[gcc(refs/vendors/vrull/heads/slp-improvements)] aarch64: expand VEC_PERM into ins + uzp[12]

[Philipp Tomsich]

https://gcc.gnu.org/g:d61be742513b5b8529ab9ef4022011c471925622

commit d61be742513b5b8529ab9ef4022011c471925622
Author: Manolis Tsamis <manolis.tsamis@vrull.eu>
Date:   Fri Nov 3 14:36:34 2023 +0100

    aarch64: expand VEC_PERM into ins + uzp[12]
    
    The AArch64 backend has specific strategies that can be used to expand
    VEC_PERM expression (see aarch64_expand_vec_perm_const_1).
    
    The last strategy applied if everything else fails is to use a tbl
    instruction, which is known to have very bad latency and performance
    (see aarch64_evpc_tbl). There are various improvements and additions
    that can be done to the reduce the harmful tbl instructions.
    
    The existing mechanisms work for cases that the permute can be done
    with a single existing AArch64 vector instruction, but for x264's
    first loop we need some patterns that may need two vector
    instructions.
    
    On x264, this change results in the following change in instruction
    distribution:
            tbl: 8 -> 0
            ldr: 10 -> 8 (due to the eliminated tbls)
            ins: 8 -> 16
            uzp: 8 -> 16
    A reduction of the newly introduced ins/uzp[12] sequences will be
    addressed in a follow-on change.
    
    Ref #344

Diff:
---
 gcc/config/aarch64/aarch64.cc | 76 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index e6bd3fd0bb4..0f2423ef7de 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -25890,6 +25890,80 @@ aarch64_evpc_ins (struct expand_vec_perm_d *d)
   return true;
 }
 
+/* Recognize patterns suitable for the an INS + UZP.
+   This addresses limited permute optimizations before a more generic search
+   algorithm for two operator sequences is implemented.  */
+static bool
+aarch64_evpc_ins_uzp (struct expand_vec_perm_d *d)
+{
+  machine_mode mode = d->vmode;
+
+  if (d->vec_flags != VEC_ADVSIMD || BYTES_BIG_ENDIAN)
+    return false;
+
+  unsigned HOST_WIDE_INT nelt = d->perm.length ().to_constant ();
+
+  if (nelt != 4
+      || !d->perm[0].is_constant()
+      || !d->perm[1].is_constant()
+      || !d->perm.series_p (0, 2, d->perm[0], 0)
+      || !d->perm.series_p (1, 2, d->perm[1], 0))
+    return false;
+
+  /* We have a {A, B, A, B} permutation.  */
+  HOST_WIDE_INT A = d->perm[0].to_constant ();
+  HOST_WIDE_INT B = d->perm[1].to_constant ();
+
+  if (A >= nelt || B < nelt || d->op0 == d->op1)
+    return false;
+
+  rtx insv;
+  rtx extractv;
+  HOST_WIDE_INT idx, extractindex;
+
+  /* If A is the first element or B is the second element of a UZP1/2 then we
+     can emit this permute as INS + UZP .  */
+  if (A == 0 || A == 1)
+    {
+      insv = d->op0;
+      extractv = d->op1;
+      idx = A == 0 ? 2 : 3;
+      extractindex = B;
+    }
+  else if (B == nelt + 2 || B == nelt + 3)
+    {
+      insv = d->op1;
+      extractv = d->op0;
+      idx = B == nelt + 2 ? 0 : 1;
+      extractindex = A;
+    }
+  else
+    return false;
+
+  if (d->testing_p)
+    return true;
+
+  if (extractindex >= nelt)
+    extractindex -= nelt;
+  gcc_assert (extractindex < nelt);
+
+  /* Emit INS.  */
+  insn_code icode = code_for_aarch64_simd_vec_copy_lane (mode);
+  expand_operand ops[5];
+  create_output_operand (&ops[0], d->target, mode);
+  create_input_operand (&ops[1], insv, mode);
+  create_integer_operand (&ops[2], 1 << idx);
+  create_input_operand (&ops[3], extractv, mode);
+  create_integer_operand (&ops[4], extractindex);
+  expand_insn (icode, 5, ops);
+
+  /* Emit UZP.  */
+  emit_set_insn (d->target, gen_rtx_UNSPEC (mode, gen_rtvec (2, d->target, d->target),
+				      idx & 1 ? UNSPEC_UZP2 : UNSPEC_UZP1));
+
+  return true;
+}
+
 static bool
 aarch64_expand_vec_perm_const_1 (struct expand_vec_perm_d *d)
 {
@@ -25931,6 +26005,8 @@ aarch64_expand_vec_perm_const_1 (struct expand_vec_perm_d *d)
 	    return true;
 	  else if (aarch64_evpc_ins (d))
 	    return true;
+	  else if (aarch64_evpc_ins_uzp (d))
+	    return true;
 	  else if (aarch64_evpc_reencode (d))
 	    return true;