Re: [PATCH 2/3] Make __float128 use the _Float128 type, PR target/107299

[Segher Boessenkool <segher@kernel.crashing.org>]

On Thu, Dec 15, 2022 at 07:56:14PM +0100, Jakub Jelinek wrote:
> On Thu, Dec 15, 2022 at 12:49:27PM -0600, Segher Boessenkool wrote:
> > Certainly.  But different types with the same mode having different
> > precision is not so very reasonable, and will likely cause other
> > problems as well.
> > 
> > We cannot use precision to order modes or types, that is the core
> > problem.  A conversion from IEEE QP to double-double (or vice versa) is
> > neither widening nor narrowing.
> 
> Sure.  For optabs, I bet we don't necessarily need to care that much, if
> precision is the same, we can ask for widening and narrowing conversion
> and expect only one to be implemented or both doing the same thing between
> such modes.  But when using libcalls, which library function we use is quite
> important because not all of them might be actually implemented in the
> library (better keep doing what we've done before).

I don't think we should name non-widenings widening, or non-narrowings
narrowing.  We should call conversions conversions.

Even if it doesn't cause technical problems the way it is now (of which
I am not convinced at all), faulty names like this are mightily
confusing.  This is a very real *practical* problem :-(


Segher