[RFC][Python] Re: any expression to tell whether a variable was optimized out?

[Thiago Jung Bauermann <bauerman at br dot ibm dot com>]

[ Moving thread from the gdb@ ml. ]

El mar, 17-03-2009 a las 15:06 -0600, Tom Tromey escribiÃ:
> >>>>> "Thiago" == Thiago Jung Bauermann <bauerman@br.ibm.com> writes:
> Thiago> You can also do the above by checking out the archer-tromey-python
> Thiago> branch, and applying the patch below. I didn't commit this yet because I
> Thiago> don't know if it would be better to have is_optimized_out function as a
> Thiago> method or attribute of gdb.Value...
> 
> I think attribute, because (AFAIK) it is immutable.
> 
> I'm a little surprised that this is an attribute of values at all.
> Doesn't that seem weird?  Is there anything useful that can be done
> with a value like this?  Perhaps just fetching its type?

I guess Alexandre just found a use for the attribute. :-)

This patch implements the attribute in gdb.Value, what do you think?

By the way, when writing this patch I realised that probably the
"address" method in Value would better be turned into an attribute.
Also, in the python branch, the "type" method also could be converted to
an attribute.
-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center


gdb/
	Add gdb.Value.is_optimized_out attribute.
	* python/python-value.c (valpy_get_is_optimized_out): New
	function.
	(value_object_getset): New variable.
	(value_object_type): Initialize tp_getset element.

gdb/doc/
	* gdb.texinfo (Values From Inferior): Document is_optimized_out
	attribute.

gdb/testsuite/
	* gdb.python/python-value.exp (test_value_in_inferior): Test
	gdb.Value.is_optimized_out attribute.

Index: gdb.git/gdb/python/python-value.c
===================================================================
--- gdb.git.orig/gdb/python/python-value.c	2009-03-22 22:19:11.000000000 -0300
+++ gdb.git/gdb/python/python-value.c	2009-03-22 22:19:13.000000000 -0300
@@ -272,6 +272,18 @@ valpy_str (PyObject *self)
   return result;
 }
 
+/* Implements gdb.Value.is_optimized_out.  */
+static PyObject *
+valpy_get_is_optimized_out (PyObject *self, void *closure)
+{
+  struct value *value = ((value_object *) self)->value;
+
+  if (value_optimized_out (value))
+    Py_RETURN_TRUE;
+
+  Py_RETURN_FALSE;
+}
+
 enum valpy_opcode
 {
   VALPY_ADD,
@@ -825,6 +837,13 @@ gdbpy_initialize_values (void)
   values_in_python = NULL;
 }
 
+static PyGetSetDef value_object_getset[] = {
+  { "is_optimized_out", valpy_get_is_optimized_out, NULL,
+    "Boolean telling whether the value is optimized out (i.e., not available).",
+    NULL },
+  {NULL}  /* Sentinel */
+};
+
 static PyMethodDef value_object_methods[] = {
   { "address", valpy_address, METH_NOARGS, "Return the address of the value." },
   { "dereference", valpy_dereference, METH_NOARGS, "Dereferences the value." },
@@ -897,7 +916,7 @@ PyTypeObject value_object_type = {
   0,				  /* tp_iternext */
   value_object_methods,		  /* tp_methods */
   0,				  /* tp_members */
-  0,				  /* tp_getset */
+  value_object_getset,		  /* tp_getset */
   0,				  /* tp_base */
   0,				  /* tp_dict */
   0,				  /* tp_descr_get */
Index: gdb.git/gdb/testsuite/gdb.python/python-value.exp
===================================================================
--- gdb.git.orig/gdb/testsuite/gdb.python/python-value.exp	2009-03-22 22:19:11.000000000 -0300
+++ gdb.git/gdb/testsuite/gdb.python/python-value.exp	2009-03-22 22:19:13.000000000 -0300
@@ -225,6 +225,9 @@ proc test_value_in_inferior {} {
 
   # Check that the dereferenced value is sane
   gdb_test "python print arg0" "0x.*$testfile\"" "verify dereferenced value"
+
+  # Smoke-test is_optimized_out attribute
+  gdb_test "python print 'result =', arg0.is_optimized_out" "= False" "Test is_optimized_out attribute"
 }
 
 
Index: gdb.git/gdb/doc/gdb.texinfo
===================================================================
--- gdb.git.orig/gdb/doc/gdb.texinfo	2009-03-22 22:19:11.000000000 -0300
+++ gdb.git/gdb/doc/gdb.texinfo	2009-03-22 22:24:46.000000000 -0300
@@ -18325,13 +18325,22 @@ bar = some_val['foo']
 
 Again, @code{bar} will also be a @code{gdb.Value} object.
 
-For pointer data types, @code{gdb.Value} provides a method for
-dereferencing the pointer to obtain the object it points to.
+The following attribute is provided:
 
+@table @code
+@defmethod Value is_optimized_out
+This read-only boolean attribute is true if the compiler optimized out
+this value, thus it is not available for fetching from the inferior.
+@end defmethod
+@end table
+
+The following methods are provided:
+
+@table @code
 @defmethod Value dereference
-This method returns a new @code{gdb.Value} object whose contents is
-the object pointed to by the pointer.  For example, if @code{foo} is
-a C pointer to an @code{int}, declared in your C program as
+For pointer data types, this method returns a new @code{gdb.Value} object
+whose contents is the object pointed to by the pointer.  For example, if
+@code{foo} is a C pointer to an @code{int}, declared in your C program as
 
 @smallexample
 int *foo;
@@ -18375,6 +18384,7 @@ will be used, if the current language is
 The optional @var{errors} argument is the same as the corresponding
 argument to Python's @code{string.decode} method.
 @end defmethod
+@end table
 
 @node Commands In Python
 @subsubsection Commands In Python