[llvm-dev] Questions about jump threading optimization and what we can do

Karl Rehm via llvm-dev
Sun, 02 Feb 2020 17:45:38 -0000

Holy crap, I completely missed that. I'm sorry! That's my fault.

On Sun, Feb 2, 2020 at 12:15 PM Johannes Doerfert <jdoerfert at anl.gov>
wrote:

> On 01/30, Karl Rehm via llvm-dev wrote:
> > Since the bug report here: https://bugs.llvm.org/show_bug.cgi?id=44679
> I've
> > been thinking about cases like it, such as:
https://godbolt.org/z/Fwq8mn
> >
> > I wonder what we can do about this in a general sense. As far as I can
> > tell, the jump threading algorithm is *really* conservative, which is
one
> > reason this isn't working as well as I'd hope; however, we
don't want to
> > produce irreducible control flow that the other passes would work less
> > effectively on. Thoughts?
>
> I'm confused. In your godbold link you run it with O0 which disables
> almost all transformations. If we take the IR, remove the optnone
> attribute, run mem2reg and jump-threading we get what I think is
> reasonable:
>   https://godbolt.org/z/u3fcTZ
>
> Please correct me if I misunderstand anything here.
>
> Cheers,
>   Johannes
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20200202/34db416d/attachment.html>