PR middle-end/90904 - vec assignment and copying undefined

gcc/ChangeLog:

	* vec.c (test_copy_assign): New function.
	(vec_c_tests): Call it.
	* vec.h (auto_vec copy ctor): Define.
	(auto_vec::operator=): Define.

diff --git a/gcc/vec.c b/gcc/vec.c
index f9dbb2cac31..c9299875257 100644
--- a/gcc/vec.c
+++ b/gcc/vec.c
@@ -317,6 +317,83 @@ test_safe_push ()
   ASSERT_EQ (7, v[2]);
 }
 
+/* Verify that auto_vec copy ctor and assignment work correctly.  */
+
+static void
+test_copy_assign ()
+{
+  auto_vec <int> a0;
+  auto_vec <int> b0 (0);
+  auto_vec <int> c0 (7);
+  ASSERT_EQ (0, b0.length ());
+  ASSERT_EQ (0, c0.length ());
+
+  a0 = a0;
+  ASSERT_EQ (0, a0.length ());
+  b0 = a0;
+  ASSERT_EQ (0, b0.length ());
+  c0 = a0;
+  ASSERT_EQ (0, c0.length ());
+
+  auto_vec <int> a3;
+  a3.safe_push (5);
+  a3.safe_push (6);
+  a3.safe_push (7);
+
+  auto_vec <int> b3 (a3);
+  ASSERT_EQ (3, b3.length ());
+  ASSERT_EQ (5, b3[0]);
+  ASSERT_EQ (6, b3[1]);
+  ASSERT_EQ (7, b3[2]);
+
+  auto_vec <int> c3;
+  c3 = b3;
+  ASSERT_EQ (3, c3.length ());
+  ASSERT_EQ (5, c3[0]);
+  ASSERT_EQ (6, c3[1]);
+  ASSERT_EQ (7, c3[2]);
+
+  auto_vec <int> d4;
+  d4.safe_push (1);
+  d4.safe_push (2);
+  d4.safe_push (3);
+  d4.safe_push (4);
+
+  c3 = d4;
+  ASSERT_EQ (4, c3.length ());
+  ASSERT_EQ (1, c3[0]);
+  ASSERT_EQ (2, c3[1]);
+  ASSERT_EQ (3, c3[2]);
+  ASSERT_EQ (4, c3[3]);
+
+  d4 = a3;
+  ASSERT_EQ (3, d4.length ());
+  ASSERT_EQ (5, d4[0]);
+  ASSERT_EQ (6, d4[1]);
+  ASSERT_EQ (7, d4[2]);
+
+  a3 = b0;
+  ASSERT_EQ (0, a3.length ());
+
+  b3 = b0;
+  ASSERT_EQ (0, b3.length ());
+
+  c3 = c0;
+  ASSERT_EQ (0, c3.length ());
+
+  b0 = d4;
+  ASSERT_EQ (3, b0.length ());
+  ASSERT_EQ (5, b0[0]);
+  ASSERT_EQ (6, b0[1]);
+  ASSERT_EQ (7, b0[2]);
+
+  c0 = d4;
+  ASSERT_EQ (3, c0.length ());
+  ASSERT_EQ (5, c0[0]);
+  ASSERT_EQ (6, c0[1]);
+  ASSERT_EQ (7, c0[2]);
+}
+
 /* Verify that vec::truncate works correctly.  */
 
 static void
@@ -549,6 +626,7 @@ vec_c_tests ()
 {
   test_quick_push ();
   test_safe_push ();
+  test_copy_assign ();
   test_truncate ();
   test_safe_grow_cleared ();
   test_pop ();
diff --git a/gcc/vec.h b/gcc/vec.h
index 24df2db0eeb..61397bb7ee0 100644
--- a/gcc/vec.h
+++ b/gcc/vec.h
@@ -1551,12 +1551,21 @@ public:
   auto_vec (size_t n CXX_MEM_STAT_INFO) { this->create (n PASS_MEM_STAT); }
   ~auto_vec () { this->release (); }
 
+  /* Copy ctor.  */
+  auto_vec (const auto_vec&);
+
+  /* Move ctor from a heap-allocated vec.  */
   auto_vec (vec<T, va_heap>&& r)
     {
       gcc_assert (!r.using_auto_storage ());
       this->m_vec = r.m_vec;
       r.m_vec = NULL;
     }
+
+  /* Copy asssignment.  */
+  auto_vec& operator= (const auto_vec&);
+
+  /* Move asssignment from a heap-allocated vec.  */
   auto_vec& operator= (vec<T, va_heap>&& r)
     {
       gcc_assert (!r.using_auto_storage ());
@@ -1567,6 +1576,49 @@ public:
     }
 };
 
+/* Copy elements from R to *THIS.  */
+
+template<typename T>
+auto_vec<T, 0>::auto_vec (const auto_vec& r)
+{
+  const unsigned n = r.length ();
+  this->create (n);
+  if (n)
+    {
+      vec_copy_construct (this->address (), r.address (), n);
+      this->m_vec->m_vecpfx.m_num = n;
+    }
+}
+
+/* Assign elements from R over *THIS, invoking the copy assignment
+   operator on the initial elements and the copy ctor on the excess.  */
+
+template<typename T>
+auto_vec<T, 0>& auto_vec<T, 0>::operator= (const auto_vec& r)
+{
+  unsigned n0 = this->length ();
+  const unsigned n1 = r.length ();
+  if (n0 < n1)
+    this->safe_grow (n1);
+  else
+    {
+      this->truncate (n1);
+      n0 = n1;
+    }
+
+  T *dst = this->address ();
+  const T *src = r.address ();
+
+  /* Copy-assign over the first N0 elements.  */
+  for (unsigned i = 0; i != n0; ++i)
+    dst[i] = src[i];
+
+  if (n0 < n1)
+    /* Copy-construct elements in excess of N0.  */
+    vec_copy_construct (dst + n0, src + n0, n1 - n0);
+
+  return *this;
+}
 
 /* Allocate heap memory for pointer V and create the internal vector
    with space for NELEMS elements.  If NELEMS is 0, the internal