gdb: pass frames as `const frame_info_ptr &`

We currently pass frames to function by value, as `frame_info_ptr`.
This is somewhat expensive:

 - the size of `frame_info_ptr` is 64 bytes, which is a bit big to pass
   by value
 - the constructors and destructor link/unlink the object in the global
   `frame_info_ptr::frame_list` list.  This is an `intrusive_list`, so
   it's not so bad: it's just assigning a few points, there's no memory
   allocation as if it was `std::list`, but still it's useless to do
   that over and over.

As suggested by Tom Tromey, change many function signatures to accept
`const frame_info_ptr &` instead of `frame_info_ptr`.

Some functions reassign their `frame_info_ptr` parameter, like:

  void
  the_func (frame_info_ptr frame)
  {
    for (; frame != nullptr; frame = get_prev_frame (frame))
      {
        ...
      }
  }

I wondered what to do about them, do I leave them as-is or change them
(and need to introduce a separate local variable that can be
re-assigned).  I opted for the later for consistency.  It might not be
clear why some functions take `const frame_info_ptr &` while others take
`frame_info_ptr`.  Also, if a function took a `frame_info_ptr` because
it did re-assign its parameter, I doubt that we would think to change it
to `const frame_info_ptr &` should the implementation change such that
it doesn't need to take `frame_info_ptr` anymore.  It seems better to
have a simple rule and apply it everywhere.

Change-Id: I59d10addef687d157f82ccf4d54f5dde9a963fd0
Approved-By: Andrew Burgess <aburgess@redhat.com>

1 files changed, 26 insertions, 25 deletions

diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c
index 0f0d14f..203ad53 100644
--- a/gdb/dwarf2/loc.c
+++ b/gdb/dwarf2/loc.c
@@ -48,7 +48,7 @@
 #include "gdbsupport/byte-vector.h"
 
 static struct value *dwarf2_evaluate_loc_desc_full
-  (struct type *type, frame_info_ptr frame, const gdb_byte *data,
+  (struct type *type, const frame_info_ptr &frame, const gdb_byte *data,
    size_t size, dwarf2_per_cu_data *per_cu, dwarf2_per_objfile *per_objfile,
    struct type *subobj_type, LONGEST subobj_byte_offset, bool as_lval = true);
 
@@ -503,7 +503,7 @@ locexpr_find_frame_base_location (struct symbol *framefunc, CORE_ADDR pc,
    LOC_BLOCK functions using a DWARF expression as its DW_AT_frame_base.  */
 
 static CORE_ADDR
-locexpr_get_frame_base (struct symbol *framefunc, frame_info_ptr frame)
+locexpr_get_frame_base (struct symbol *framefunc, const frame_info_ptr &frame)
 {
   struct gdbarch *gdbarch;
   struct type *type;
@@ -561,7 +561,7 @@ loclist_find_frame_base_location (struct symbol *framefunc, CORE_ADDR pc,
    LOC_BLOCK functions using a DWARF location list as its DW_AT_frame_base.  */
 
 static CORE_ADDR
-loclist_get_frame_base (struct symbol *framefunc, frame_info_ptr frame)
+loclist_get_frame_base (struct symbol *framefunc, const frame_info_ptr &frame)
 {
   struct gdbarch *gdbarch;
   struct type *type;
@@ -649,11 +649,10 @@ show_entry_values_debug (struct ui_file *file, int from_tty,
 /* See gdbtypes.h.  */
 
 void
-call_site_target::iterate_over_addresses
-     (struct gdbarch *call_site_gdbarch,
-      const struct call_site *call_site,
-      frame_info_ptr caller_frame,
-      iterate_ftype callback) const
+call_site_target::iterate_over_addresses (gdbarch *call_site_gdbarch,
+					  const call_site *call_site,
+					  const frame_info_ptr &caller_frame,
+					  iterate_ftype callback) const
 {
   switch (m_loc_kind)
     {
@@ -1138,9 +1137,9 @@ call_site_parameter_matches (struct call_site_parameter *parameter,
 /* See loc.h.  */
 
 struct call_site_parameter *
-dwarf_expr_reg_to_entry_parameter (frame_info_ptr frame,
-				   enum call_site_parameter_kind kind,
-				   union call_site_parameter_u kind_u,
+dwarf_expr_reg_to_entry_parameter (const frame_info_ptr &initial_frame,
+				   call_site_parameter_kind kind,
+				   call_site_parameter_u kind_u,
 				   dwarf2_per_cu_data **per_cu_return,
 				   dwarf2_per_objfile **per_objfile_return)
 {
@@ -1152,6 +1151,7 @@ dwarf_expr_reg_to_entry_parameter (frame_info_ptr frame,
   /* Initialize it just to avoid a GCC false warning.  */
   struct call_site_parameter *parameter = NULL;
   CORE_ADDR target_addr;
+  frame_info_ptr frame = initial_frame;
 
   while (get_frame_type (frame) == INLINE_FRAME)
     {
@@ -1263,7 +1263,7 @@ dwarf_expr_reg_to_entry_parameter (frame_info_ptr frame,
 static struct value *
 dwarf_entry_parameter_to_value (struct call_site_parameter *parameter,
 				CORE_ADDR deref_size, struct type *type,
-				frame_info_ptr caller_frame,
+				const frame_info_ptr &caller_frame,
 				dwarf2_per_cu_data *per_cu,
 				dwarf2_per_objfile *per_objfile)
 {
@@ -1339,7 +1339,7 @@ static const struct lval_funcs entry_data_value_funcs =
 
