diff --git a/gcc/builtins.c b/gcc/builtins.c
index 845a8bb1201..cddef63cfc2 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -3119,13 +3119,16 @@ expand_builtin_strnlen (tree exp, rtx target, machine_mode target_mode)
 
 static rtx
 builtin_memcpy_read_str (void *data, void *, HOST_WIDE_INT offset,
-			 scalar_int_mode mode)
+			 fixed_size_mode mode)
 {
   /* The REPresentation pointed to by DATA need not be a nul-terminated
      string but the caller guarantees it's large enough for MODE.  */
   const char *rep = (const char *) data;
 
-  return c_readstr (rep + offset, mode, /*nul_terminated=*/false);
+  /* The by-pieces infrastructure does not try to pick a vector mode
+     for memcpy expansion.  */
+  return c_readstr (rep + offset, as_a <scalar_int_mode> (mode),
+		    /*nul_terminated=*/false);
 }
 
 /* LEN specify length of the block of memcpy/memset operation.
@@ -3742,14 +3745,16 @@ expand_builtin_stpncpy (tree exp, rtx)
 
 rtx
 builtin_strncpy_read_str (void *data, void *, HOST_WIDE_INT offset,
-			  scalar_int_mode mode)
+			  fixed_size_mode mode)
 {
   const char *str = (const char *) data;
 
   if ((unsigned HOST_WIDE_INT) offset > strlen (str))
     return const0_rtx;
 
-  return c_readstr (str + offset, mode);
+  /* The by-pieces infrastructure does not try to pick a vector mode
+     for strncpy expansion.  */
+  return c_readstr (str + offset, as_a <scalar_int_mode> (mode));
 }
 
 /* Helper to check the sizes of sequences and the destination of calls
@@ -3950,30 +3955,125 @@ expand_builtin_strncpy (tree exp, rtx target)
   return NULL_RTX;
 }
 
-/* Callback routine for store_by_pieces.  Read GET_MODE_BITSIZE (MODE)
-   bytes from constant string DATA + OFFSET and return it as target
-   constant.  If PREV isn't nullptr, it has the RTL info from the
+/* Return the RTL of a register in MODE generated from PREV in the
    previous iteration.  */
 
-rtx
-builtin_memset_read_str (void *data, void *prevp,
-			 HOST_WIDE_INT offset ATTRIBUTE_UNUSED,
-			 scalar_int_mode mode)
+static rtx
+gen_memset_value_from_prev (by_pieces_prev *prev, fixed_size_mode mode)
 {
-  by_pieces_prev *prev = (by_pieces_prev *) prevp;
+  rtx target = nullptr;
   if (prev != nullptr && prev->data != nullptr)
     {
       /* Use the previous data in the same mode.  */
       if (prev->mode == mode)
 	return prev->data;
+
+      fixed_size_mode prev_mode = prev->mode;
+
+      /* Don't use the previous data to write QImode if it is in a
+	 vector mode.  */
+      if (VECTOR_MODE_P (prev_mode) && mode == QImode)
+	return target;
+
+      rtx prev_rtx = prev->data;
+
+      if (REG_P (prev_rtx)
+	  && HARD_REGISTER_P (prev_rtx)
+	  && lowpart_subreg_regno (REGNO (prev_rtx), prev_mode, mode) < 0)
+	{
+	  /* This case occurs when PREV_MODE is a vector and when
+	     MODE is too small to store using vector operations.
+	     After register allocation, the code will need to move the
+	     lowpart of the vector register into a non-vector register.
+
+	     Also, the target has chosen to use a hard register
+	     instead of going with the default choice of using a
+	     pseudo register.  We should respect that choice and try to
+	     avoid creating a pseudo register with the same mode as the
+	     current hard register.
+
+	     In principle, we could just use a lowpart MODE subreg of
+	     the vector register.  However, the vector register mode might
+	     be too wide for non-vector registers, and we already know
+	     that the non-vector mode is too small for vector registers.
+	     It's therefore likely that we'd need to spill to memory in
+	     the vector mode and reload the non-vector value from there.
+
+	     Try to avoid that by reducing the vector register to the
+	     smallest size that it can hold.  This should increase the
+	     chances that non-vector registers can hold both the inner
+	     and outer modes of the subreg that we generate later.  */
+	  machine_mode m;
+	  fixed_size_mode candidate;
+	  FOR_EACH_MODE_IN_CLASS (m, GET_MODE_CLASS (mode))
+	    if (is_a<fixed_size_mode> (m, &candidate))
+	      {
+		if (GET_MODE_SIZE (candidate)
+		    >= GET_MODE_SIZE (prev_mode))
+		  break;
+		if (GET_MODE_SIZE (candidate) >= GET_MODE_SIZE (mode)
+		    && lowpart_subreg_regno (REGNO (prev_rtx),
+					     prev_mode, candidate) >= 0)
+		  {
+		    target = lowpart_subreg (candidate, prev_rtx,
+					     prev_mode);
+		    prev_rtx = target;
+		    prev_mode = candidate;
+		    break;
+		  }
+	      }
+	  if (target == nullptr)
+	    prev_rtx = copy_to_reg (prev_rtx);
+	}
+
+      target = lowpart_subreg (mode, prev_rtx, prev_mode);
     }
+  return target;
+}
+
+/* Callback routine for store_by_pieces.  Read GET_MODE_BITSIZE (MODE)
+   bytes from constant string DATA + OFFSET and return it as target
+   constant.  If PREV isn't nullptr, it has the RTL info from the
+   previous iteration.  */
 
