diff --git a/gcc/config/riscv/riscv-protos.h b/gcc/config/riscv/riscv-protos.h
index eaee53ce94e..c4531589300 100644
--- a/gcc/config/riscv/riscv-protos.h
+++ b/gcc/config/riscv/riscv-protos.h
@@ -637,6 +637,7 @@ void expand_popcount (rtx *);
 void expand_rawmemchr (machine_mode, rtx, rtx, rtx, bool = false);
 bool expand_strcmp (rtx, rtx, rtx, rtx, unsigned HOST_WIDE_INT, bool);
 void emit_vec_extract (rtx, rtx, rtx);
+bool expand_vec_setmem (rtx, rtx, rtx, rtx);
 
 /* Rounding mode bitfield for fixed point VXRM.  */
 enum fixed_point_rounding_mode
diff --git a/gcc/config/riscv/riscv-string.cc b/gcc/config/riscv/riscv-string.cc
index 11c1f74d0b3..e506b92a552 100644
--- a/gcc/config/riscv/riscv-string.cc
+++ b/gcc/config/riscv/riscv-string.cc
@@ -1247,4 +1247,94 @@ expand_strcmp (rtx result, rtx src1, rtx src2, rtx nbytes,
   return true;
 }
 
+/* Check we are permitted to vectorise a memory operation.
+   If so, return true and populate lmul_out.
+   Otherwise, return false and leave lmul_out unchanged.  */
+static bool
+check_vectorise_memory_operation (rtx length_in, HOST_WIDE_INT &lmul_out)
+{
+  /* If we either can't or have been asked not to vectorise, respect this.  */
+  if (!TARGET_VECTOR)
+    return false;
+  if (!(stringop_strategy & STRATEGY_VECTOR))
+    return false;
+
+  /* If we can't reason about the length, don't vectorise.  */
+  if (!CONST_INT_P (length_in))
+    return false;
+
+  HOST_WIDE_INT length = INTVAL (length_in);
+
+  /* If it's tiny, default operation is likely better; maybe worth
+     considering fractional lmul in the future as well.  */
+  if (length < (TARGET_MIN_VLEN / 8))
+    return false;
+
+  /* If we've been asked to use a specific LMUL,
+     check the operation fits and do that.  */
+  if (riscv_autovec_lmul != RVV_DYNAMIC)
+    {
+      lmul_out = TARGET_MAX_LMUL;
+      return (length <= ((TARGET_MAX_LMUL * TARGET_MIN_VLEN) / 8));
+    }
+
+  /* Find smallest lmul large enough for entire op.  */
+  HOST_WIDE_INT lmul = 1;
+  while ((lmul <= 8) && (length > ((lmul * TARGET_MIN_VLEN) / 8)))
+    {
+      lmul <<= 1;
+    }
+
+  if (lmul > 8)
+    return false;
+
+  lmul_out = lmul;
+  return true;
+}
+
+/* Used by setmemdi in riscv.md.  */
+bool
+expand_vec_setmem (rtx dst_in, rtx length_in, rtx fill_value_in,
+		   rtx alignment_in)
+{
+  HOST_WIDE_INT lmul;
+  /* Check we are able and allowed to vectorise this operation;
+     bail if not.  */
+  if (!check_vectorise_memory_operation (length_in, lmul))
+    return false;
+
+  machine_mode vmode
+      = riscv_vector::get_vector_mode (QImode, BYTES_PER_RISCV_VECTOR * lmul)
+	    .require ();
+  rtx dst_addr = copy_addr_to_reg (XEXP (dst_in, 0));
+  rtx dst = change_address (dst_in, vmode, dst_addr);
+
+  rtx fill_value = gen_reg_rtx (vmode);
+  rtx broadcast_ops[] = { fill_value, fill_value_in };
+
+  /* If the length is exactly vlmax for the selected mode, do that.
