PR c++/77742 - -Waligned-new and placement new.

	* init.c (build_new_1): Don't -Waligned-new about placement new.
	(malloc_alignment): New.  Consider MALLOC_ABI_ALIGNMENT.
	* decl.c (cxx_init_decl_processing): New.

From-SVN: r241073

5 files changed, 50 insertions, 16 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index ff0435e..b01e196 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,10 @@
+2016-10-11  Jason Merrill  <jason@redhat.com>
+
+	PR c++/77742
+	* init.c (build_new_1): Don't -Waligned-new about placement new.
+	(malloc_alignment): New.  Consider MALLOC_ABI_ALIGNMENT.
+	* decl.c (cxx_init_decl_processing): New.
+
 2016-10-10  Jason Merrill  <jason@redhat.com>
 
 	PR c++/77890
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 8b0442f..88cae04 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -5953,6 +5953,7 @@ extern tree build_offset_ref			(tree, tree, bool,
 						 tsubst_flags_t);
 extern tree throw_bad_array_new_length		(void);
 extern bool type_has_new_extended_alignment	(tree);
+extern unsigned malloc_alignment		(void);
 extern tree build_new				(vec<tree, va_gc> **, tree, tree,
 						 vec<tree, va_gc> **, int,
                                                  tsubst_flags_t);
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 2d11aef..6240893 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -4082,7 +4082,7 @@ cxx_init_decl_processing (void)
   if (aligned_new_threshold == -1)
     aligned_new_threshold = (cxx_dialect >= cxx1z) ? 1 : 0;
   if (aligned_new_threshold == 1)
-    aligned_new_threshold = max_align_t_align () / BITS_PER_UNIT;
+    aligned_new_threshold = malloc_alignment () / BITS_PER_UNIT;
 
   {
     tree newattrs, extvisattr;
diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index b4b5e0a..455995a 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -2589,6 +2589,16 @@ type_has_new_extended_alignment (tree t)
 	  && TYPE_ALIGN_UNIT (t) > (unsigned)aligned_new_threshold);
 }
 
+/* Return the alignment we expect malloc to guarantee.  This should just be
+   MALLOC_ABI_ALIGNMENT, but that macro defaults to only BITS_PER_WORD for some
+   reason, so don't let the threshold be smaller than max_align_t_align.  */
+
+unsigned
+malloc_alignment ()
+{
+  return MAX (max_align_t_align(), MALLOC_ABI_ALIGNMENT);
+}
+
 /* 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
@@ -2974,8 +2984,23 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
 
   gcc_assert (alloc_fn != NULL_TREE);
 
+  /* Now, check to see if this function is actually a placement
+     allocation function.  This can happen even when PLACEMENT is NULL
+     because we might have something like:
+
+       struct S { void* operator new (size_t, int i = 0); };
+
+     A call to `new S' will get this allocation function, even though
+     there is no explicit placement argument.  If there is more than
+     one argument, or there are variable arguments, then this is a
+     placement allocation function.  */
+  placement_allocation_fn_p
+    = (type_num_arguments (TREE_TYPE (alloc_fn)) > 1
+       || varargs_function_p (alloc_fn));
+
   if (warn_aligned_new
-      && TYPE_ALIGN (elt_type) > max_align_t_align ()
+      && !placement_allocation_fn_p
+      && TYPE_ALIGN (elt_type) > malloc_alignment ()
       && (warn_aligned_new > 1
 	  || CP_DECL_CONTEXT (alloc_fn) == global_namespace)
       && !aligned_allocation_fn_p (alloc_fn))
@@ -3033,20 +3058,6 @@ build_new_1 (vec<tree, va_gc> **placement, tree type, tree nelts,
   while (TREE_CODE (alloc_call) == COMPOUND_EXPR)
     alloc_call = TREE_OPERAND (alloc_call, 1);
 
-  /* Now, check to see if this function is actually a placement
-     allocation function.  This can happen even when PLACEMENT is NULL
-     because we might have something like:
-
-       struct S { void* operator new (size_t, int i = 0); };
-
-     A call to `new S' will get this allocation function, even though
-     there is no explicit placement argument.  If there is more than
-     one argument, or there are variable arguments, then this is a
-     placement allocation function.  */
-  placement_allocation_fn_p
-    = (type_num_arguments (TREE_TYPE (alloc_fn)) > 1
-       || varargs_function_p (alloc_fn));
-
   /* Preevaluate the placement args so that we don't reevaluate them for a
      placement delete.  */
   if (placement_allocation_fn_p)
diff --git a/gcc/testsuite/g++.dg/cpp1z/aligned-new7.C b/gcc/testsuite/g++.dg/cpp1z/aligned-new7.C
new file mode 100644
index 0000000..e12db9b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/aligned-new7.C
@@ -0,0 +1,15 @@
+// PR c++/77742
+// { dg-options "-Wall -std=c++1z" }
+
+#include <new>
+
+struct X
+{
+  alignas(2*__STDCPP_DEFAULT_NEW_ALIGNMENT__) int i;
+};
+
+int main()
+{
+  alignas(alignof(X)) char buf[sizeof(X)];
+  ::new((void*)buf) X{1};
+}