+rtx
+builtin_memset_read_str (void *data, void *prev,
+			 HOST_WIDE_INT offset ATTRIBUTE_UNUSED,
+			 fixed_size_mode mode)
+{
   const char *c = (const char *) data;
-  char *p = XALLOCAVEC (char, GET_MODE_SIZE (mode));
+  unsigned int size = GET_MODE_SIZE (mode);
 
-  memset (p, *c, GET_MODE_SIZE (mode));
+  rtx target = gen_memset_value_from_prev ((by_pieces_prev *) prev,
+					   mode);
+  if (target != nullptr)
+    return target;
+  rtx src = gen_int_mode (*c, QImode);
 
-  return c_readstr (p, mode);
+  if (VECTOR_MODE_P (mode))
+    {
+      gcc_assert (GET_MODE_INNER (mode) == QImode);
+
+      rtx const_vec = gen_const_vec_duplicate (mode, src);
+      if (prev == NULL)
+	/* Return CONST_VECTOR when called by a query function.  */
+	target = const_vec;
+      else
+	{
+	  /* Use the move expander with CONST_VECTOR.  */
+	  target = targetm.gen_memset_scratch_rtx (mode);
+	  emit_move_insn (target, const_vec);
+	}
+
+      return target;
+    }
+
+  char *p = XALLOCAVEC (char, size);
+
+  memset (p, *c, size);
+
+  /* Vector modes should be handled above.  */
+  return c_readstr (p, as_a <scalar_int_mode> (mode));
 }
 
 /* Callback routine for store_by_pieces.  Return the RTL of a register
@@ -3983,33 +4083,45 @@ builtin_memset_read_str (void *data, void *prevp,
    nullptr, it has the RTL info from the previous iteration.  */
 
 static rtx
-builtin_memset_gen_str (void *data, void *prevp,
+builtin_memset_gen_str (void *data, void *prev,
 			HOST_WIDE_INT offset ATTRIBUTE_UNUSED,
-			scalar_int_mode mode)
+			fixed_size_mode mode)
 {
   rtx target, coeff;
   size_t size;
   char *p;
 
-  by_pieces_prev *prev = (by_pieces_prev *) prevp;
-  if (prev != nullptr && prev->data != nullptr)
-    {
-      /* Use the previous data in the same mode.  */
-      if (prev->mode == mode)
-	return prev->data;
-
-      target = simplify_gen_subreg (mode, prev->data, prev->mode, 0);
-      if (target != nullptr)
-	return target;
-    }
-
   size = GET_MODE_SIZE (mode);
   if (size == 1)
     return (rtx) data;
 
