Create subobject value in pretty printer

Nowadays, we create a value of subobject in pretty printer with 'address'
being used,

  value = value_from_contents_and_address (type, valaddr + embedded_offset,
					   address + embedded_offset);

  set_value_component_location (value, val);
  /* set_value_component_location resets the address, so we may
     need to set it again.  */
  if (VALUE_LVAL (value) != lval_internalvar
      && VALUE_LVAL (value) != lval_internalvar_component
      && VALUE_LVAL (value) != lval_computed)
    set_value_address (value, address + embedded_offset);

value_from_contents_and_address creates a value from memory, but the
value we are pretty-printing may not from memory at all.

Instead of using value_from_contents_and_address, we create a value
of subobject with the same location as object's but different offset.
We avoid using address in this way.  As a result, parameter 'address'
in apply_val_pretty_printer is no longer needed, we can remove it in
next step.

We've already had the location of the 'whole' value, so it is safe
to assume we can create a value of 'component' or 'suboject' value
at the same location but with different offset.

gdb:

2016-11-21  Yao Qi  <yao.qi@linaro.org>

	* guile/scm-pretty-print.c (gdbscm_apply_val_pretty_printer):
	Don't call value_from_contents_and_address and
	set_value_address.  Call value_from_component.
	* python/py-prettyprint.c (gdbpy_apply_val_pretty_printer):
	Likewise.
	* value.c (value_from_component): New function.
	* value.h (value_from_component): Likewise.
	* valarith.c (value_subscripted_rvalue): Call
	value_from_component.

1 files changed, 25 insertions, 0 deletions

diff --git a/gdb/value.c b/gdb/value.c
index 0575a55..200d61d 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -3795,6 +3795,31 @@ value_from_history_ref (const char *h, const char **endp)
   return access_value_history (index);
 }
 
+/* Get the component value (offset by OFFSET bytes) of a struct or
+   union WHOLE.  Component's type is TYPE.  */
+
+struct value *
+value_from_component (struct value *whole, struct type *type, LONGEST offset)
+{
+  struct value *v;
+
+  if (VALUE_LVAL (whole) == lval_memory && value_lazy (whole))
+    v = allocate_value_lazy (type);
+  else
+    {
+      v = allocate_value (type);
+      value_contents_copy (v, value_embedded_offset (v),
+			   whole, value_embedded_offset (whole) + offset,
+			   type_length_units (type));
+    }
+  v->offset = value_offset (whole) + offset + value_embedded_offset (whole);
+  set_value_component_location (v, whole);
+  VALUE_REGNUM (v) = VALUE_REGNUM (whole);
+  VALUE_FRAME_ID (v) = VALUE_FRAME_ID (whole);
+
+  return v;
+}
+
 struct value *
 coerce_ref_if_computed (const struct value *arg)
 {