[PATCH] D72906: [X86] Improve X86 cmpps/cmppd/cmpss/cmpsd intrinsics with strictfp

Thu Jan 23 22:12:25 PST 2020

craig.topper added a comment.

In D72906#1826849 <https://reviews.llvm.org/D72906#1826849>, @uweigand wrote:

> In D72906#1826122 <https://reviews.llvm.org/D72906#1826122>, @craig.topper wrote:
>
> > In D72906#1826061 <https://reviews.llvm.org/D72906#1826061>, @uweigand wrote:
> >
> > > > The constrained fcmp intrinsics don't allow the TRUE/FALSE predicates.
> > >
> > > Hmm, maybe they should then?   The only reason I didn't add them initially was that I wasn't sure they were useful for anything; if they are, it should be straightforward to add them back.
> >
> >
> > What would we lower it to on a target that doesn’t support it natively?
>
>
> Any supported compare (quiet or signaling as appropriate, just so we get the correct exceptions), and then ignore the result (and use true/false constant result instead)?

Sure. Is that something we want to force all targets to have to implement just to handle this case for X86? Unless we can come up with a generic DAG combine to pick a valid condition alternate so that the lowering code for each target doesn't have to deal with it.

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https://reviews.llvm.org/D72906