+  target = gen_memset_value_from_prev ((by_pieces_prev *) prev, mode);
+  if (target != nullptr)
+    return target;
+
+  if (VECTOR_MODE_P (mode))
+    {
+      gcc_assert (GET_MODE_INNER (mode) == QImode);
+
+      /* vec_duplicate_optab is a precondition to pick a vector mode for
+	 the memset expander.  */
+      insn_code icode = optab_handler (vec_duplicate_optab, mode);
+
+      target = targetm.gen_memset_scratch_rtx (mode);
+      class expand_operand ops[2];
+      create_output_operand (&ops[0], target, mode);
+      create_input_operand (&ops[1], (rtx) data, QImode);
+      expand_insn (icode, 2, ops);
+      if (!rtx_equal_p (target, ops[0].value))
+	emit_move_insn (target, ops[0].value);
+
+      return target;
+    }
+
   p = XALLOCAVEC (char, size);
   memset (p, 1, size);
-  coeff = c_readstr (p, mode);
+  /* Vector modes should be handled above.  */
+  coeff = c_readstr (p, as_a <scalar_int_mode> (mode));
 
   target = convert_to_mode (mode, (rtx) data, 1);
   target = expand_mult (mode, target, coeff, NULL_RTX, 1);
@@ -4113,7 +4225,7 @@ try_store_by_multiple_pieces (rtx to, rtx len, unsigned int ctz_len,
 			    &valc, align, true))
     return false;
 
-  rtx (*constfun) (void *, void *, HOST_WIDE_INT, scalar_int_mode);
+  by_pieces_constfn constfun;
   void *constfundata;
   if (val)
     {
diff --git a/gcc/builtins.h b/gcc/builtins.h
index b580635a09f..024ddbfa704 100644
--- a/gcc/builtins.h
+++ b/gcc/builtins.h
@@ -111,9 +111,9 @@ extern tree mathfn_built_in (tree, enum built_in_function fn);
 extern tree mathfn_built_in (tree, combined_fn);
 extern tree mathfn_built_in_type (combined_fn);
 extern rtx builtin_strncpy_read_str (void *, void *, HOST_WIDE_INT,
-				     scalar_int_mode);
+				     fixed_size_mode);
 extern rtx builtin_memset_read_str (void *, void *, HOST_WIDE_INT,
-				    scalar_int_mode);
+				    fixed_size_mode);
 extern rtx expand_builtin_saveregs (void);
 extern tree std_build_builtin_va_list (void);
 extern tree std_fn_abi_va_list (tree);
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index a464d268a12..cb015283237 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -12158,6 +12158,13 @@ This function prepares to emit a conditional comparison within a sequence
  @var{bit_code} is @code{AND} or @code{IOR}, which is the op on the compares.
 @end deftypefn
 
+@deftypefn {Target Hook} rtx TARGET_GEN_MEMSET_SCRATCH_RTX (machine_mode @var{mode})
+This hook should return an rtx for a scratch register in @var{mode} to
+be used when expanding memset calls.  The backend can use a hard scratch
+register to avoid stack realignment when expanding memset.  The default
+is @code{gen_reg_rtx}.
+@end deftypefn
+
 @deftypefn {Target Hook} unsigned TARGET_LOOP_UNROLL_ADJUST (unsigned @var{nunroll}, class loop *@var{loop})
 This target hook returns a new value for the number of times @var{loop}
 should be unrolled. The parameter @var{nunroll} is the number of times
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 0b603423985..4a522ae7e2e 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -7986,6 +7986,8 @@ lists.
 
 @hook TARGET_GEN_CCMP_NEXT
 
+@hook TARGET_GEN_MEMSET_SCRATCH_RTX
+
 @hook TARGET_LOOP_UNROLL_ADJUST
 
 @defmac POWI_MAX_MULTS
diff --git a/gcc/expr.c b/gcc/expr.c
index 6a4368113c4..b65cfcfdcd1 100644
--- a/gcc/expr.c
+++ b/gcc/expr.c
@@ -769,15 +769,36 @@ alignment_for_piecewise_move (unsigned int max_pieces, unsigned int align)
   return align;
 }
 
-/* Return the widest integer mode that is narrower than SIZE bytes.  */
+/* Return the widest QI vector, if QI_MODE is true, or integer mode
+   that is narrower than SIZE bytes.  */
 
-static scalar_int_mode
-widest_int_mode_for_size (unsigned int size)
+static fixed_size_mode
+widest_fixed_size_mode_for_size (unsigned int size, bool qi_vector)
 {
-  scalar_int_mode result = NARROWEST_INT_MODE;
+  fixed_size_mode result = NARROWEST_INT_MODE;
 
   gcc_checking_assert (size > 1);
 
