[PATCH] D25042: [libc++] Clarify _LIBCPP_NEW_DELETE_VIS for Windows

Shoaib Meenai via cfe-commits cfe-commits at lists.llvm.org
Wed Sep 28 15:12:12 PDT 2016

smeenai updated this revision to Diff 72911.
smeenai added a comment.

Moving documentation to documentation file, per @EricWF's comment



Index: include/new
--- include/new
+++ include/new
@@ -125,8 +125,8 @@
 }  // std
-#if defined(_WIN32) && !defined(cxx_EXPORTS)
+#if defined(_LIBCPP_MSVCRT) && !defined(_LIBCPP_BUILDING_LIBRARY)
Index: docs/DesignDocs/VisibilityMacros.rst
--- docs/DesignDocs/VisibilityMacros.rst
+++ docs/DesignDocs/VisibilityMacros.rst
@@ -108,6 +108,19 @@
   versioning namespace. This allows throwing and catching some exception types
   between libc++ and libstdc++.
+  Mark a symbol as being exported by the libc++ library. This macro must be
+  applied to all `operator new` and `operator delete` overloads.
+  **Windows Behavior**: When using the Microsoft CRT, all the `operator new` and
+  `operator delete` overloads are defined statically in `msvcrt.lib`. Marking
+  them as `dllimport` in the libc++ `<new>` header is therefore undesirable: if
+  we were to mark them as `dllimport` and then link against libc++, source files
+  which included `<new>` would end up linking against libc++'s `operator new`
+  and `operator delete`, while source files which did not include `<new>` would
+  end up linking against msvcrt's `operator new` and `operator delete`, which
+  would be a confusing and potentially error-prone inconsistency.

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