Index: gcc/expr.c
===================================================================
--- gcc/expr.c	2017-12-22 12:58:44.518127920 +0000
+++ gcc/expr.c	2017-12-22 13:09:48.535709302 +0000
@@ -61,6 +61,7 @@ Software Foundation; either version 3, o
 #include "tree-chkp.h"
 #include "rtl-chkp.h"
 #include "ccmp.h"
+#include "rtx-vector-builder.h"
 
 
 /* If this is nonzero, we do not bother generating VOLATILE
@@ -11761,32 +11762,25 @@ try_tablejump (tree index_type, tree ind
 static rtx
 const_vector_mask_from_tree (tree exp)
 {
-  rtvec v;
-  unsigned i, units;
-  tree elt;
-  machine_mode inner, mode;
-
-  mode = TYPE_MODE (TREE_TYPE (exp));
-  units = VECTOR_CST_NELTS (exp);
-  inner = GET_MODE_INNER (mode);
-
-  v = rtvec_alloc (units);
+  machine_mode mode = TYPE_MODE (TREE_TYPE (exp));
+  machine_mode inner = GET_MODE_INNER (mode);
 
-  for (i = 0; i < units; ++i)
+  rtx_vector_builder builder (mode, VECTOR_CST_NPATTERNS (exp),
+			      VECTOR_CST_NELTS_PER_PATTERN (exp));
+  unsigned int count = builder.encoded_nelts ();
+  for (unsigned int i = 0; i < count; ++i)
     {
-      elt = VECTOR_CST_ELT (exp, i);
-
+      tree elt = VECTOR_CST_ELT (exp, i);
       gcc_assert (TREE_CODE (elt) == INTEGER_CST);
       if (integer_zerop (elt))
-	RTVEC_ELT (v, i) = CONST0_RTX (inner);
+	builder.quick_push (CONST0_RTX (inner));
       else if (integer_onep (elt)
 	       || integer_minus_onep (elt))
-	RTVEC_ELT (v, i) = CONSTM1_RTX (inner);
+	builder.quick_push (CONSTM1_RTX (inner));
       else
 	gcc_unreachable ();
     }
-
-  return gen_rtx_CONST_VECTOR (mode, v);
+  return builder.build ();
 }
 
 /* EXP is a VECTOR_CST in which each element is either all-zeros or all-ones.
@@ -11816,12 +11810,7 @@ const_scalar_mask_from_tree (scalar_int_
 static rtx
 const_vector_from_tree (tree exp)
 {
-  rtvec v;
-  unsigned i, units;
-  tree elt;
-  machine_mode inner, mode;
-
-  mode = TYPE_MODE (TREE_TYPE (exp));
+  machine_mode mode = TYPE_MODE (TREE_TYPE (exp));
 
   if (initializer_zerop (exp))
     return CONST0_RTX (mode);
@@ -11829,27 +11818,25 @@ const_vector_from_tree (tree exp)
   if (VECTOR_BOOLEAN_TYPE_P (TREE_TYPE (exp)))
     return const_vector_mask_from_tree (exp);
 
-  units = VECTOR_CST_NELTS (exp);
-  inner = GET_MODE_INNER (mode);
-
-  v = rtvec_alloc (units);
+  machine_mode inner = GET_MODE_INNER (mode);
 
-  for (i = 0; i < units; ++i)
+  rtx_vector_builder builder (mode, VECTOR_CST_NPATTERNS (exp),
+			      VECTOR_CST_NELTS_PER_PATTERN (exp));
+  unsigned int count = builder.encoded_nelts ();
+  for (unsigned int i = 0; i < count; ++i)
     {
-      elt = VECTOR_CST_ELT (exp, i);
-
+      tree elt = VECTOR_CST_ELT (exp, i);
       if (TREE_CODE (elt) == REAL_CST)
-	RTVEC_ELT (v, i) = const_double_from_real_value (TREE_REAL_CST (elt),
-							 inner);
+	builder.quick_push (const_double_from_real_value (TREE_REAL_CST (elt),
+							  inner));
       else if (TREE_CODE (elt) == FIXED_CST)
-	RTVEC_ELT (v, i) = CONST_FIXED_FROM_FIXED_VALUE (TREE_FIXED_CST (elt),
-							 inner);
+	builder.quick_push (CONST_FIXED_FROM_FIXED_VALUE (TREE_FIXED_CST (elt),
+							  inner));
       else
-	RTVEC_ELT (v, i) = immed_wide_int_const (wi::to_poly_wide (elt),
-						 inner);
+	builder.quick_push (immed_wide_int_const (wi::to_poly_wide (elt),
+						  inner));
     }
-
-  return gen_rtx_CONST_VECTOR (mode, v);
+  return builder.build ();
 }
 