+  /* Use QI vector only if size is wider than a WORD.  */
+  if (qi_vector && size > UNITS_PER_WORD)
+    {
+      machine_mode mode;
+      fixed_size_mode candidate;
+      FOR_EACH_MODE_IN_CLASS (mode, MODE_VECTOR_INT)
+	if (is_a<fixed_size_mode> (mode, &candidate)
+	    && GET_MODE_INNER (candidate) == QImode)
+	  {
+	    if (GET_MODE_SIZE (candidate) >= size)
+	      break;
+	    if (optab_handler (vec_duplicate_optab, candidate)
+		!= CODE_FOR_nothing)
+	      result = candidate;
+	  }
+
+      if (result != NARROWEST_INT_MODE)
+	return result;
+    }
+
   opt_scalar_int_mode tmode;
   FOR_EACH_MODE_IN_CLASS (tmode, MODE_INT)
     if (GET_MODE_SIZE (tmode.require ()) < size)
@@ -815,13 +836,14 @@ by_pieces_ninsns (unsigned HOST_WIDE_INT l, unsigned int align,
 		  unsigned int max_size, by_pieces_operation op)
 {
   unsigned HOST_WIDE_INT n_insns = 0;
-  scalar_int_mode mode;
+  fixed_size_mode mode;
 
   if (targetm.overlap_op_by_pieces_p () && op != COMPARE_BY_PIECES)
     {
       /* NB: Round up L and ALIGN to the widest integer mode for
 	 MAX_SIZE.  */
-      mode = widest_int_mode_for_size (max_size);
+      mode = widest_fixed_size_mode_for_size (max_size,
+					      op == SET_BY_PIECES);
       if (optab_handler (mov_optab, mode) != CODE_FOR_nothing)
 	{
 	  unsigned HOST_WIDE_INT up = ROUND_UP (l, GET_MODE_SIZE (mode));
@@ -835,7 +857,8 @@ by_pieces_ninsns (unsigned HOST_WIDE_INT l, unsigned int align,
 
   while (max_size > 1 && l > 0)
     {
-      mode = widest_int_mode_for_size (max_size);
+      mode = widest_fixed_size_mode_for_size (max_size,
+					      op == SET_BY_PIECES);
       enum insn_code icode;
 
       unsigned int modesize = GET_MODE_SIZE (mode);
@@ -903,8 +926,7 @@ class pieces_addr
   void *m_cfndata;
 public:
   pieces_addr (rtx, bool, by_pieces_constfn, void *);
-  rtx adjust (scalar_int_mode, HOST_WIDE_INT,
-	      by_pieces_prev * = nullptr);
+  rtx adjust (fixed_size_mode, HOST_WIDE_INT, by_pieces_prev * = nullptr);
   void increment_address (HOST_WIDE_INT);
   void maybe_predec (HOST_WIDE_INT);
   void maybe_postinc (HOST_WIDE_INT);
@@ -1006,7 +1028,7 @@ pieces_addr::decide_autoinc (machine_mode ARG_UNUSED (mode), bool reverse,
    but we still modify the MEM's properties.  */
 
 rtx
-pieces_addr::adjust (scalar_int_mode mode, HOST_WIDE_INT offset,
+pieces_addr::adjust (fixed_size_mode mode, HOST_WIDE_INT offset,
 		     by_pieces_prev *prev)
 {
   if (m_constfn)
@@ -1060,11 +1082,14 @@ pieces_addr::maybe_postinc (HOST_WIDE_INT size)
 class op_by_pieces_d
 {
  private:
-  scalar_int_mode get_usable_mode (scalar_int_mode mode, unsigned int);
+  fixed_size_mode get_usable_mode (fixed_size_mode, unsigned int);
+  fixed_size_mode smallest_fixed_size_mode_for_size (unsigned int);
 
  protected:
   pieces_addr m_to, m_from;
-  unsigned HOST_WIDE_INT m_len;
+  /* Make m_len read-only so that smallest_fixed_size_mode_for_size can
+     use it to check the valid mode size.  */
+  const unsigned HOST_WIDE_INT m_len;
   HOST_WIDE_INT m_offset;
   unsigned int m_align;
   unsigned int m_max_size;
@@ -1073,6 +1098,8 @@ class op_by_pieces_d
   bool m_push;
   /* True if targetm.overlap_op_by_pieces_p () returns true.  */
   bool m_overlap_op_by_pieces;
+  /* True if QI vector mode can be used.  */
+  bool m_qi_vector_mode;
 
