[PERF] Speedup comparing declaration-only class_decls

The structural comparison of declaration-only class_decl has show up
high on performance profiles while running abidw --abidiff on the
r300_dri.so binary.

The class_decl::get_is_declaration_only() function seems to be used
too many times.  The copying of the qualified name of the class_decl
showed up too.  Also, it looks like that the != operator on string is
slightly slower than than the == operator; OK, this is while looking
at a binary without optimizations, but still.

So the patch addresses the specific issues above.

	* src/abg-ir.cc (equals): In the overload for class_decl, avoid
	calling class_decl::get_is_declaration_only() several times.
	Avoid copying the qualified name of the class_decl.  Also, use the
	== operator to compare strings, rather than the != one.

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

diff --git a/src/abg-ir.cc b/src/abg-ir.cc
index 3d7a77a..e869780 100644 (file)
--- a/src/abg-ir.cc
+++ b/src/abg-ir.cc
@@ -11831,24 +11831,31 @@ equals(const class_decl& l, const class_decl& r, change_kind* k)
 
   // if one of the classes is declaration-only, look through it to
   // get its definition.
-  if (l.get_is_declaration_only()
-      || r.get_is_declaration_only())
+  bool l_is_decl_only = l.get_is_declaration_only();
+  bool r_is_decl_only = r.get_is_declaration_only();
+  if (l_is_decl_only || r_is_decl_only)
     {
-      const class_decl* def1 = l.get_is_declaration_only()
+      const class_decl* def1 = l_is_decl_only
        ? l.get_definition_of_declaration().get()
        : &l;
 
-      const class_decl* def2 = r.get_is_declaration_only()
+      const class_decl* def2 = r_is_decl_only
        ? r.get_definition_of_declaration().get()
        : &r;
 
-      if (!def1 || !def2
-         || def1->get_is_declaration_only()
-         || def2->get_is_declaration_only())
+      if (!def1 || !def2)
        {
-         string q1 = l.get_qualified_name();
-         string q2 = r.get_qualified_name();
-         if (q1 != q2)
+         const string& q1 = l.get_qualified_name();
+         const string& q2 = r.get_qualified_name();
+         if (q1 == q2)
+           // Not using RETURN(true) here, because that causes
+           // performance issues.  We don't need to do
+           // l.priv_->unmark_as_being_compared({l,r}) here because
+           // we haven't marked l or r as being compared yet, and
+           // doing so has a peformance cost that shows up on
+           // performance profiles for *big* libraries.
+           return true;
+         else
            {
              if (k)
                *k |= LOCAL_CHANGE_KIND;
@@ -11860,13 +11867,6 @@ equals(const class_decl& l, const class_decl& r, change_kind* k)
              // performance profiles for *big* libraries.
              return false;
            }
-         // Not using RETURN(true) here, because that causes
-         // performance issues.  We don't need to do
-         // l.priv_->unmark_as_being_compared({l,r}) here because
-         // we haven't marked l or r as being compared yet, and
-         // doing so has a peformance cost that shows up on
-         // performance profiles for *big* libraries.
-         return true;
        }
 
       if (l.priv_->comparison_started(l)