[llvm] r193853 - LoopVectorizer: If dependency checks fail try runtime checks

[Hal Finkel]

----- Original Message -----
> 
> On Oct 31, 2013, at 10:36 PM, Hal Finkel <hfinkel at anl.gov> wrote:
> 
> > Arnold,
> > 
> > FWIW, this looks related to a question that I asked earlier today:
> > http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-October/067083.html
> > 
> 
> The array bounds check is only added when the dependency check fails.
> Once we extend SCEV for your example, in whatever way we decide to
> do that, we won’t emit these checks anymore.
> 
> > If a guard already exists (as in the example from my post), and the
> > vectorizer also adds one, does anything after the vectorizer clean
> > that up?
> > 
> 
> The runtime checks we add are different from the guard you added in
> your example. Not as clever. The loop vectorizer’s runtime checks
> just test no-overlapping'ness of the accesses in the loop. We don’t
> take dependency information into account for building those checks.

Do the runtime checks account for the store-to-load forwarding issue?

 -Hal

> 
> Best,
> Arnold

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory