diff --git a/gcc/config/riscv/riscv-v.cc b/gcc/config/riscv/riscv-v.cc
index 9b6c3a21e2d..a31766f3662 100644
--- a/gcc/config/riscv/riscv-v.cc
+++ b/gcc/config/riscv/riscv-v.cc
@@ -1104,7 +1104,7 @@ expand_vec_series (rtx dest, rtx base, rtx step, rtx vid)
     emit_move_insn (dest, result);
 }

-/* Subroutine of riscv_vector_expand_vector_init.
+/* Subroutine of riscv_vector_expand_vector_init and expand_const_vector.
    Works as follows:
    (a) Initialize TARGET by broadcasting element NELTS_REQD - 1 of BUILDER.
    (b) Skip leading elements from BUILDER, which are the same as
@@ -1129,7 +1129,7 @@ expand_vector_init_insert_elems (rtx target, const rvv_builder &builder,
     }
 }

-/* Subroutine of expand_vec_init to handle case
+/* Subroutine of expand_vec_init and expand_const_vector to handle case
    when all trailing elements of builder are same.
    This works as follows:
    (a) Use expand_insn interface to broadcast last vector element in TARGET.
@@ -1248,6 +1248,8 @@ expand_const_vector (rtx target, rtx src)
     }
   builder.finalize ();

+  bool emit_catch_all_pattern = false;
+
   if (CONST_VECTOR_DUPLICATE_P (src))
     {
       /* Handle the case with repeating sequence that NELTS_PER_PATTERN = 1
@@ -1555,10 +1557,24 @@ expand_const_vector (rtx target, rtx src)
 	}
       else
 	/* TODO: We will enable more variable-length vector in the future.  */
-	gcc_unreachable ();
+	emit_catch_all_pattern = true;
     }
   else
-    gcc_unreachable ();
+    emit_catch_all_pattern = true;
+
+  if (emit_catch_all_pattern)
+    {
+      int nelts = XVECLEN (src, 0);
+
+      /* Optimize trailing same elements sequence:
+      v = {y, y2, y3, y4, y5, x, x, x, x, x, x, x, x, x, x, x};  */
+      if (!expand_vector_init_trailing_same_elem (result, builder, nelts))
+	/* Handle common situation with vslide1down.  This function can handle
+	   any case of vec_init<mode>.  Only the cases that are not optimized
+	   above will fall through here.  This prevents us from dumping
+	   to/reading from the stack to initialize vectors.  */
+	expand_vector_init_insert_elems (result, builder, nelts);
+    }

   if (result != target)
     emit_move_insn (target, result);
diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
index 400b1059666..ac7fdbf71af 100644
--- a/gcc/config/riscv/riscv.cc
+++ b/gcc/config/riscv/riscv.cc
@@ -2141,12 +2141,13 @@ riscv_const_insns (rtx x, bool allow_new_pseudos)
 	       out range of [-16, 15].
 	  - 3. const series vector.
 	  ...etc.  */
-	if (riscv_v_ext_mode_p (GET_MODE (x)))
+	machine_mode mode = GET_MODE (x);
+	if (riscv_v_ext_mode_p (mode))
 	  {
 	    rtx elt;
 	    if (const_vec_duplicate_p (x, &elt))
 	      {
-		if (GET_MODE_CLASS (GET_MODE (x)) == MODE_VECTOR_BOOL)
+		if (GET_MODE_CLASS (mode) == MODE_VECTOR_BOOL)
 		  /* Duplicate values of 0/1 can be emitted using vmv.v.i.  */
 		  return 1;

@@ -2154,7 +2155,7 @@ riscv_const_insns (rtx x, bool allow_new_pseudos)
 		   system since the ELT constant value can not held
 		   within a single register to disable reload a DI
 		   register vec_duplicate into vmv.v.x.  */
-		scalar_mode smode = GET_MODE_INNER (GET_MODE (x));
+		scalar_mode smode = GET_MODE_INNER (mode);
 		if (maybe_gt (GET_MODE_SIZE (smode), UNITS_PER_WORD)
 		    && !immediate_operand (elt, Pmode))
 		  return 0;
@@ -2190,14 +2191,22 @@ riscv_const_insns (rtx x, bool allow_new_pseudos)
 		return 1;
 	      }

-	    if (CONST_VECTOR_STEPPED_P (x))
+	    if (CONST_VECTOR_DUPLICATE_P (x))
+	      {
+		/* TODO: Cost cases of CONST_VECTOR_DUPLICATE_P.
+		   We get ICEs with could not split insn from an
+		   expand_vector_broadcast emitted during LRA when this op is
+		   costed.  For now disallow all cases.  */
+		return 0;
+	      }
+	    else if (CONST_VECTOR_STEPPED_P (x))
 	      {
 		/* Some cases are unhandled so we need construct a builder to
 		   detect/allow those cases to be handled by the fallthrough
 		   handler.  */
 		unsigned int nelts_per_pattern = CONST_VECTOR_NELTS_PER_PATTERN (x);
 		unsigned int npatterns = CONST_VECTOR_NPATTERNS (x);
-		rvv_builder builder (GET_MODE(x), npatterns, nelts_per_pattern);
+		rvv_builder builder (mode, npatterns, nelts_per_pattern);
 		for (unsigned int i = 0; i < nelts_per_pattern; i++)
 		  {
 		    for (unsigned int j = 0; j < npatterns; j++)
@@ -2224,12 +2233,97 @@ riscv_const_insns (rtx x, bool allow_new_pseudos)
 		    return 1;
 		  }

-		/* Fallthrough.  */
+		/* Fallthrough to catch all pattern.  */
+	      }
+
+	    int nelts = const_vector_encoded_nelts (x);
+	    if (nelts == 0)
+	      return 0;
+
+	    /* Most arbitrary vectors can be constructed with a splat and
+	       vslide1up/down.  */
+
+	    /* The arbitrary vector's elements must be supported by the
+	       vslide1up/down operation.  */
+	    scalar_mode smode = GET_MODE_INNER (mode);
+	    if (maybe_gt (GET_MODE_SIZE (smode), UNITS_PER_WORD))
+	      /* vslide1up/down does not handle elts larger than a register.  */
+	      return 0;
+	    if (GET_MODE_CLASS (mode) == MODE_VECTOR_BOOL)
+	      /* vslide1up/down does not handle BImode elts.  */
+	      return 0;
+	    if (GET_MODE_CLASS (mode) == MODE_VECTOR_FLOAT
+		&& maybe_lt (GET_MODE_SIZE (smode), 4))
+	      /* Our vslide1up/down insn def does not handle HF.  */
+	      return 0;
+
+	    /* We already checked for a fully const vector above.  Calculate
+	       the number of leading/trailing elements covered by the splat.  */
+	    int leading_ndups = 1;
+	    rtx first_elt = CONST_VECTOR_ENCODED_ELT (x, 0);
+	    for (int i = 1; i < nelts; i++)
+	      {
+		if (first_elt == CONST_VECTOR_ENCODED_ELT (x, i))
+		  leading_ndups += 1;
+		else
+		  break;
+	      }
+	    int trailing_ndups = 1;
+	    if (leading_ndups >= nelts / 2)
+	      /* We already know leading_ndups >= trailing_ndups so just use
+		 leading ndups.  */
+	      trailing_ndups = 0;
+	    else
+	      {
+		rtx last_elt = CONST_VECTOR_ENCODED_ELT (x, nelts - 1);
+		for (int i = nelts - 2; i > 0; i--)
+		  {
+		    if (last_elt == CONST_VECTOR_ENCODED_ELT (x, i))
+		      trailing_ndups += 1;
+		    else
+		      break;
+		  }
 	      }
+
+	    /* We always splat the leading/trailing elt with the most contigious
+	       duplicates.  */
+	    int splatted_leading = 0;
+	    int splatted_trailing = 0;
+	    int splat_materialize = 0;
+	    if (leading_ndups > trailing_ndups)
+	      {
+		splatted_leading = leading_ndups;
+		splat_materialize = riscv_const_insns (CONST_VECTOR_ELT (x, 0),
+						       allow_new_pseudos);
+	      }
+	    else
+	      {
+		splatted_trailing = trailing_ndups;
+		splat_materialize =
+		  riscv_const_insns (CONST_VECTOR_ELT (x, nelts - 1),
+				     allow_new_pseudos);
+	      }
+
+	    /* Splat leading/trailing elt.  */
+	    int total_insns = splat_materialize + 1;
+
+	    /* TODO: There's room for improvement here.  eg.  duplicate
+	       constants won't require another materialization.  */
+	    for (int i = splatted_leading; i < nelts - splatted_trailing; i++)
+	      {
+		rtx elt = CONST_VECTOR_ELT (x, i);
+		int n = riscv_const_insns (elt, allow_new_pseudos);
+		if (n == 0)
+		  n = 4; /* memory access.  */
+		/* materialize + vslide1{up|down}.  */
+		total_insns += n + 1;
+	      }
+
+	    return total_insns;
 	  }

