > (during loop analysis), I think this could be used as starting point for
> > such optimization.
>
> Loop invariant code handling could also be the root cause making e.g.
> SynMark2 PSPhong 3x slower than it should be:
> - code doesn't get unrolled with all the loop invariant code inside the loop
> - this resulting in cascade effect that causes also other problems. e.g.
> stuff which on Windows GL is handled with push & no sampler, changes to
> (unecessarily looped) pull and makes thing sampler bound with Mesa instead
> of it being PS ALU bound</span >
For me it looks like invariant code in loop is not the problem within PSPhong
example, I will try to make a handwritten loop with invariant code to
investigate this optimization opportunity more.</pre>
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