PR10594: Provide a cached dwarf_getscopes_die

This avoids repeated DIE traversal by caching all parents on the first
call, so future calls are just a simple walk up parent links.

* dwflpp.cxx (dwflpp::getscopes_die): New cached function that mimics
  libdw's dwarf_getscopes_die using cached parent links.
  (dwflpp::cache_die_parents): New function to build the parent cache.
  (dwflpp::~dwflpp): Clean up the parent caches.
  (dwflpp::iterate_over_labels): Use the cached getscopes_die.
  (dwflpp::find_variable_and_frame_base): Ditto.
* tapsets.cxx (dwarf_derived_probe::saveargs): Ditto.
  (uprobe_derived_probe::saveargs): Ditto.
  (dwarf_var_expanding_visitor::visit_target_symbol_context): Ditto.

1 files changed, 11 insertions, 0 deletions

diff --git a/dwflpp.h b/dwflpp.h
index 74a3ae00..e047fcba 100644
--- a/dwflpp.h
+++ b/dwflpp.h
@@ -65,6 +65,12 @@ typedef unordered_map<void*, cu_function_cache_t*> mod_cu_function_cache_t;
 // inline function die -> instance die[]
 typedef unordered_map<void*, std::vector<Dwarf_Die>*> cu_inl_function_cache_t;
 
+// die -> parent die
+typedef unordered_map<void*, Dwarf_Die> cu_die_parent_cache_t;
+
+// cu die -> (die -> parent die)
+typedef unordered_map<void*, cu_die_parent_cache_t*> mod_cu_die_parent_cache_t;
+
 typedef std::vector<func_info> func_info_map_t;
 typedef std::vector<inline_instance_info> inline_instance_map_t;
 
@@ -201,6 +207,8 @@ struct dwflpp
   void iterate_over_inline_instances (int (* callback)(Dwarf_Die * die, void * arg),
                                       void * data);
 
+  std::vector<Dwarf_Die> getscopes_die(Dwarf_Die* die);
+
   Dwarf_Die *declaration_resolve(const char *name);
 
   mod_cu_function_cache_t cu_function_cache;
@@ -292,6 +300,9 @@ private:
   cu_inl_function_cache_t cu_inl_function_cache;
   void cache_inline_instances (Dwarf_Die* die);
 
+  mod_cu_die_parent_cache_t cu_die_parent_cache;
+  void cache_die_parents(cu_die_parent_cache_t* parents, Dwarf_Die* die);
+
   /* The global alias cache is used to resolve any DIE found in a
    * module that is stubbed out with DW_AT_declaration with a defining
    * DIE found in a different module.  The current assumption is that