 	/* TODO: We may support more const vector in the future.  */
-	return x == CONST0_RTX (GET_MODE (x)) ? 1 : 0;
+	return x == CONST0_RTX (mode) ? 1 : 0;
       }

     case CONST:
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-1.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-1.c
new file mode 100644
index 00000000000..2d7e1cf1556
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-1.c
@@ -0,0 +1,13 @@
+/* Vector constants can be constructed using splat + vslide1up.  */
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv_zvl128b -mabi=lp64d -O3" } */
+
+void slide1up(int a, int *b) {
+  int c[4] = {1, 10, 10, 10};
+  for (int j = 0; j < 4; j++) {
+    b[j] = c[j];
+  }
+}
+
+/* { dg-final { scan-assembler-times {vmv.v.i} 1 } } */
+/* { dg-final { scan-assembler-times {vslide1up.vx} 1 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-2.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-2.c
new file mode 100644
index 00000000000..22d8365814c
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-2.c
@@ -0,0 +1,13 @@
+/* Vector constants can be constructed using splat + vslide1up.  */
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv_zvl256b -mabi=lp64d -O3" } */
+
+void slide1up(int a, int *b) {
+  int c[8] = {1, 1, 1, 10, 10, 10, 10, 10};
+  for (int j = 0; j < 8; j++) {
+    b[j] = c[j];
+  }
+}
+
+/* { dg-final { scan-assembler-times {vmv.v.i} 1 } } */
+/* { dg-final { scan-assembler-times {vslide1up.vx} 3 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-3.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-3.c
new file mode 100644
index 00000000000..928e3d5fc74
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-3.c
@@ -0,0 +1,13 @@
+/* Vector constants can be constructed using splat + vslide1down.  */
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv_zvl128b -mabi=lp64d -O3" } */
+
+void slide1up(int a, int *b) {
+  int c[4] = {1, 1, 1, 10};
+  for (int j = 0; j < 4; j++) {
+    b[j] = c[j];
+  }
+}
+
+/* { dg-final { scan-assembler-times {vmv.v.i} 1 } } */
+/* { dg-final { scan-assembler-times {vslide1down.vx} 1 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-4.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-4.c
new file mode 100644
index 00000000000..ba1b880e901
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-4.c
@@ -0,0 +1,13 @@
+/* Vector constants can be constructed using splat + vslide1down.  */
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv_zvl256b -mabi=lp64d -O3" } */
+
+void slide1up(int a, int *b) {
+  int c[8] = {1, 1, 1, 1, 1, 10, 10, 10};
+  for (int j = 0; j < 8; j++) {
+    b[j] = c[j];
+  }
+}
+
+/* { dg-final { scan-assembler-times {vmv.v.i} 1 } } */
+/* { dg-final { scan-assembler-times {vslide1down.vx} 3 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-5.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-5.c
new file mode 100644
index 00000000000..6fd68ec4a55
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-5.c
@@ -0,0 +1,13 @@
+/* Arbitrary vector constants can be constructed using splat + vslide1{up|down}.  */
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv_zvl128b -mabi=lp64d -O3" } */
+
+void slide1down_arbitrary(int a, int *b) {
+  int c[4] = {100, 12, 324, 1};
+  for (int j = 0; j < 4; j++) {
+    b[j] = c[j];
+  }
+}
+
+/* { dg-final { scan-assembler-times {vmv.v.x} 1 } } */
+/* { dg-final { scan-assembler-times {vslide1(up|down).vx} 3 } } */
diff --git a/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-6.c b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-6.c
new file mode 100644
index 00000000000..0de98bf26b9
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/rvv/autovec/materialize-6.c
@@ -0,0 +1,13 @@
+/* Arbitrary vector constants can be constructed using splat + vslide1{up|down}.  */
+/* { dg-do compile } */
+/* { dg-options "-march=rv64gcv_zvl256b -mabi=lp64d -O3" } */
+
+void slide1down_arbitrary(int a, int *b) {
+  int c[8] = {100, 12, 324, 1, 57, 16, 98, 60};
+  for (int j = 0; j < 8; j++) {
+    b[j] = c[j];
+  }
+}
+
+/* { dg-final { scan-assembler-times {vmv.v.x} 1 } } */
+/* { dg-final { scan-assembler-times {vslide1(up|down).vx} 7 } } */
