This backport contains 2 patchs from gcc main stream tree.
The commit id of these patchs list as following in the order of time.

0001-AArch64-Improve-SVE-constant-moves.patch
4aeb1ba7f62c1d680c819ae3e137c3bad6f520ca

0002-aarch64-Add-vector-vector-vec_extract-patterns-PR928.patch
c15893df6eafc32efd6184379dd7f02c36da7d12

diff -Nurp a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
--- a/gcc/config/aarch64/aarch64.c	2020-09-03 19:50:00.484000000 +0800
+++ b/gcc/config/aarch64/aarch64.c	2020-09-03 19:50:19.336943210 +0800
@@ -3632,7 +3632,7 @@ aarch64_maybe_expand_sve_subreg_move (rt
    attributes.  Unlike gen_lowpart, this doesn't care whether the
    mode change is valid.  */
 
-static rtx
+rtx
 aarch64_replace_reg_mode (rtx x, machine_mode mode)
 {
   if (GET_MODE (x) == mode)
@@ -15016,6 +15016,36 @@ aarch64_simd_check_vect_par_cnst_half (r
   return true;
 }
 
+/* Return a PARALLEL containing NELTS elements, with element I equal
+   to BASE + I * STEP.  */
+
+rtx
+aarch64_gen_stepped_int_parallel (unsigned int nelts, int base, int step)
+{
+  rtvec vec = rtvec_alloc (nelts);
+  for (unsigned int i = 0; i < nelts; ++i)
+    RTVEC_ELT (vec, i) = gen_int_mode (base + i * step, DImode);
+  return gen_rtx_PARALLEL (VOIDmode, vec);
+}
+
+/* Return true if OP is a PARALLEL of CONST_INTs that form a linear
+   series with step STEP.  */
+
+bool
+aarch64_stepped_int_parallel_p (rtx op, int step)
+{
+  if (GET_CODE (op) != PARALLEL || !CONST_INT_P (XVECEXP (op, 0, 0)))
+    return false;
+
+  unsigned HOST_WIDE_INT base = UINTVAL (XVECEXP (op, 0, 0));
+  for (int i = 1; i < XVECLEN (op, 0); ++i)
+    if (!CONST_INT_P (XVECEXP (op, 0, i))
+	|| UINTVAL (XVECEXP (op, 0, i)) != base + i * step)
+      return false;
+
+  return true;
+}
+
 /* Bounds-check lanes.  Ensure OPERAND lies between LOW (inclusive) and
    HIGH (exclusive).  */
 void
diff -Nurp a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
--- a/gcc/config/aarch64/aarch64-protos.h	2020-09-03 19:50:00.484000000 +0800
+++ b/gcc/config/aarch64/aarch64-protos.h	2020-09-03 19:50:29.137683100 +0800
@@ -501,6 +501,8 @@ bool aarch64_sve_ld1r_operand_p (rtx);
 bool aarch64_sve_ldr_operand_p (rtx);
 bool aarch64_sve_struct_memory_operand_p (rtx);
 rtx aarch64_simd_vect_par_cnst_half (machine_mode, int, bool);
+rtx aarch64_gen_stepped_int_parallel (unsigned int, int, int);
+bool aarch64_stepped_int_parallel_p (rtx, int);
 rtx aarch64_tls_get_addr (void);
 tree aarch64_fold_builtin (tree, int, tree *, bool);
 unsigned aarch64_dbx_register_number (unsigned);
@@ -516,6 +518,7 @@ void aarch64_expand_mov_immediate (rtx,
 void aarch64_emit_sve_pred_move (rtx, rtx, rtx);
 void aarch64_expand_sve_mem_move (rtx, rtx, machine_mode);
 bool aarch64_maybe_expand_sve_subreg_move (rtx, rtx);
+rtx aarch64_replace_reg_mode (rtx, machine_mode);
 void aarch64_split_sve_subreg_move (rtx, rtx, rtx);
 void aarch64_expand_prologue (void);
 void aarch64_expand_vector_init (rtx, rtx);
diff -Nurp a/gcc/config/aarch64/aarch64-simd.md b/gcc/config/aarch64/aarch64-simd.md
--- a/gcc/config/aarch64/aarch64-simd.md	2020-09-03 19:50:00.484000000 +0800
+++ b/gcc/config/aarch64/aarch64-simd.md	2020-09-03 19:50:44.100673150 +0800
@@ -282,37 +282,51 @@
         rtx dst_high_part = gen_highpart (<VHALF>mode, dst);
 	rtx lo = aarch64_simd_vect_par_cnst_half (<MODE>mode, <nunits>, false);
 	rtx hi = aarch64_simd_vect_par_cnst_half (<MODE>mode, <nunits>, true);
-
-        emit_insn
-          (gen_aarch64_simd_mov_from_<mode>low (dst_low_part, src, lo));
-        emit_insn
-          (gen_aarch64_simd_mov_from_<mode>high (dst_high_part, src, hi));
+        emit_insn (gen_aarch64_get_half<mode> (dst_low_part, src, lo));
+        emit_insn (gen_aarch64_get_half<mode> (dst_high_part, src, hi));
       }
     DONE;
   }
 )
 
