Refactor ix86_expand_vecop_qihi2.

Since there's regression to use vpermq, and it's manually disabled by
!TARGET_AVX512BW. I remove the codes related to vpermq and make
ix86_expand_vecop_qihi2 only handle vpmovbw + op + vpmovwb case.

gcc/ChangeLog:

	* config/i386/i386-expand.cc (ix86_expand_vecop_qihi2):
	Refactor to avoid redundant TARGET_AVX512BW in many places.

gcc/config/i386/i386-expand.cc

@@ -24864,11 +24864,9 @@ ix86_expand_vecop_qihi2 (enum rtx_code code, rtx dest, rtx op1, rtx op2)
      generic permutation to merge the data back into the right place.  This
      permutation results in VPERMQ, which is slow, so better fall back to
      ix86_expand_vecop_qihi.  */
-  if (!TARGET_AVX512BW)
-    return false;
-
-  if ((qimode == V16QImode && !TARGET_AVX2)
-      || (qimode == V32QImode && (!TARGET_AVX512BW || !TARGET_EVEX512))
+  if (!TARGET_AVX512BW
+      || (qimode == V16QImode && !TARGET_AVX512VL)
+      || (qimode == V32QImode && !TARGET_EVEX512)
       /* There are no V64HImode instructions.  */
       || qimode == V64QImode)
      return false;
@@ -24883,8 +24881,7 @@ ix86_expand_vecop_qihi2 (enum rtx_code code, rtx dest, rtx op1, rtx op2)
     {
     case E_V16QImode:
       himode = V16HImode;
-      if (TARGET_AVX512VL && TARGET_AVX512BW)
-	gen_truncate = gen_truncv16hiv16qi2;
+      gen_truncate = gen_truncv16hiv16qi2;
       break;
     case E_V32QImode:
       himode = V32HImode;
@@ -24926,33 +24923,7 @@ ix86_expand_vecop_qihi2 (enum rtx_code code, rtx dest, rtx op1, rtx op2)
     hdest = expand_simple_binop (himode, code, hop1, hop2,
 				 NULL_RTX, 1, OPTAB_DIRECT);
-  if (gen_truncate)
-    emit_insn (gen_truncate (dest, hdest));
-  else
-    {
-      struct expand_vec_perm_d d;
-      rtx wqdest = gen_reg_rtx (wqimode);
-      rtx wqres = gen_lowpart (wqimode, hdest);
-      bool ok;
-      int i;
-
-      /* Merge the data back into the right place.  */
-      d.target = wqdest;
-      d.op0 = d.op1 = wqres;
-      d.vmode = wqimode;
-      d.nelt = GET_MODE_NUNITS (wqimode);
-      d.one_operand_p = false;
-      d.testing_p = false;
-
-      for (i = 0; i < d.nelt; ++i)
-	d.perm[i] = i * 2;
-
-      ok = ix86_expand_vec_perm_const_1 (&d);
-      gcc_assert (ok);
-
-      emit_move_insn (dest, gen_lowpart (qimode, wqdest));
-    }
-
+  emit_insn (gen_truncate (dest, hdest));
   return true;
 }