Add scoped_value_mark

This adds a scoped_value_mark class, that records the value mark in
the constructor and then calls value_free_to_mark in the destructor.
It then updates various spots in gdb to use this class, rather than a
cleanup.

It would be better overall to replace "struct value *" with a
shared_ptr, maybe eliminating the need for this class (watchpoints
would perhaps need some new mechanism as well).  However, that's
difficult to do.

2017-01-10  Tom Tromey  <tom@tromey.com>

	* python/py-value.c (valpy_dereference, valpy_referenced_value)
	(valpy_reference_value, valpy_const_value, valpy_get_address)
	(valpy_get_dynamic_type, valpy_lazy_string, valpy_do_cast)
	(valpy_getitem, valpy_call, valpy_binop_throw, valpy_negative)
	(valpy_absolute, valpy_richcompare_throw): Use scoped_value_mark.
	* dwarf2loc.c (dwarf2_loc_desc_get_symbol_read_needs): Use
	scoped_value_mark.
	* dwarf2-frame.c (execute_stack_op): Use scoped_value_mark.
	* value.h (scoped_value_mark): New class.

1 files changed, 22 insertions, 0 deletions

diff --git a/gdb/value.h b/gdb/value.h
index 4aba8c0a41..0c5ab284b3 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -714,6 +714,28 @@ extern struct value *value_mark (void);
 
 extern void value_free_to_mark (const struct value *mark);
 
+/* A helper class that uses value_mark at construction time and calls
+   value_free_to_mark in the destructor.  This is used to clear out
+   temporary values created during the lifetime of this object.  */
+class scoped_value_mark
+{
+ public:
+
+  scoped_value_mark ()
+    : m_value (value_mark ())
+  {
+  }
+
+  ~scoped_value_mark ()
+  {
+    value_free_to_mark (m_value);
+  }
+
+ private:
+
+  const struct value *m_value;
+};
+
 extern struct value *value_cstring (const char *ptr, ssize_t len,
 				    struct type *char_type);
 extern struct value *value_string (const char *ptr, ssize_t len,