   /* Virtual functions, overriden by derived classes for the specific
      operation.  */
@@ -1084,7 +1111,8 @@ class op_by_pieces_d
 
  public:
   op_by_pieces_d (rtx, bool, rtx, bool, by_pieces_constfn, void *,
-		  unsigned HOST_WIDE_INT, unsigned int, bool);
+		  unsigned HOST_WIDE_INT, unsigned int, bool,
+		  bool = false);
   void run ();
 };
 
@@ -1099,11 +1127,12 @@ op_by_pieces_d::op_by_pieces_d (rtx to, bool to_load,
 				by_pieces_constfn from_cfn,
 				void *from_cfn_data,
 				unsigned HOST_WIDE_INT len,
-				unsigned int align, bool push)
+				unsigned int align, bool push,
+				bool qi_vector_mode)
   : m_to (to, to_load, NULL, NULL),
     m_from (from, from_load, from_cfn, from_cfn_data),
     m_len (len), m_max_size (MOVE_MAX_PIECES + 1),
-    m_push (push)
+    m_push (push), m_qi_vector_mode (qi_vector_mode)
 {
   int toi = m_to.get_addr_inc ();
   int fromi = m_from.get_addr_inc ();
@@ -1124,7 +1153,9 @@ op_by_pieces_d::op_by_pieces_d (rtx to, bool to_load,
   if (by_pieces_ninsns (len, align, m_max_size, MOVE_BY_PIECES) > 2)
     {
       /* Find the mode of the largest comparison.  */
-      scalar_int_mode mode = widest_int_mode_for_size (m_max_size);
+      fixed_size_mode mode
+	= widest_fixed_size_mode_for_size (m_max_size,
+					   m_qi_vector_mode);
 
       m_from.decide_autoinc (mode, m_reverse, len);
       m_to.decide_autoinc (mode, m_reverse, len);
@@ -1139,8 +1170,8 @@ op_by_pieces_d::op_by_pieces_d (rtx to, bool to_load,
 /* This function returns the largest usable integer mode for LEN bytes
    whose size is no bigger than size of MODE.  */
 
-scalar_int_mode
-op_by_pieces_d::get_usable_mode (scalar_int_mode mode, unsigned int len)
+fixed_size_mode
+op_by_pieces_d::get_usable_mode (fixed_size_mode mode, unsigned int len)
 {
   unsigned int size;
   do
@@ -1148,13 +1179,42 @@ op_by_pieces_d::get_usable_mode (scalar_int_mode mode, unsigned int len)
       size = GET_MODE_SIZE (mode);
       if (len >= size && prepare_mode (mode, m_align))
 	break;
-      /* NB: widest_int_mode_for_size checks SIZE > 1.  */
-      mode = widest_int_mode_for_size (size);
+      /* widest_fixed_size_mode_for_size checks SIZE > 1.  */
+      mode = widest_fixed_size_mode_for_size (size, m_qi_vector_mode);
     }
   while (1);
   return mode;
 }
 
+/* Return the smallest integer or QI vector mode that is not narrower
+   than SIZE bytes.  */
+
+fixed_size_mode
+op_by_pieces_d::smallest_fixed_size_mode_for_size (unsigned int size)
+{
+  /* Use QI vector only for > size of WORD.  */
+  if (m_qi_vector_mode && size > UNITS_PER_WORD)
+    {
+      machine_mode mode;
+      fixed_size_mode candidate;
+      FOR_EACH_MODE_IN_CLASS (mode, MODE_VECTOR_INT)
+	if (is_a<fixed_size_mode> (mode, &candidate)
+	    && GET_MODE_INNER (candidate) == QImode)
+	  {
+	    /* Don't return a mode wider than M_LEN.  */
+	    if (GET_MODE_SIZE (candidate) > m_len)
+	      break;
+
+	    if (GET_MODE_SIZE (candidate) >= size
+		&& (optab_handler (vec_duplicate_optab, candidate)
+		    != CODE_FOR_nothing))
+	      return candidate;
+	  }
+    }
+
+  return smallest_int_mode_for_size (size * BITS_PER_UNIT);
+}
+
 /* This function contains the main loop used for expanding a block
    operation.  First move what we can in the largest integer mode,
    then go to successively smaller modes.  For every access, call
@@ -1166,9 +1226,12 @@ op_by_pieces_d::run ()
   if (m_len == 0)
     return;
 
