Use scoped_value_mark in dwarf2_evaluate_loc_desc_full

This changes dwarf2_evaluate_loc_desc_full to use scoped_value_mark.

Note that this function previously called do_cleanup using the same
cleanup multiple times.  I had thought this was buggy, but re-reading
make_my_cleanup2 indicates that it is not.  Nevertheless it is
surprising, and at least one of the calls (the one that is completely
removed in this patch) seems to have been done under the assumption
that it would still have some effect.

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

	* value.h (scoped_value_mark::~scoped_value_mark): Call
	free_to_mark.
	(scoped_value_mark::free_to_mark): New method.
	* dwarf2loc.c (dwarf2_evaluate_loc_desc_full): Use
	scoped_value_mark.

3 files changed, 32 insertions, 15 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 6922406..aaad4f8 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,13 @@
 2017-01-10  Tom Tromey  <tom@tromey.com>
 
+	* value.h (scoped_value_mark::~scoped_value_mark): Call
+	free_to_mark.
+	(scoped_value_mark::free_to_mark): New method.
+	* dwarf2loc.c (dwarf2_evaluate_loc_desc_full): Use
+	scoped_value_mark.
+
+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)
diff --git a/gdb/dwarf2loc.c b/gdb/dwarf2loc.c
index 633a459..7fca76b 100644
--- a/gdb/dwarf2loc.c
+++ b/gdb/dwarf2loc.c
@@ -2272,7 +2272,6 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 			       LONGEST byte_offset)
 {
   struct value *retval;
-  struct cleanup *value_chain;
   struct objfile *objfile = dwarf2_per_cu_objfile (per_cu);
 
   if (byte_offset < 0)
@@ -2286,7 +2285,7 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
   ctx.per_cu = per_cu;
   ctx.obj_address = 0;
 
-  value_chain = make_cleanup_value_free_to_mark (value_mark ());
+  scoped_value_mark free_values;
 
   ctx.gdbarch = get_objfile_arch (objfile);
   ctx.addr_size = dwarf2_per_cu_addr_size (per_cu);
@@ -2301,7 +2300,7 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
     {
       if (ex.error == NOT_AVAILABLE_ERROR)
 	{
-	  do_cleanups (value_chain);
+	  free_values.free_to_mark ();
 	  retval = allocate_value (type);
 	  mark_value_bytes_unavailable (retval, 0, TYPE_LENGTH (type));
 	  return retval;
@@ -2310,7 +2309,7 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 	{
 	  if (entry_values_debug)
 	    exception_print (gdb_stdout, ex);
-	  do_cleanups (value_chain);
+	  free_values.free_to_mark ();
 	  return allocate_optimized_out_value (type);
 	}
       else
@@ -2333,7 +2332,7 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 				  ctx.addr_size, frame);
       /* We must clean up the value chain after creating the piece
 	 closure but before allocating the result.  */
-      do_cleanups (value_chain);
+      free_values.free_to_mark ();
       retval = allocate_computed_value (type, &pieced_value_funcs, c);
       set_value_offset (retval, byte_offset);
     }
@@ -2350,7 +2349,7 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 
 	    if (byte_offset != 0)
 	      error (_("cannot use offset on synthetic pointer to register"));
-	    do_cleanups (value_chain);
+	    free_values.free_to_mark ();
 	    retval = value_from_register (type, gdb_regnum, frame);
 	    if (value_optimized_out (retval))
 	      {
@@ -2362,7 +2361,6 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 		   inspecting a register ($pc, $sp, etc.), return a
 		   generic optimized out value instead, so that we show
 		   <optimized out> instead of <not saved>.  */
-		do_cleanups (value_chain);
 		tmp = allocate_value (type);
 		value_contents_copy (tmp, 0, retval, 0, TYPE_LENGTH (type));
 		retval = tmp;
@@ -2396,7 +2394,7 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 	      }
 	    address = value_as_address (value_from_pointer (ptr_type, address));
 
-	    do_cleanups (value_chain);
+	    free_values.free_to_mark ();
 	    retval = value_at_lazy (type, address + byte_offset);
 	    if (in_stack_memory)
 	      set_value_stack (retval, 1);
@@ -2409,6 +2407,7 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 	    gdb_byte *contents;
 	    const gdb_byte *val_bytes;
 	    size_t n = TYPE_LENGTH (value_type (value));
+	    struct cleanup *cleanup;
 
 	    if (byte_offset + TYPE_LENGTH (type) > n)
 	      invalid_synthetic_pointer ();
@@ -2421,8 +2420,8 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 	       to the mark, but we still need the value contents
 	       below.  */
 	    value_incref (value);
-	    do_cleanups (value_chain);
-	    make_cleanup_value_free (value);
+	    free_values.free_to_mark ();
+	    cleanup = make_cleanup_value_free (value);
 
 	    retval = allocate_value (type);
 	    contents = value_contents_raw (retval);
@@ -2435,6 +2434,8 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 		n = TYPE_LENGTH (type);
 	      }
 	    memcpy (contents, val_bytes, n);
+
+	    do_cleanups (cleanup);
 	  }
 	  break;
 
@@ -2447,7 +2448,7 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 	    if (byte_offset + TYPE_LENGTH (type) > n)
 	      invalid_synthetic_pointer ();
 
-	    do_cleanups (value_chain);
+	    free_values.free_to_mark ();
 	    retval = allocate_value (type);
 	    contents = value_contents_raw (retval);
 
@@ -2467,7 +2468,7 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 	  break;
 
 	case DWARF_VALUE_OPTIMIZED_OUT:
-	  do_cleanups (value_chain);
+	  free_values.free_to_mark ();
 	  retval = allocate_optimized_out_value (type);
 	  break;
 
@@ -2483,8 +2484,6 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 
   set_value_initialized (retval, ctx.initialized);
 
-  do_cleanups (value_chain);
-
   return retval;
 }
 
diff --git a/gdb/value.h b/gdb/value.h
index 0c5ab28..c57ea79 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -728,7 +728,17 @@ class scoped_value_mark
 
   ~scoped_value_mark ()
   {
-    value_free_to_mark (m_value);
+    free_to_mark ();
+  }
+
+  /* Free the values currently on the value stack.  */
+  void free_to_mark ()
+  {
+    if (m_value != NULL)
+      {
+	value_free_to_mark (m_value);
+	m_value = NULL;
+      }
   }
 
  private: