Re: [C++ PATCH] PR c++/35878

[Ville Voutilainen]

On 21 March 2017 at 02:46, Ville Voutilainen
<ville.voutilai...@gmail.com> wrote:
> On 21 March 2017 at 02:43, Ville Voutilainen
> <ville.voutilai...@gmail.com> wrote:
>> Hmm. I should either rename that function or flip its logic. Now it's
>> a bit backwards. :) I'll flip its logic.
>
> In other words, see attached.

Let's call the function what it really is.

2017-03-21  Ville Voutilainen  <ville.voutilai...@gmail.com>

    gcc/

    PR c++/35878
    * cp/init.c (std_placement_new_fn_p): New.
    (build_new_1): Call it.

    testsuite/

    PR c++/35878
    * g++.dg/init/pr35878_1.C: New.
    * g++.dg/init/pr35878_2.C: Likewise.
    * g++.dg/init/pr35878_3.C: Likewise.

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index 8bfcbde..a0cd64c 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -2693,6 +2693,21 @@ malloc_alignment ()
   return MAX (max_align_t_align(), MALLOC_ABI_ALIGNMENT);
 }
 
+/* Determine whether an allocation function is a namespace-scope
+   non-replaceable placement new function. See DR 1748.
+   TODO: Enable in all standard modes.  */
+static bool std_placement_new_fn_p (tree alloc_fn)
+{
+  if ((cxx_dialect > cxx14) && DECL_NAMESPACE_SCOPE_P (alloc_fn))
+    {
+      tree first_arg = TREE_CHAIN (TYPE_ARG_TYPES (TREE_TYPE (alloc_fn)));
+      if ((TREE_VALUE (first_arg) == ptr_type_node)
+         && TREE_CHAIN (first_arg) == void_list_node)
+       return true;
+    }
+  return false;
+}
+
 /* Generate code for a new-expression, including calling the "operator
    new" function, initializing the object, and, if an exception occurs
    during construction, cleaning up.  The arguments are as for
@@ -3171,7 +3186,8 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, 
tree nelts,
      So check for a null exception spec on the op new we just called.  */
 
   nothrow = TYPE_NOTHROW_P (TREE_TYPE (alloc_fn));
-  check_new = (flag_check_new || nothrow);
+  check_new = flag_check_new
+    || (nothrow && !std_placement_new_fn_p (alloc_fn));
 
   if (cookie_size)
     {
diff --git a/gcc/testsuite/g++.dg/init/pr35878_1.C 
b/gcc/testsuite/g++.dg/init/pr35878_1.C
new file mode 100644
index 0000000..b45c009
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/pr35878_1.C
@@ -0,0 +1,21 @@
+// { dg-options "-O2 --std=gnu++11" }
+// { dg-do compile }
+// { dg-final { scan-assembler "test.*%rdi, %rdi" { target i?86-*-* x86_64-*-* 
} } }
+#include <new>
+#include <utility>
+
+struct s1{
+  int a;
+  int b;
+  int c;
+};
+
+void f1 (s1 * v, s1&& s)
+{
+       new (v) s1(std::move(s));
+}
+
+void f2 (s1 * v, s1&& s)
+{
+       *v = std::move(s);
+}
diff --git a/gcc/testsuite/g++.dg/init/pr35878_2.C 
b/gcc/testsuite/g++.dg/init/pr35878_2.C
new file mode 100644
index 0000000..0664494
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/pr35878_2.C
@@ -0,0 +1,21 @@
+// { dg-options "-O2 --std=gnu++17 -fcheck-new" }
+// { dg-do compile }
+// { dg-final { scan-assembler "test.*%rdi, %rdi" { target i?86-*-* x86_64-*-* 
} } }
+#include <new>
+#include <utility>
+
+struct s1{
+  int a;
+  int b;
+  int c;
+};
+
+void f1 (s1 * v, s1&& s)
+{
+       new (v) s1(std::move(s));
+}
+
+void f2 (s1 * v, s1&& s)
+{
+       *v = std::move(s);
+}
diff --git a/gcc/testsuite/g++.dg/init/pr35878_3.C 
b/gcc/testsuite/g++.dg/init/pr35878_3.C
new file mode 100644
index 0000000..8a5614f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/pr35878_3.C
@@ -0,0 +1,21 @@
+// { dg-options "-O2 --std=gnu++17" }
+// { dg-do compile }
+// { dg-final { scan-assembler-not "test.*%rdi, %rdi" { target i?86-*-* 
x86_64-*-* } } }
+#include <new>
+#include <utility>
+
+struct s1{
+  int a;
+  int b;
+  int c;
+};
+
+void f1 (s1 * v, s1&& s)
+{
+       new (v) s1(std::move(s));
+}
+
+void f2 (s1 * v, s1&& s)
+{
+       *v = std::move(s);
+}