-(define_insn "aarch64_simd_mov_from_<mode>low"
-  [(set (match_operand:<VHALF> 0 "register_operand" "=r")
+(define_expand "aarch64_get_half<mode>"
+  [(set (match_operand:<VHALF> 0 "register_operand")
         (vec_select:<VHALF>
-          (match_operand:VQ 1 "register_operand" "w")
-          (match_operand:VQ 2 "vect_par_cnst_lo_half" "")))]
-  "TARGET_SIMD && reload_completed"
-  "umov\t%0, %1.d[0]"
-  [(set_attr "type" "neon_to_gp<q>")
-   (set_attr "length" "4")
-  ])
+          (match_operand:VQ 1 "register_operand")
+          (match_operand 2 "ascending_int_parallel")))]
+  "TARGET_SIMD"
+)
+
+(define_insn_and_split "aarch64_simd_mov_from_<mode>low"
+  [(set (match_operand:<VHALF> 0 "register_operand" "=w,?r")
+        (vec_select:<VHALF>
+          (match_operand:VQ_NO2E 1 "register_operand" "w,w")
+          (match_operand:VQ_NO2E 2 "vect_par_cnst_lo_half" "")))]
+  "TARGET_SIMD"
+  "@
+   #
+   umov\t%0, %1.d[0]"
+  "&& reload_completed && aarch64_simd_register (operands[0], <VHALF>mode)"
+  [(set (match_dup 0) (match_dup 1))]
+  {
+    operands[1] = aarch64_replace_reg_mode (operands[1], <VHALF>mode);
+  }
+  [(set_attr "type" "mov_reg,neon_to_gp<q>")
+   (set_attr "length" "4")]
+)
 
 (define_insn "aarch64_simd_mov_from_<mode>high"
-  [(set (match_operand:<VHALF> 0 "register_operand" "=r")
+  [(set (match_operand:<VHALF> 0 "register_operand" "=w,?r")
         (vec_select:<VHALF>
-          (match_operand:VQ 1 "register_operand" "w")
-          (match_operand:VQ 2 "vect_par_cnst_hi_half" "")))]
-  "TARGET_SIMD && reload_completed"
-  "umov\t%0, %1.d[1]"
-  [(set_attr "type" "neon_to_gp<q>")
-   (set_attr "length" "4")
-  ])
+          (match_operand:VQ_NO2E 1 "register_operand" "w,w")
+          (match_operand:VQ_NO2E 2 "vect_par_cnst_hi_half" "")))]
+  "TARGET_SIMD"
+  "@
+   dup\\t%d0, %1.d[1]
+   umov\t%0, %1.d[1]"
+  [(set_attr "type" "neon_dup<q>,neon_to_gp<q>")
+   (set_attr "length" "4")]
+)
 
 (define_insn "orn<mode>3"
  [(set (match_operand:VDQ_I 0 "register_operand" "=w")
@@ -6016,6 +6030,35 @@
     DONE;
 })
 
+;; Extract a 64-bit vector from one half of a 128-bit vector.
+(define_expand "vec_extract<mode><Vhalf>"
+  [(match_operand:<VHALF> 0 "register_operand")
+   (match_operand:VQ_NO2E 1 "register_operand")
+   (match_operand 2 "immediate_operand")]
+  "TARGET_SIMD"
+{
+  int start = INTVAL (operands[2]);
+  if (start != 0 && start != <nunits> / 2)
+    FAIL;
+  rtx sel = aarch64_gen_stepped_int_parallel (<nunits> / 2, start, 1);
+  emit_insn (gen_aarch64_get_half<mode> (operands[0], operands[1], sel));
+  DONE;
+})
+
+;; Extract a single-element 64-bit vector from one half of a 128-bit vector.
+(define_expand "vec_extractv2dfv1df"
+  [(match_operand:V1DF 0 "register_operand")
+   (match_operand:V2DF 1 "register_operand")
+   (match_operand 2 "immediate_operand")]
+  "TARGET_SIMD"
+{
+  /* V1DF is rarely used by other patterns, so it should be better to hide
+     it in a subreg destination of a normal DF op.  */
+  rtx scalar0 = gen_lowpart (DFmode, operands[0]);
+  emit_insn (gen_vec_extractv2dfdf (scalar0, operands[1], operands[2]));
+  DONE;
+})
+
 ;; aes
 
 (define_insn "aarch64_crypto_aes<aes_op>v16qi"
diff -Nurp a/gcc/config/aarch64/predicates.md b/gcc/config/aarch64/predicates.md
--- a/gcc/config/aarch64/predicates.md	2020-09-03 19:50:00.484000000 +0800
+++ b/gcc/config/aarch64/predicates.md	2020-09-03 19:50:49.315344350 +0800
@@ -438,6 +438,12 @@
   return aarch64_simd_check_vect_par_cnst_half (op, mode, false);
 })
 
+(define_predicate "ascending_int_parallel"
+  (match_code "parallel")
+{
+  return aarch64_stepped_int_parallel_p (op, 1);
+})
+
 (define_special_predicate "aarch64_simd_lshift_imm"
   (match_code "const,const_vector")
 {