 /* See dwarf2/loc.h.  */
 struct value *
-value_of_dwarf_reg_entry (struct type *type, frame_info_ptr frame,
+value_of_dwarf_reg_entry (struct type *type, const frame_info_ptr &frame,
 			  enum call_site_parameter_kind kind,
 			  union call_site_parameter_u kind_u)
 {
@@ -1395,7 +1395,7 @@ value_of_dwarf_reg_entry (struct type *type, frame_info_ptr frame,
    cannot resolve the parameter for any reason.  */
 
 static struct value *
-value_of_dwarf_block_entry (struct type *type, frame_info_ptr frame,
+value_of_dwarf_block_entry (struct type *type, const frame_info_ptr &frame,
 			    const gdb_byte *block, size_t block_len)
 {
   union call_site_parameter_u kind_u;
@@ -1456,7 +1456,7 @@ struct value *
 indirect_synthetic_pointer (sect_offset die, LONGEST byte_offset,
 			    dwarf2_per_cu_data *per_cu,
 			    dwarf2_per_objfile *per_objfile,
-			    frame_info_ptr frame, struct type *type,
+			    const frame_info_ptr &frame, struct type *type,
 			    bool resolve_abstract_p)
 {
   /* Fetch the location expression of the DIE we're pointing to.  */
@@ -1496,7 +1496,7 @@ indirect_synthetic_pointer (sect_offset die, LONGEST byte_offset,
    SUBOBJ_BYTE_OFFSET within the variable of type TYPE.  */
 
 static struct value *
-dwarf2_evaluate_loc_desc_full (struct type *type, frame_info_ptr frame,
+dwarf2_evaluate_loc_desc_full (struct type *type, const frame_info_ptr &frame,
 			       const gdb_byte *data, size_t size,
 			       dwarf2_per_cu_data *per_cu,
 			       dwarf2_per_objfile *per_objfile,
@@ -1561,7 +1561,7 @@ dwarf2_evaluate_loc_desc_full (struct type *type, frame_info_ptr frame,
    passes 0 as the byte_offset.  */
 
 struct value *
-dwarf2_evaluate_loc_desc (struct type *type, frame_info_ptr frame,
+dwarf2_evaluate_loc_desc (struct type *type, const frame_info_ptr &frame,
 			  const gdb_byte *data, size_t size,
 			  dwarf2_per_cu_data *per_cu,
 			  dwarf2_per_objfile *per_objfile, bool as_lval)
@@ -1584,7 +1584,7 @@ dwarf2_evaluate_loc_desc (struct type *type, frame_info_ptr frame,
 
 static int
 dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
-			   frame_info_ptr frame,
+			   const frame_info_ptr &frame,
 			   const struct property_addr_info *addr_stack,
 			   CORE_ADDR *valp,
 			   gdb::array_view<CORE_ADDR> push_values,
@@ -1644,9 +1644,9 @@ dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
 /* See dwarf2/loc.h.  */
 
 bool
-dwarf2_evaluate_property (const struct dynamic_prop *prop,
-			  frame_info_ptr frame,
-			  const struct property_addr_info *addr_stack,
+dwarf2_evaluate_property (const dynamic_prop *prop,
+			  const frame_info_ptr &initial_frame,
+			  const property_addr_info *addr_stack,
 			  CORE_ADDR *value,
 			  gdb::array_view<CORE_ADDR> push_values)
 {
@@ -1657,6 +1657,7 @@ dwarf2_evaluate_property (const struct dynamic_prop *prop,
      Without this here this could happen if the code below selects a
      frame.  */
   scoped_restore_current_language save_language;
+  frame_info_ptr frame = initial_frame;
 
   if (frame == NULL && has_stack_frames ())
     frame = get_selected_frame (NULL);
@@ -3051,7 +3052,7 @@ dwarf2_compile_expr_to_ax (struct agent_expr *expr, struct axs_value *loc,
 /* Return the value of SYMBOL in FRAME using the DWARF-2 expression
    evaluator to calculate the location.  */
 static struct value *
-locexpr_read_variable (struct symbol *symbol, frame_info_ptr frame)
+locexpr_read_variable (struct symbol *symbol, const frame_info_ptr &frame)
 {
   struct dwarf2_locexpr_baton *dlbaton
     = (struct dwarf2_locexpr_baton *) SYMBOL_LOCATION_BATON (symbol);
@@ -3069,7 +3070,7 @@ locexpr_read_variable (struct symbol *symbol, frame_info_ptr frame)
    will be thrown.  */
 
 static struct value *
-locexpr_read_variable_at_entry (struct symbol *symbol, frame_info_ptr frame)
+locexpr_read_variable_at_entry (struct symbol *symbol, const frame_info_ptr &frame)
 {
   struct dwarf2_locexpr_baton *dlbaton
     = (struct dwarf2_locexpr_baton *) SYMBOL_LOCATION_BATON (symbol);
@@ -3884,7 +3885,7 @@ const struct symbol_computed_ops dwarf2_locexpr_funcs = {
 /* Return the value of SYMBOL in FRAME using the DWARF-2 expression
    evaluator to calculate the location.  */
 static struct value *
-loclist_read_variable (struct symbol *symbol, frame_info_ptr frame)
+loclist_read_variable (struct symbol *symbol, const frame_info_ptr &frame)
 {
   struct dwarf2_loclist_baton *dlbaton
     = (struct dwarf2_loclist_baton *) SYMBOL_LOCATION_BATON (symbol);
@@ -3909,7 +3910,7 @@ loclist_read_variable (struct symbol *symbol, frame_info_ptr frame)
    if it cannot resolve the parameter for any reason.  */
 
 static struct value *
-loclist_read_variable_at_entry (struct symbol *symbol, frame_info_ptr frame)
+loclist_read_variable_at_entry (struct symbol *symbol, const frame_info_ptr &frame)
 {
   struct dwarf2_loclist_baton *dlbaton
     = (struct dwarf2_loclist_baton *) SYMBOL_LOCATION_BATON (symbol);