[dwarf-reader] Optimize speed of compare_as_decl_dies

Profiling shows that the *number of calls* to
compare_dies_string_attribute_value by compare_as_decl_dies represents
a hotspot.  That is, compare_dies_string_attribute_value itself
doesn't necessarily takes long, but it's being called "too much",
especially when compare_as_decl_dies is called for DIEs representing
classes/structs.

This patch thus reduces the calls to
compare_dies_string_attribute_value from 3 to 1 for classes/structs.

This optimization makes abidw's reading be 10% faster (from ~5min:15s
to ~ 4min:45s) on a fullblow vmlinux.  Note that abidw writting time
hasn't been yet optimized.

	* src/abg-dwarf-reader.cc (die_is_class_type): Take a const
	pointer to Dwarf_Die.
	(compare_as_decl_dies): For classes/structs, call
	compare_dies_string_attribute_value just once to compare the
	DW_AT_name attribute values.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>

diff --git a/src/abg-dwarf-reader.cc b/src/abg-dwarf-reader.cc
index 6995397614c11cdea749c27edeb437c0b3615106..f8b96f46e085dbd4d461f7961bfbe1f28296138e 100644 (file)
--- a/src/abg-dwarf-reader.cc
+++ b/src/abg-dwarf-reader.cc
@@ -346,7 +346,7 @@ static bool
 die_is_pointer_reference_or_typedef_type(const Dwarf_Die* die);
 
 static bool
-die_is_class_type(Dwarf_Die* die);
+die_is_class_type(const Dwarf_Die* die);
 
 static bool
 die_is_qualified_type(const Dwarf_Die* die);
@@ -9571,9 +9571,9 @@ die_is_pointer_reference_or_typedef_type(const Dwarf_Die* die)
 ///
 /// @return true iff @p die represents a class type.
 static bool
-die_is_class_type(Dwarf_Die* die)
+die_is_class_type(const Dwarf_Die* die)
 {
-  int tag = dwarf_tag(die);
+  int tag = dwarf_tag(const_cast<Dwarf_Die*>(die));
 
   if (tag == DW_TAG_class_type || tag == DW_TAG_structure_type)
     return true;
@@ -12132,27 +12132,38 @@ compare_as_decl_dies(const Dwarf_Die *l, const Dwarf_Die *r)
 {
   ABG_ASSERT(l && r);
 
-  if (dwarf_tag(const_cast<Dwarf_Die*>(l))
-      != dwarf_tag(const_cast<Dwarf_Die*>(r)))
+  int l_tag = dwarf_tag(const_cast<Dwarf_Die*>(l));
+  int r_tag = dwarf_tag(const_cast<Dwarf_Die*>(r));
+  if (l_tag != r_tag)
     return false;
 
   bool result = false;
-  if (compare_dies_string_attribute_value(l, r, DW_AT_linkage_name,
-                                         result)
-      || compare_dies_string_attribute_value(l, r, DW_AT_MIPS_linkage_name,
-                                            result))
+
+  if (l_tag == DW_TAG_subprogram || l_tag == DW_TAG_variable)
     {
-      if (!result)
-       return false;
+      // Fast path for functions and global variables.
+      if (compare_dies_string_attribute_value(l, r, DW_AT_linkage_name,
+                                             result)
+         || compare_dies_string_attribute_value(l, r, DW_AT_MIPS_linkage_name,
+                                                result))
+       {
+         if (!result)
+           return false;
+       }
+
+      if (compare_dies_string_attribute_value(l, r, DW_AT_name,
+                                             result))
+       {
+         if (!result)
+           return false;
+       }
+      return true;
     }
 
+  // Fast path for types.
   if (compare_dies_string_attribute_value(l, r, DW_AT_name,
                                          result))
-    {
-      if (!result)
-       return false;
-    }
-
+    return result;
   return true;
 }