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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/107432] __builtin_convertvector generates inefficient
 code
Date: Fri, 28 Oct 2022 03:36:53 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107432

--- Comment #4 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Hongtao.liu from comment #3)
> typedef int v4si __attribute__((vector_size(16)));
> typedef long long v4di __attribute__((vector_size(32)));
>=20
> v4si
> foo (v4di a)
> {
>     return __builtin_convertvector (a, v4si);
> }
>=20
> hmm, we actually support truncv4div4si2, but some how gcc failed to gener=
ate
> .VEC_CONVERT with truncmn2.
>=20

/* IFN_VEC_CONVERT is supposed to be expanded at pass_lower_vector.  So this
   dummy function should never be called.  */

static void
expand_VEC_CONVERT (internal_fn, gcall *)
{
  gcc_unreachable ();
}

It's lowered by pass_lower_vector, ideally, can we use truncmn2 in
expand_VEC_CONVERT if src is bigger integer mode than dest.=