-  /* NB: widest_int_mode_for_size checks M_MAX_SIZE > 1.  */
-  scalar_int_mode mode = widest_int_mode_for_size (m_max_size);
-  mode = get_usable_mode (mode, m_len);
+  unsigned HOST_WIDE_INT length = m_len;
+
+  /* widest_fixed_size_mode_for_size checks M_MAX_SIZE > 1.  */
+  fixed_size_mode mode
+    = widest_fixed_size_mode_for_size (m_max_size, m_qi_vector_mode);
+  mode = get_usable_mode (mode, length);
 
   by_pieces_prev to_prev = { nullptr, mode };
   by_pieces_prev from_prev = { nullptr, mode };
@@ -1178,7 +1241,7 @@ op_by_pieces_d::run ()
       unsigned int size = GET_MODE_SIZE (mode);
       rtx to1 = NULL_RTX, from1;
 
-      while (m_len >= size)
+      while (length >= size)
 	{
 	  if (m_reverse)
 	    m_offset -= size;
@@ -1201,22 +1264,22 @@ op_by_pieces_d::run ()
 	  if (!m_reverse)
 	    m_offset += size;
 
-	  m_len -= size;
+	  length -= size;
 	}
 
       finish_mode (mode);
 
-      if (m_len == 0)
+      if (length == 0)
 	return;
 
       if (!m_push && m_overlap_op_by_pieces)
 	{
 	  /* NB: Generate overlapping operations if it is not a stack
 	     push since stack push must not overlap.  Get the smallest
-	     integer mode for M_LEN bytes.  */
-	  mode = smallest_int_mode_for_size (m_len * BITS_PER_UNIT);
+	     fixed size mode for M_LEN bytes.  */
+	  mode = smallest_fixed_size_mode_for_size (length);
 	  mode = get_usable_mode (mode, GET_MODE_SIZE (mode));
-	  int gap = GET_MODE_SIZE (mode) - m_len;
+	  int gap = GET_MODE_SIZE (mode) - length;
 	  if (gap > 0)
 	    {
 	      /* If size of MODE > M_LEN, generate the last operation
@@ -1226,20 +1289,21 @@ op_by_pieces_d::run ()
 		m_offset += gap;
 	      else
 		m_offset -= gap;
-	      m_len += gap;
+	      length += gap;
 	    }
 	}
       else
 	{
-	  /* NB: widest_int_mode_for_size checks SIZE > 1.  */
-	  mode = widest_int_mode_for_size (size);
-	  mode = get_usable_mode (mode, m_len);
+	  /* widest_fixed_size_mode_for_size checks SIZE > 1.  */
+	  mode = widest_fixed_size_mode_for_size (size,
+						  m_qi_vector_mode);
+	  mode = get_usable_mode (mode, length);
 	}
     }
   while (1);
 
   /* The code above should have handled everything.  */
-  gcc_assert (!m_len);
+  gcc_assert (!length);
 }
 
 /* Derived class from op_by_pieces_d, providing support for block move
@@ -1355,9 +1419,10 @@ class store_by_pieces_d : public op_by_pieces_d
 
  public:
   store_by_pieces_d (rtx to, by_pieces_constfn cfn, void *cfn_data,
-		     unsigned HOST_WIDE_INT len, unsigned int align)
+		     unsigned HOST_WIDE_INT len, unsigned int align,
+		     bool qi_vector_mode)
     : op_by_pieces_d (to, false, NULL_RTX, true, cfn, cfn_data, len,
-		      align, false)
+		      align, false, qi_vector_mode)
   {
   }
   rtx finish_retmode (memop_ret);
@@ -1446,7 +1511,8 @@ can_store_by_pieces (unsigned HOST_WIDE_INT len,
       max_size = STORE_MAX_PIECES + 1;
       while (max_size > 1 && l > 0)
 	{
-	  scalar_int_mode mode = widest_int_mode_for_size (max_size);
+	  fixed_size_mode mode
+	    = widest_fixed_size_mode_for_size (max_size, memsetp);
 
 	  icode = optab_handler (mov_optab, mode);
 	  if (icode != CODE_FOR_nothing
@@ -1460,7 +1526,11 @@ can_store_by_pieces (unsigned HOST_WIDE_INT len,
 		    offset -= size;
 
