This patch adds an RAII class for managing the lifetimes of objects
on an obstack. See the comments in the patch for more details and
example usage.
gcc/
* obstack-utils.h: New file.
---
gcc/obstack-utils.h | 86 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 86 insertions(+)
create mode 100644 gcc/obstack-utils.h
diff --git a/gcc/obstack-utils.h b/gcc/obstack-utils.h
new file mode 100644
index 00000000000..ee389f89923
--- /dev/null
+++ b/gcc/obstack-utils.h
@@ -0,0 +1,86 @@
+// Obstack-related utilities.
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of GCC.
+//
+// GCC 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.
+//
+// GCC 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 GCC; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+#ifndef GCC_OBSTACK_UTILS_H
+#define GCC_OBSTACK_UTILS_H
+
+// This RAII class automatically frees memory allocated on an obstack,
+// unless told not to via keep (). It automatically converts to an
+// obstack, so it can (optionally) be used in place of the obstack
+// to make the scoping clearer. For example:
+//
+// obstack_watermark watermark (ob);
+// auto *ptr1 = XOBNEW (watermark, struct1);
+// if (...)
+// // Frees ptr1.
+// return false;
+//
+// auto *ptr2 = XOBNEW (watermark, struct2);
+// if (...)
+// // Frees ptr1 and ptr2.
+// return false;
+//
+// // Retains ptr1 and ptr2.
+// watermark.keep ();
+//
+// auto *ptr3 = XOBNEW (watermark, struct3);
+// if (...)
+// // Frees ptr3.
+// return false;
+//
+// // Retains ptr3 (in addition to ptr1 and ptr2 above).
+// watermark.keep ();
+// return true;
+//
+// The move constructor makes it possible to transfer ownership to a caller:
+//
+// obstack_watermark
+// foo ()
+// {
+// obstack_watermark watermark (ob);
+// ...
+// return watermark;
+// }
+//
+// void
+// bar ()
+// {
+// // Inherit ownership of everything that foo allocated.
+// obstack_watermark watermark = foo ();
+// ...
+// }
+class obstack_watermark
+{
+public:
+ obstack_watermark (obstack *ob) : m_obstack (ob) { keep (); }
+ constexpr obstack_watermark (obstack_watermark &&) = default;
+ ~obstack_watermark () { obstack_free (m_obstack, m_start); }
+
+ operator obstack *() const { return m_obstack; }
+ void keep () { m_start = XOBNEWVAR (m_obstack, char, 0); }
+
+private:
+ DISABLE_COPY_AND_ASSIGN (obstack_watermark);
+
+protected:
+ obstack *m_obstack;
+ char *m_start;
+};
+
+#endif
--
2.17.1
