On Fri, Jan 05, 2018 at 10:59:21AM +0000, Richard Earnshaw (lists) wrote:
> > But the condition could be just 'true' in the instruction encoding? That
> > is,
> > why do you do both the jump-around and the csel? Maybe I misunderstood
> > the RTL you appear to generate. I'd have expected an UNSPEC to avoid
> > the compiler messing up things.
> >
>
> That's why the intrinsic takes explicit bounds not a simple bool
> expressing the conditions. It prevents the optimizers from replacing
> the condition by value range propagation. That does restrict the
Preventing optimizers from replacing the condition can be done in many ways,
IFN, UNSPEC, ...
The question is if you really need it at the assembly level, or if you can
just do an unconditional branch or branch conditional on say comparison of
two constants, without any dynamic bounds.
Jakub