 		  cst = (*constfun) (constfundata, nullptr, offset, mode);
-		  if (!targetm.legitimate_constant_p (mode, cst))
+		  /* All CONST_VECTORs can be loaded for memset since
+		     vec_duplicate_optab is a precondition to pick a
+		     vector mode for the memset expander.  */
+		  if (!((memsetp && VECTOR_MODE_P (mode))
+			|| targetm.legitimate_constant_p (mode, cst)))
 		    return 0;
 
 		  if (!reverse)
@@ -1504,7 +1574,8 @@ store_by_pieces (rtx to, unsigned HOST_WIDE_INT len,
 		 memsetp ? SET_BY_PIECES : STORE_BY_PIECES,
 		 optimize_insn_for_speed_p ()));
 
-  store_by_pieces_d data (to, constfun, constfundata, len, align);
+  store_by_pieces_d data (to, constfun, constfundata, len, align,
+			  memsetp);
   data.run ();
 
   if (retmode != RETURN_BEGIN)
@@ -1513,15 +1584,6 @@ store_by_pieces (rtx to, unsigned HOST_WIDE_INT len,
     return to;
 }
 
-/* Callback routine for clear_by_pieces.
-   Return const0_rtx unconditionally.  */
-
-static rtx
-clear_by_pieces_1 (void *, void *, HOST_WIDE_INT, scalar_int_mode)
-{
-  return const0_rtx;
-}
-
 /* Generate several move instructions to clear LEN bytes of block TO.  (A MEM
    rtx with BLKmode).  ALIGN is maximum alignment we can assume.  */
 
@@ -1531,7 +1593,10 @@ clear_by_pieces (rtx to, unsigned HOST_WIDE_INT len, unsigned int align)
   if (len == 0)
     return;
 
-  store_by_pieces_d data (to, clear_by_pieces_1, NULL, len, align);
+  /* Use builtin_memset_read_str to support vector mode broadcast.  */
+  char c = 0;
+  store_by_pieces_d data (to, builtin_memset_read_str, &c, len, align,
+			  true);
   data.run ();
 }
 
@@ -5754,7 +5819,7 @@ emit_storent_insn (rtx to, rtx from)
 
 static rtx
 string_cst_read_str (void *data, void *, HOST_WIDE_INT offset,
-		     scalar_int_mode mode)
+		     fixed_size_mode mode)
 {
   tree str = (tree) data;
 
@@ -5769,10 +5834,13 @@ string_cst_read_str (void *data, void *, HOST_WIDE_INT offset,
       size_t l = TREE_STRING_LENGTH (str) - offset;
       memcpy (p, TREE_STRING_POINTER (str) + offset, l);
       memset (p + l, '\0', GET_MODE_SIZE (mode) - l);
-      return c_readstr (p, mode, false);
+      return c_readstr (p, as_a <scalar_int_mode> (mode), false);
     }
 
-  return c_readstr (TREE_STRING_POINTER (str) + offset, mode, false);
+  /* The by-pieces infrastructure does not try to pick a vector mode
+     for storing STRING_CST.  */
+  return c_readstr (TREE_STRING_POINTER (str) + offset,
+		    as_a <scalar_int_mode> (mode), false);
 }
 
 /* Generate code for computing expression EXP,
diff --git a/gcc/expr.h b/gcc/expr.h
index a4f44265759..94a85b40dca 100644
--- a/gcc/expr.h
+++ b/gcc/expr.h
@@ -108,13 +108,13 @@ enum block_op_methods
 };
 
 typedef rtx (*by_pieces_constfn) (void *, void *, HOST_WIDE_INT,
-				  scalar_int_mode);
+				  fixed_size_mode);
 
 /* The second pointer passed to by_pieces_constfn.  */
 struct by_pieces_prev
 {
   rtx data;
-  scalar_int_mode mode;
+  fixed_size_mode mode;
 };
 
 extern rtx emit_block_move (rtx, rtx, rtx, enum block_op_methods);
diff --git a/gcc/rtl.h b/gcc/rtl.h
index 5ffe90030fb..5fdcdfcd728 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -2460,6 +2460,8 @@ extern bool subreg_offset_representable_p (unsigned int, machine_mode,
 extern unsigned int subreg_regno (const_rtx);
 extern int simplify_subreg_regno (unsigned int, machine_mode,
 				  poly_uint64, machine_mode);
+extern int lowpart_subreg_regno (unsigned int, machine_mode,
+				 machine_mode);
 extern unsigned int subreg_nregs (const_rtx);
 extern unsigned int subreg_nregs_with_regno (unsigned int, const_rtx);
 extern unsigned HOST_WIDE_INT nonzero_bits (const_rtx, machine_mode);
diff --git a/gcc/rtlanal.c b/gcc/rtlanal.c
index ec7a062829c..3b8d88afd4d 100644
--- a/gcc/rtlanal.c
+++ b/gcc/rtlanal.c
@@ -4325,6 +4325,17 @@ simplify_subreg_regno (unsigned int xregno, machine_mode xmode,
   return (int) yregno;
 }
 
