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2015 Jul 22
2
[LLVMdev] some superoptimizer results
....uiuc.edu
> Sent: Wednesday, July 22, 2015 2:35:51 PM
> Subject: Re: [LLVMdev] some superoptimizer results
>
>
>
> Are you taking into account critical path length? Because e.g. for:
>
>
>
> %0:i64 = var
> %1:i1 = slt 18446744073709551615:i64, %0
> %2:i64 = subnsw 0:i64, %0
> %3:i64 = select %1, %0, %2
> infer %3
> %4:i64 = ashr %0, 63:i64
> %5:i64 = add %0, %4
> %6:i64 = xor %5, %4
> result %6
>
>
> In the former case, the cmp and sub are independent, so can be
> executed in parallel, while in the latter case all 3 instructio...
2015 Jul 22
3
[LLVMdev] some superoptimizer results
...some superoptimizer results
> >
> >
> >
> > Are you taking into account critical path length? Because e.g. for:
> >
> >
> >
> > %0:i64 = var
> > %1:i1 = slt 18446744073709551615:i64, %0
> > %2:i64 = subnsw 0:i64, %0
> > %3:i64 = select %1, %0, %2
> > infer %3
> > %4:i64 = ashr %0, 63:i64
> > %5:i64 = add %0, %4
> > %6:i64 = xor %5, %4
> > result %6
> >
> >
> > In the former case, the cmp and sub are independent,...
2015 Jul 22
8
[LLVMdev] some superoptimizer results
We (the folks working on Souper) would appreciate any feedback on these
IR-level superoptimizer results:
http://blog.regehr.org/extra_files/souper-jul-15.html
My impression is that while there's clearly plenty of material in here
that doesn't want to get implemented in an opt pass, there are a number
of gems hiding in there that are worth implementing.
Blog post containing