+     Otherwise, use a predicated store.  */
+  if (known_eq (GET_MODE_SIZE (vmode), INTVAL (length_in)))
+    {
+      emit_vlmax_insn (code_for_pred_broadcast (vmode), UNARY_OP,
+			  broadcast_ops);
+      emit_move_insn (dst, fill_value);
+    }
+  else
+    {
+      if (!satisfies_constraint_K (length_in))
+	      length_in = force_reg (Pmode, length_in);
+      emit_nonvlmax_insn (code_for_pred_broadcast (vmode), UNARY_OP,
+			  broadcast_ops, length_in);
+      machine_mode mask_mode
+	      = riscv_vector::get_vector_mode (BImode, GET_MODE_NUNITS (vmode))
+		      .require ();
+      rtx mask = CONSTM1_RTX (mask_mode);
+      emit_insn (gen_pred_store (vmode, dst, mask, fill_value, length_in,
+			  get_avl_type_rtx (riscv_vector::NONVLMAX)));
+    }
+
+  return true;
+}
+
 }
diff --git a/gcc/config/riscv/riscv.md b/gcc/config/riscv/riscv.md
index 1b3f66fd15c..dd34211ca80 100644
--- a/gcc/config/riscv/riscv.md
+++ b/gcc/config/riscv/riscv.md
@@ -2387,6 +2387,20 @@
     FAIL;
 })
 
+(define_expand "setmemsi"
+  [(set (match_operand:BLK 0 "memory_operand")     ;; Dest
+	      (match_operand:QI  2 "nonmemory_operand")) ;; Value
+   (use (match_operand:SI  1 "const_int_operand")) ;; Length
+   (match_operand:SI       3 "const_int_operand")] ;; Align
+  "TARGET_VECTOR"
+{
+  if (riscv_vector::expand_vec_setmem (operands[0], operands[1], operands[2],
+      operands[3]))
+    DONE;
+  else
+    FAIL;
+})
+
 ;; Expand in-line code to clear the instruction cache between operand[0] and
 ;; operand[1].
 (define_expand "clear_cache"
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/base/setmem-1.c b/gcc/testsuite/gcc.target/riscv/rvv/base/setmem-1.c
new file mode 100644
index 00000000000..1c08be978a6
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/base/setmem-1.c
@@ -0,0 +1,103 @@
+/* { dg-do compile } */
+/* { dg-add-options riscv_v } */
+/* { dg-additional-options "-O3 --param=riscv-autovec-lmul=dynamic" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+#define MIN_VECTOR_BYTES (__riscv_v_min_vlen / 8)
+
+/* Tiny memsets should use scalar ops.
+** f1:
+**  sb\s+a1,0\(a0\)
+**  ret
+*/
+void *
+f1 (void *a, int const b)
+{
+  return __builtin_memset (a, b, 1);
+}
+
+/* Tiny memsets should use scalar ops.
+** f2:
+**  sb\s+a1,0\(a0\)
+**  sb\s+a1,1\(a0\)
+**  ret
+*/
+void *
+f2 (void *a, int const b)
+{
+  return __builtin_memset (a, b, 2);
+}
+
+/* Tiny memsets should use scalar ops.
+** f3:
+**  sb\s+a1,0\(a0\)
+**  sb\s+a1,1\(a0\)
+**  sb\s+a1,2\(a0\)
+**  ret
+*/
+void *
+f3 (void *a, int const b)
+{
+  return __builtin_memset (a, b, 3);
+}
+
+/* Vectorise+inline minimum vector register width with LMUL=1
+** f4:
+**  (
+**  vsetivli\s+zero,\d+,e8,m1,ta,ma
+**  |
+**  li\s+a\d+,\d+
+**  vsetvli\s+zero,a\d+,e8,m1,ta,ma
+**  )
+**  vmv\.v\.x\s+v\d+,a1
+**  vse8\.v\s+v\d+,0\(a0\)
+**  ret
+*/
+void *
+f4 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES);
+}
+
+/* Vectorised code should use smallest lmul known to fit length
+** f5:
+**  (
+**  vsetivli\s+zero,\d+,e8,m2,ta,ma
+**  |
+**  li\s+a\d+,\d+
+**  vsetvli\s+zero,a\d+,e8,m2,ta,ma
+**  )
+**  vmv\.v\.x\s+v\d+,a1
+**  vse8\.v\s+v\d+,0\(a0\)
+**  ret
+*/
+void *
+f5 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES + 1);
+}
+
+/* Vectorise+inline up to LMUL=8
+** f6:
+**  li\s+a\d+,\d+
+**  vsetvli\s+zero,a\d+,e8,m8,ta,ma
+**  vmv\.v\.x\s+v\d+,a1
+**  vse8\.v\s+v\d+,0\(a0\)
+**  ret
+*/
+void *
+f6 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES * 8);
+}
+
+/* Don't vectorise if the move is too large for one operation.