+/* A wrapper around simplify_subreg_regno that uses subreg_lowpart_offset
+   (xmode, ymode) as the offset.  */
+
+int
+lowpart_subreg_regno (unsigned int regno, machine_mode xmode,
+		      machine_mode ymode)
+{
+  poly_uint64 offset = subreg_lowpart_offset (xmode, ymode);
+  return simplify_subreg_regno (regno, xmode, offset, ymode);
+}
+
 /* Return the final regno that a subreg expression refers to.  */
 unsigned int
 subreg_regno (const_rtx x)
diff --git a/gcc/target.def b/gcc/target.def
index 6b4226c0651..68a46aaa832 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -2726,6 +2726,15 @@ DEFHOOK
  rtx, (rtx_insn **prep_seq, rtx_insn **gen_seq, rtx prev, int cmp_code, tree op0, tree op1, int bit_code),
  NULL)
 
+DEFHOOK
+(gen_memset_scratch_rtx,
+ "This hook should return an rtx for a scratch register in @var{mode} to\n\
+be used when expanding memset calls.  The backend can use a hard scratch\n\
+register to avoid stack realignment when expanding memset.  The default\n\
+is @code{gen_reg_rtx}.",
+ rtx, (machine_mode mode),
+ gen_reg_rtx)
+
 /* Return a new value for loop unroll size.  */
 DEFHOOK
 (loop_unroll_adjust,
diff --git a/gcc/testsuite/gcc.target/i386/pr100865-3.c b/gcc/testsuite/gcc.target/i386/pr100865-3.c
index b6dbcf7809b..007e79f91b0 100644
--- a/gcc/testsuite/gcc.target/i386/pr100865-3.c
+++ b/gcc/testsuite/gcc.target/i386/pr100865-3.c
@@ -10,6 +10,6 @@ foo (void)
 }
 
 /* { dg-final { scan-assembler-times "vpbroadcastb\[\\t \]+%(?:r|e)\[^\n\]*, %xmm\[0-9\]+" 1 } } */
-/* { dg-final { scan-assembler-times "vmovdqu\[\\t \]%xmm\[0-9\]+, \\(%\[\^,\]+\\)" 1 } } */
+/* { dg-final { scan-assembler-times "vmovdqu8\[\\t \]%xmm\[0-9\]+, \\(%\[\^,\]+\\)" 1 } } */
 /* { dg-final { scan-assembler-not "vpbroadcastb\[\\t \]+%xmm\[0-9\]+, %xmm\[0-9\]+" } } */
 /* { dg-final { scan-assembler-not "vmovdqa" } } */
diff --git a/gcc/testsuite/gcc.target/i386/pr100865-4b.c b/gcc/testsuite/gcc.target/i386/pr100865-4b.c
index f41e6147b4c..1e50dc842bc 100644
--- a/gcc/testsuite/gcc.target/i386/pr100865-4b.c
+++ b/gcc/testsuite/gcc.target/i386/pr100865-4b.c
@@ -4,6 +4,6 @@
 #include "pr100865-4a.c"
 
 /* { dg-final { scan-assembler-times "vpbroadcastb\[\\t \]+%(?:r|e)\[^\n\]*, %xmm\[0-9\]+" 1 } } */
-/* { dg-final { scan-assembler-times "vmovdqu\[\\t \]%xmm\[0-9\]+, " 4 } } */
+/* { dg-final { scan-assembler-times "vmovdqu8\[\\t \]%xmm\[0-9\]+, " 4 } } */
 /* { dg-final { scan-assembler-not "vpbroadcastb\[\\t \]+%xmm\[0-9\]+, %xmm\[0-9\]+" } } */
 /* { dg-final { scan-assembler-not "vmovdqa" } } */
