[Bug target/107432] __builtin_convertvector generates inefficient code

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107432

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu.org,
                   |                            |rsandifo at gcc dot gnu.org
             Target|X86_64                      |x86_64-*-*
   Last reconfirmed|                            |2022-10-28
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
            Version|unknown                     |13.0

--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Hongtao.liu from comment #6)
> > Guess expand_vector_conversion can be optimized.
> 
>   if (INTEGRAL_TYPE_P (TREE_TYPE (ret_type))
>       && SCALAR_FLOAT_TYPE_P (TREE_TYPE (arg_type)))
>     code = FIX_TRUNC_EXPR;
>   else if (INTEGRAL_TYPE_P (TREE_TYPE (arg_type))
> 	   && SCALAR_FLOAT_TYPE_P (TREE_TYPE (ret_type)))
>     code = FLOAT_EXPR;
> 
> It only supports floatmn2/fix_truncmn2 for float <-> integer.
> 
> But we can also supports extendmn2/zero_extendmn2/truncmn2 for float <->
> float, integer <-> integer.
> 
> Or are there any concerns and VEC_PACK_TRUNC_EXPR,
> VEC_PACK_FIX_TRUNC_EXPR,VEC_PACK_FLOAT_EXPR are used on purpose?

I think we do support FIX_TRUNC_EXPR or FLOAT_EXPR for float <-> int
conversion of vectors like we now support {CONVERT,NOP}_EXPR for
just widening/shortening.  At least the GIMPLE verifier allows that.

The obtabs would be [us]fix and [us]float, not sure if aarch64 makes use
of those for vector modes or if Richard extended the vectorizer to
consider those (I only remember int <-> int conversions).

So I think if x86_64 can do float <-> int for vectors implementing
[us]fix/[us]float would be the way to go (and of course then make use
of those in lowering/vectorization).