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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/101929] [12 Regression] r12-7319 regress x264_r by 4% on
 CLX.
Date: Mon, 07 Mar 2022 07:18:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101929

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 9188d727e33..7f1f12fb6c6 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -2374,7 +2375,7 @@ fail:
                n_vector_builds++;
            }
        }
-      if (all_uniform_p
+      if ((all_uniform_p && !two_operators)
          || n_vector_builds > 1
          || (n_vector_builds =3D=3D children.length ()
              && is_a <gphi *> (stmt_info->stmt)))


will re-enable the vectorization - it evades the vect_construct cost bump
by instead using scalar_to_vec (aka splat) which has not yet been fixed to
account for a possible gpr to xmm move (so it would be a temporary "solutio=
n"
at best).

Another change to mute the effect somewhat (but not fixing x264) that was
mentioned is

diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index b2bf90576d5..acf2cc977b4 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -22595,7 +22595,7 @@ ix86_builtin_vectorization_cost (enum
vect_cost_for_stmt type_of_cost,
       case vec_construct:
        {
          /* N element inserts into SSE vectors.  */
-         int cost =3D TYPE_VECTOR_SUBPARTS (vectype) * ix86_cost->sse_op;
+         int cost =3D (TYPE_VECTOR_SUBPARTS (vectype) - 1) * ix86_cost->ss=
e_op;
          /* One vinserti128 for combining two SSE vectors for AVX256.  */
          if (GET_MODE_BITSIZE (mode) =3D=3D 256)
            cost +=3D ix86_vec_cost (mode, ix86_cost->addss);

which makes sense as the cost of the initial value of the xmm destination is
now costed separately when from GPR and free when from xmm.=