+** f7:
+**  li\s+a2,\d+
+**  tail\s+memset
+*/
+void *
+f7 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES * 8 + 1);
+}
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/base/setmem-2.c b/gcc/testsuite/gcc.target/riscv/rvv/base/setmem-2.c
new file mode 100644
index 00000000000..82d181dff3f
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/base/setmem-2.c
@@ -0,0 +1,51 @@
+/* { dg-do compile } */
+/* { dg-add-options riscv_v } */
+/* { dg-additional-options "-O3 --param riscv-autovec-lmul=m1" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+#define MIN_VECTOR_BYTES (__riscv_v_min_vlen / 8)
+
+/* Small memsets shouldn't be vectorised.
+** f1:
+**  (
+**  sb\s+a1,0\(a0\)
+**  ...
+**  |
+**  li\s+a2,\d+
+**  tail\s+memset
+**  )
+*/
+void *
+f1 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES - 1);
+}
+
+/* Vectorise+inline minimum vector register width using requested lmul.
+** f2:
+**  (
+**  vsetivli\s+zero,\d+,e8,m1,ta,ma
+**  |
+**  li\s+a\d+,\d+
+**  vsetvli\s+zero,a\d+,e8,m1,ta,ma
+**  )
+**  vmv\.v\.x\s+v\d+,a1
+**  vse8\.v\s+v\d+,0\(a0\)
+**  ret
+*/
+void *
+f2 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES);
+}
+
+/* Don't vectorise if the move is too large for requested lmul.
+** f3:
+**  li\s+a2,\d+
+**  tail\s+memset
+*/
+void *
+f3 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES + 1);
+}
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/base/setmem-3.c b/gcc/testsuite/gcc.target/riscv/rvv/base/setmem-3.c
new file mode 100644
index 00000000000..f043d9e0784
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/base/setmem-3.c
@@ -0,0 +1,69 @@
+/* { dg-do compile } */
+/* { dg-add-options riscv_v } */
+/* { dg-additional-options "-O3 --param riscv-autovec-lmul=m8" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+#define MIN_VECTOR_BYTES (__riscv_v_min_vlen / 8)
+
+/* Small memsets shouldn't be vectorised.
+** f1:
+**  (
+**  sb\s+a1,0\(a0\)
+**  ...
+**  |
+**  li\s+a2,\d+
+**  tail\s+memset
+**  )
+*/
+void *
+f1 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES - 1);
+}
+
+/* Vectorise+inline minimum vector register width using requested lmul.
+** f2:
+**  (
+**  vsetivli\s+zero,\d+,e8,m8,ta,ma
+**  |
+**  li\s+a\d+,\d+
+**  vsetvli\s+zero,a\d+,e8,m8,ta,ma
+**  )
+**  vmv\.v\.x\s+v\d+,a1
+**  vse8\.v\s+v\d+,0\(a0\)
+**  ret
+*/
+void *
+f2 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES);
+}
+
+/* Vectorise+inline operations up to requested lmul.
+** f3:
+**  (
+**  vsetivli\s+zero,\d+,e8,m8,ta,ma
+**  |
+**  li\s+a\d+,\d+
+**  vsetvli\s+zero,a\d+,e8,m8,ta,ma
+**  )
+**  vmv\.v\.x\s+v\d+,a1
+**  vse8\.v\s+v\d+,0\(a0\)
+**  ret
+*/
+void *
+f3 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES * 8);
+}
+
+/* Don't vectorise if the move is too large for requested lmul.
+** f4:
+**  li\s+a2,\d+
+**  tail\s+memset
+*/
+void *
+f4 (void *a, int const b)
+{
+  return __builtin_memset (a, b, MIN_VECTOR_BYTES * 8 + 1);
+}
