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Re: Reverting r278411
On Wed, Nov 20, 2019 at 03:46:29PM +0000, Richard Sandiford wrote:
> Segher Boessenkool <segher@kernel.crashing.org> writes:
> > UNLT & ORDERED is always LT. When would it not be true?
>
> LT traps on quiet NaNs for -ftrapping-math, UNLT and ORDERED don't.
No? -ftrapping-math makes nothing trap. The only thing it does is to
not do optimisations that are not valid if traps are considered to be
a user-visible thing.
Almost nothing ever traps on quiet NaNs.
And indeed the existing code is wrong for this already, as I mentioned
before (in the context of IEEE SNaNs). But yeah, we can do almost no
optimisation if trapping math is true, so we should skip everything in
that case. I wonder how much of existing GCC code breaks this as well
though, hrm.
Segher