allow constructing a auto_vec with a preallocation, and a possibly larger actual allocation size

This allows us to set the capacity of the vector when we construct it,
and still use a stack buffer when the size is small enough.

gcc/ChangeLog:

2017-05-13  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	* genrecog.c (int_set::int_set): Explicitly construct our
	auto_vec base class.
	* vec.h (auto_vec::auto_vec): New constructor.

From-SVN: r248019

gcc/ChangeLog

 2017-05-13  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>
 
+	* genrecog.c (int_set::int_set): Explicitly construct our
+	auto_vec base class.
+	* vec.h (auto_vec::auto_vec): New constructor.
+
+2017-05-13  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>
+
 	* bitmap.h (class auto_bitmap): New constructor taking
 	bitmap_obstack * argument.
 

gcc/genrecog.c

@@ -1407,14 +1407,16 @@ struct int_set : public auto_vec <uint64_t, 1>
   iterator end ();
 };
 
-int_set::int_set () {}
+int_set::int_set () : auto_vec<uint64_t, 1> () {}
 
-int_set::int_set (uint64_t label)
+int_set::int_set (uint64_t label) :
+  auto_vec<uint64_t, 1> ()
 {
   safe_push (label);
 }
 
-int_set::int_set (const int_set &other)
+int_set::int_set (const int_set &other) :
+  auto_vec<uint64_t, 1> ()
 {
   safe_splice (other);
 }

gcc/vec.h

@@ -1272,6 +1272,18 @@ public:
     this->m_vec = &m_auto;
   }
 
+  auto_vec (size_t s)
+  {
+    if (s > N)
+      {
+	this->create (s);
+	return;
+      }
+
+    m_auto.embedded_init (MAX (N, 2), 0, 1);
+    this->m_vec = &m_auto;
+  }
+
   ~auto_vec ()
   {
     this->release ();