[PATCH] D41746: Make std::get_temporary_buffer respect overaligned types when possible

[Chris Kennelly via Phabricator via cfe-commits]

ckennelly created this revision.
ckennelly added reviewers: EricWF, mclow.lists.

Repository:
  rCXX libc++

https://reviews.llvm.org/D41746

Files:
  include/memory
  test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp


Index: test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
===================================================================
--- /dev/null
+++ 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);
+}
Index: include/memory
===================================================================
--- include/memory
+++ include/memory
@@ -2003,7 +2003,31 @@
         __n = __m;
     while (__n > 0)
     {
+#if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
+        if (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
+        {
+            std::align_val_t __al = std::align_val_t(alignof(_Tp));
+            __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 (__alignof__(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
+#else
+        if (__alignof__(_Tp) > __alignof__(std::max_align_t))
+#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;
@@ -2016,7 +2040,18 @@
 
 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 (alignof(_Tp) > __STDCPP_DEFAULT_NEW_ALIGNMENT__)
+    {
+        std::align_val_t __al = std::align_val_t(alignof(_Tp));
+        ::operator delete(__p, __al);
+        return;
+    }
+#endif
+    ::operator delete(__p);
+}
 
 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
 template <class _Tp>


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