Make std::get_temporary_buffer respect overaligned types when possible

Patch by Chris Kennelly!

Differential Revision: https://reviews.llvm.org/D41746


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@324020 91177308-0d34-0410-b5e6-96231b3b80d8

include/memory

@@ -2004,7 +2004,38 @@ get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT
         __n = __m;
     while (__n > 0)
     {
+#if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
+#if defined(__STDCPP_DEFAULT_NEW_ALIGNMENT__)
+        if (std::alignment_of<_Tp>::value > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
+#else
+        if (std::alignment_of<_Tp>::value >
+            std::alignment_of<std::max_align_t>::value)
+#endif
+        {
+            std::align_val_t __al =
+                std::align_val_t(std::alignment_of<_Tp>::value);
+            __r.first = static_cast<_Tp*>(::operator new(
+                __n * sizeof(_Tp), __al, nothrow));
+        } else {
+            __r.first = static_cast<_Tp*>(::operator new(
+                __n * sizeof(_Tp), nothrow));
+        }
+#else
+#if defined(__STDCPP_DEFAULT_NEW_ALIGNMENT__)
+        if (std::alignment_of<_Tp>::value > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
+#else
+        if (std::alignment_of<_Tp>::value >
+            std::alignment_of<std::max_align_t>::value)
+#endif
+        {
+            // Since aligned operator new is unavailable, return an empty
+            // buffer rather than one with invalid alignment.
+            return __r;
+        }
+
         __r.first = static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), nothrow));
+#endif
+
         if (__r.first)
         {
             __r.second = __n;
@@ -2017,7 +2048,23 @@ get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT
 
 template <class _Tp>
 inline _LIBCPP_INLINE_VISIBILITY
-void return_temporary_buffer(_Tp* __p) _NOEXCEPT {::operator delete(__p);}
+void return_temporary_buffer(_Tp* __p) _NOEXCEPT
+{
+#if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
+#if defined(__STDCPP_DEFAULT_NEW_ALIGNMENT__)
+    if (std::alignment_of<_Tp>::value > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
+#else
+    if (std::alignment_of<_Tp>::value >
+        std::alignment_of<std::max_align_t>::value)
+#endif
+    {
+        std::align_val_t __al = std::align_val_t(std::alignment_of<_Tp>::value);
+        ::operator delete(__p, __al);
+        return;
+    }
+#endif
+    ::operator delete(__p);
+}
 
 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
 template <class _Tp>

test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp

@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <memory>
+
+// template <class T>
+//   pair<T*, ptrdiff_t>
+//   get_temporary_buffer(ptrdiff_t n);
+//
+// template <class T>
+//   void
+//   return_temporary_buffer(T* p);
+
+#include <memory>
+#include <cassert>
+
+struct alignas(32) A {
+    int field;
+};
+
+int main()
+{
+    std::pair<A*, std::ptrdiff_t> ip = std::get_temporary_buffer<A>(5);
+    assert(!(ip.first == nullptr) ^ (ip.second == 0));
+    assert(reinterpret_cast<uintptr_t>(ip.first) % alignof(A) == 0);
+    std::return_temporary_buffer(ip.first);
+}