[Bug target/68674] ARM/AARCH64 attribute target neon internal compiler error: in copy_to_mode_reg, at explow.c:595

["chrbr at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68674

--- Comment #12 from chrbr at gcc dot gnu.org ---
(In reply to ktkachov from comment #8)
> (In reply to chrbr from comment #7)
> > I was suggesting in #68934 to make this code invalid and report an error.
> > Since SIMD types should not be used for declarations in NOSIMD context. But
> > I don't have a strong position about this. We might make this code work by
> > repairing the DECL_MODE depending on the usage context, but certainly less
> > practical than handle the error.
> > 
> > Other opinions ?
> > 
> > thanks
> 
> I agree about considering this code invalid.
> In the context where the variables are being declared there is no SIMD, so
> they don't really have a meaning. In the testcase if we wrap the
> declarations in a pargma like so:
> #pragma GCC push_options
> #pragma GCC target ("+simd")
> int8x8_t a, b;
> int16x8_t e;
> #pragma GCC pop_options
> 
> then we don't ICE.
> I suspect repairing DECL_MODE will be a messy affair. So unless you see a
> clean/safe way of doing this I'd propose just somehow detecting this error
> and throwing an error instead of an ICE.

I changed my mind :-) :

- The surrounding of global declaration by the #pragma is too heavy to be used.
The compiler is able to derive the type from the attribute target when using
it.

- The compiler already handle this partially:
 see the comment in stor-layout:
   /* Vector types need to re-check the target flags each time we report
   the machine mode.  We need to do this because attribute target can
   change the result of vector_mode_supported_p and have_regs_of_mode
   on a per-function basis.  Thus the TYPE_MODE of a VECTOR_TYPE can
   change on a per-function basis.  */

I'm testing a central fix in expand_expr. Will need to check on the other
targets but it fixes the case it for arm and aarch64.

patch attached for first feedback and early review.