Add workaround for aligned_alloc bug on AIX

diff --git a/libstdc++-v3/libsupc++/new_opa.cc b/libstdc++-v3/libsupc++/new_opa.cc
index 097280d9b54..7c4bb79cdab 100644
--- a/libstdc++-v3/libsupc++/new_opa.cc
+++ b/libstdc++-v3/libsupc++/new_opa.cc
@@ -95,6 +95,12 @@  operator new (std::size_t sz, std::align_val_t al)
     sz = 1;
 
 #if _GLIBCXX_HAVE_ALIGNED_ALLOC
+# ifdef _AIX
+  /* AIX 7.2.0.0 aligned_alloc incorrectly has posix_memalign's requirement
+   * that alignment is a multiple of sizeof(void*).  */
+  if (align < sizeof(void*))
+    align = sizeof(void*);
+# endif
   /* C11: the value of size shall be an integral multiple of alignment.  */
   if (std::size_t rem = sz & (align - 1))
     sz += align - rem;
diff --git a/libstdc++-v3/testsuite/18_support/new_aligned.cc b/libstdc++-v3/testsuite/18_support/new_aligned.cc
new file mode 100644
index 00000000000..a9f539d36e8
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/new_aligned.cc
@@ -0,0 +1,119 @@ 
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target c++17 } }
+
+#include <new>
+#include <memory>
+#include <testsuite_hooks.h>
+
+struct Test
+{
+  Test(std::size_t size, std::size_t a)
+  : size(size), alignment(std::align_val_t{a}),
+    p(::operator new(size, alignment))
+  { }
+
+  ~Test() { ::operator delete(p, size, alignment); }
+
+  std::size_t size;
+  std::align_val_t alignment;
+  void* p;
+
+  bool valid() const { return p != nullptr; }
+
+  bool aligned() const
+  {
+    auto ptr = p;
+    auto space = size;
+    return std::align((std::size_t)alignment, size, ptr, space) == p;
+  }
+};
+
+// operator new(size_t size, align_val_t alignment) has
+// undefined behaviour if the alignment argument is not
+// a valid alignment value (i.e. not a power of two).
+//
+// Unlike posix_memalign there is no requirement that
+// alignment >= sizeof(void*).
+//
+// Unlike aligned_alloc there is no requirement that
+// size is an integer multiple of alignment.
+
+void
+test01()
+{
+  // Test small values that would not be valid for
+  // posix_memalign or aligned_alloc.
+
+  Test t11{1, 1};
+  VERIFY( t11.valid() );
+  VERIFY( t11.aligned() );
+
+  Test t21{2, 1};
+  VERIFY( t21.valid() );
+  VERIFY( t21.aligned() );
+
+  Test t12{1, 2};
+  VERIFY( t12.valid() );
+  VERIFY( t12.aligned() );
+
+  Test t22{2, 2};
+  VERIFY( t22.valid() );
+  VERIFY( t22.aligned() );
+
+  Test t32{3, 2};
+  VERIFY( t32.valid() );
+  VERIFY( t32.aligned() );
+
+  Test t42{4, 2};
+  VERIFY( t42.valid() );
+  VERIFY( t42.aligned() );
+
+  Test t24{2, 4};
+  VERIFY( t24.valid() );
+  VERIFY( t24.aligned() );
+
+  Test t34{3, 4};
+  VERIFY( t34.valid() );
+  VERIFY( t34.aligned() );
+
+  Test t44{4, 4};
+  VERIFY( t44.valid() );
+  VERIFY( t44.aligned() );
+
+  // Test some larger values.
+
+  Test t128_16{128, 16};
+  VERIFY( t128_16.valid() );
+  VERIFY( t128_16.aligned() );
+
+  Test t128_64{128, 64};
+  VERIFY( t128_64.valid() );
+  VERIFY( t128_64.aligned() );
+
+  Test t64_128{64, 128};
+  VERIFY( t64_128.valid() );
+  VERIFY( t64_128.aligned() );
+}
+
+int
+main()
+{
+  test01();
+}