 /* Build a decl for a personality function given a language prefix.  */
Index: gcc/optabs.c
===================================================================
--- gcc/optabs.c	2017-12-22 13:06:03.092620276 +0000
+++ gcc/optabs.c	2017-12-22 13:09:48.535709302 +0000
@@ -33,6 +33,7 @@ Software Foundation; either version 3, o
 #include "emit-rtl.h"
 #include "recog.h"
 #include "diagnostic-core.h"
+#include "rtx-vector-builder.h"
 
 /* Include insn-config.h before expr.h so that HAVE_conditional_move
    is properly defined.  */
@@ -5609,7 +5610,6 @@ expand_vec_perm_var (machine_mode mode,
   enum insn_code icode;
   unsigned int i, w, u;
   rtx tmp, sel_qi;
-  rtvec vec;
 
   w = GET_MODE_SIZE (mode);
   u = GET_MODE_UNIT_SIZE (mode);
@@ -5661,10 +5661,10 @@ expand_vec_perm_var (machine_mode mode,
   /* Add the byte offset to each byte element.  */
   /* Note that the definition of the indicies here is memory ordering,
      so there should be no difference between big and little endian.  */
-  vec = rtvec_alloc (w);
-  for (i = 0; i < w; ++i)
-    RTVEC_ELT (vec, i) = GEN_INT (i % u);
-  tmp = gen_rtx_CONST_VECTOR (qimode, vec);
+  rtx_vector_builder byte_indices (qimode, u, 1);
+  for (i = 0; i < u; ++i)
+    byte_indices.quick_push (GEN_INT (i));
+  tmp = byte_indices.build ();
   sel_qi = expand_simple_binop (qimode, PLUS, sel, tmp,
 				sel, 0, OPTAB_DIRECT);
   gcc_assert (sel_qi != NULL);
Index: gcc/vec-perm-indices.c
===================================================================
--- gcc/vec-perm-indices.c	2017-12-22 13:05:20.155253154 +0000
+++ gcc/vec-perm-indices.c	2017-12-22 13:09:48.535709302 +0000
@@ -29,6 +29,7 @@ Software Foundation; either version 3, o
 #include "memmodel.h"
 #include "emit-rtl.h"
 #include "selftest.h"
+#include "rtx-vector-builder.h"
 
 /* Switch to a new permutation vector that selects between NINPUTS vector
    inputs that have NELTS_PER_INPUT elements each.  Take the elements of the
@@ -223,11 +224,12 @@ vec_perm_indices_to_rtx (machine_mode mo
 {
   gcc_assert (GET_MODE_CLASS (mode) == MODE_VECTOR_INT
 	      && GET_MODE_NUNITS (mode) == indices.length ());
-  unsigned int nelts = indices.length ();
-  rtvec v = rtvec_alloc (nelts);
-  for (unsigned int i = 0; i < nelts; ++i)
-    RTVEC_ELT (v, i) = gen_int_mode (indices[i], GET_MODE_INNER (mode));
-  return gen_rtx_CONST_VECTOR (mode, v);
+  rtx_vector_builder sel (mode, indices.encoding ().npatterns (),
+			  indices.encoding ().nelts_per_pattern ());
+  unsigned int encoded_nelts = sel.encoded_nelts ();
+  for (unsigned int i = 0; i < encoded_nelts; i++)
+    sel.quick_push (gen_int_mode (indices[i], GET_MODE_INNER (mode)));
+  return sel.build ();
 }
 
 #if CHECKING_P
