[PATCH] Fix ctor reference folding (PR middle-end/65554)

[Marek Polacek]

This test was failing at -O due to non-trivial conversion at assignment.
The reason is that gimple_fold_builtin_memory_op created invalid GIMPLE,
because fold_ctor_reference called via fold_const_aggregate_ref was
discarding a cast, so it returned a different type than it got.  Fixed by
dropping useless type conversions only.

It also fixes a stale comment that I noticed.

Bootstrapped/regtested on x86_64-linux.  Preapproved by Jakub on IRC,
applying to trunk.

2015-04-09  Marek Polacek  <polacek@redhat.com>
	    Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/65554
	* gimple-fold.c (gimple_fold_builtin_memory_op): Update comment.
	(fold_ctor_reference): Use STRIP_USELESS_TYPE_CONVERSION instead
	of STRIP_NOPS.

	* g++.dg/opt/pr65554.C: New test.

diff --git gcc/gimple-fold.c gcc/gimple-fold.c
index f89220c..9458f96 100644
--- gcc/gimple-fold.c
+++ gcc/gimple-fold.c
@@ -769,7 +769,7 @@ var_decl_component_p (tree var)
 }
 
 /* Fold function call to builtin mem{{,p}cpy,move}.  Return
-   NULL_TREE if no simplification can be made.
+   false if no simplification can be made.
    If ENDP is 0, return DEST (like memcpy).
    If ENDP is 1, return DEST+LEN (like mempcpy).
    If ENDP is 2, return DEST+LEN-1 (like stpcpy).
@@ -5472,7 +5472,7 @@ fold_ctor_reference (tree type, tree ctor, unsigned HOST_WIDE_INT offset,
       ret = canonicalize_constructor_val (unshare_expr (ctor), from_decl);
       ret = fold_unary (VIEW_CONVERT_EXPR, type, ret);
       if (ret)
-	STRIP_NOPS (ret);
+	STRIP_USELESS_TYPE_CONVERSION (ret);
       return ret;
     }
   /* For constants and byte-aligned/sized reads try to go through
diff --git gcc/testsuite/g++.dg/opt/pr65554.C gcc/testsuite/g++.dg/opt/pr65554.C
index e69de29..70e43a4 100644
--- gcc/testsuite/g++.dg/opt/pr65554.C
+++ gcc/testsuite/g++.dg/opt/pr65554.C
@@ -0,0 +1,124 @@
+// PR middle-end/65554
+// { dg-do compile { target c++11 } }
+// { dg-options "-O" }
+
+namespace std
+{
+  struct B { enum { __value }; };
+  template <typename _Iterator> struct C
+  {
+    static _Iterator _S_base (_Iterator p1) { return p1; }
+  };
+  template <typename> using _RequireInputIter = int;
+  template <typename _Iterator> _Iterator __niter_base (_Iterator p1)
+  {
+    return std::C <_Iterator>::_S_base (p1);
+  }
+  template <typename _Iterator> _Iterator __miter_base (_Iterator p1)
+  {
+    return std::C <_Iterator>::_S_base (p1);
+  }
+  struct D
+  {
+    template <typename _Tp> static _Tp *__copy_m (_Tp * p1, _Tp * p2, _Tp *)
+    {
+      int _Num = p2 - p1;
+      __builtin_memmove (0, p1, sizeof (_Tp) * _Num);
+    }
+  };
+  template <int, typename _II, typename _OI> void __copy_move_a (_II p1, _II p2, _OI p3)
+  {
+    D::__copy_m (p1, p2, p3);
+  }
+  template <int, typename _II, typename _OI> void __copy_move_a2 (_II p1, _II p2, _OI p3)
+  {
+    __copy_move_a <0> (std::__niter_base (p1), std::__niter_base (p2), std::__niter_base (p3));
+  }
+  template <typename _II, typename _OI> void copy (_II p1, _II p2, _OI p3)
+  {
+    __copy_move_a2 <B::__value> (std::__miter_base (p1), std::__miter_base (p2), p3);
+  }
+}
+template <typename _Tp> struct F { typedef _Tp *pointer; };
+namespace std
+{
+  template <typename _Tp> using __allocator_base = F <_Tp>;
+  template <typename _Tp> struct allocator:__allocator_base <_Tp> {};
+  template <class _E> struct initializer_list
+  {
+    typedef _E *const_iterator;
+    _E *_M_array;
+    unsigned long _M_len;
+    const_iterator begin () { return _M_array; }
+    const_iterator end () { return begin () + 1; }
+  };
+  template <typename _Alloc> struct allocator_traits
+  {
+    template <typename _Tp> static typename _Tp::pointer _S_pointer_helper (_Tp *);
+    typedef decltype (_S_pointer_helper ((_Alloc *) 0)) __pointer;
+    typedef __pointer pointer;
+  };
+}
+template <typename> struct __alloc_traits:
+std::allocator_traits <std::allocator <const char *>> {};
+namespace std
+{
+  struct G
+  {
+    template <typename _InputIterator, typename _ForwardIterator> static _ForwardIterator __uninit_copy (_InputIterator p1, _InputIterator p2, _ForwardIterator p3)
+    {
+      copy (p1, p2, p3);
+    }
+  };
+  template <typename _InputIterator, typename _ForwardIterator> void
+  uninitialized_copy (_InputIterator p1, _InputIterator p2, _ForwardIterator p3)
+  {
+    G::__uninit_copy (p1, p2, p3);
+  }
+  template <typename _InputIterator, typename _ForwardIterator, typename _Tp> void __uninitialized_copy_a (_InputIterator p1, _InputIterator p2, _ForwardIterator p3, allocator <_Tp> &)
+  {
+    uninitialized_copy (p1, p2, p3);
+  }
+  struct H
+  {
+    typedef std::allocator <int *> _Tp_alloc_type;
+    typedef __alloc_traits <_Tp_alloc_type>::pointer pointer;
+    _Tp_alloc_type & _M_get_Tp_allocator ();
+  };
+  template <typename _Tp, typename = std::allocator <_Tp>> struct J: H
+  {
+    void operator= (initializer_list <_Tp> p1)
+    {
+      this->assign (p1.begin (), p1.end ());
+    }
+    template <typename _InputIterator, typename = std::_RequireInputIter <_InputIterator>> void assign (_InputIterator p1, _InputIterator p2)
+    {
+      _M_assign_dispatch (p1, p2, 0);
+    }
+    pointer _M_allocate_and_copy___result;
+    template <typename _ForwardIterator> void _M_allocate_and_copy (int, _ForwardIterator p2, _ForwardIterator p3)
+    {
+      __uninitialized_copy_a (p2, p3, _M_allocate_and_copy___result, _M_get_Tp_allocator ());
+    }
+    template <typename _InputIterator> void _M_assign_dispatch (_InputIterator p1, _InputIterator p2, int)
+    {
+      _M_assign_aux (p1, p2, 0);
+    }
+    template <typename _ForwardIterator> void _M_assign_aux (_ForwardIterator, _ForwardIterator, int);
+  };
+  template <typename _Tp, typename _Alloc>
+    template <typename _ForwardIterator> void J <_Tp, _Alloc>::_M_assign_aux (_ForwardIterator p1, _ForwardIterator p2, int)
+  {
+    _M_allocate_and_copy (0, p1, p2);
+  }
+  class I
+  {
+    void tabCompletion (std::J <int>&) const;
+  };
+  void
+  I::tabCompletion (J <int>&) const
+  {
+    J <const char *> extra;
+    extra = { "foo" };
+  }
+}

	Marek