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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/100217] [11/12 Regression] ICE when building valgrind
 testsuite with -march=z14 since r11-7552
Date: Fri, 23 Apr 2021 11:27:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100217

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Ilya Leoshkevich from comment #5)
> That would be an ideal solution, but I wonder how to implement it? Suppose
> we find a way to convince expand to pick FPRX2mode for such a long double.
> What if the following comes up?
>=20
> register long double x asm ("v0");  /* FPRX2mode */
> long double y;                      /* TFmode */
> x +=3D y;                             /* convert? */
>=20
> Would it be feasible to also teach expand to do the mode conversions?

It is certainly doable, but perhaps with extra target hooks or something
similar.
Types have their TYPE_MODE and decls have DECL_MODE, though the question is
what breaks if TYPE_MODE !=3D DECL_MODE, at least the comment in tree.h say=
s that
they can only differ for FIELD_DECLs.  Anyway, in GIMPLE register vars are
non-SSA, so apart from inline asm one needs separate loads and stores to th=
em,
so if we could expand those as having FPRX2 hard reg and loads from it conv=
ert
to TFmode and stores into it convert from TFmode, ...

> One other alternative might be to detect `register long double asm("fN")`
> declarations and go back to using floating point register pairs for
> functions that contain them.

But this might be actually best short-time solution (for GCC 11.x).=