Re: [PATCH] libdw: Make dwarf_getfuncs find all (defining) DW_TAG_subprogram DIEs.

[Josh Stone <jistone at redhat dot com>]

On 09/24/2013 01:53 AM, Mark Wielaard wrote:
> Hopefully with your suggestions for some improvements in the DIE
> classifying we can get rid of the last remaining "slowdown".

We can't expect to get rid of all slowdown, because it is doing more
analysis of the tree regardless.

But anyway, here's a quick patch to "unclassify" visit_scopes.  This is
good for a pretty consistent 30-40ms savings on my machine.  Nothing
earth-shattering, but it's some recouped loss.

If you approve, I can send it more formally. (w/ ChangeLog, etc.)

diff --git a/libdw/libdw_visit_scopes.c b/libdw/libdw_visit_scopes.c
index a8555ce..487375d 100644
--- a/libdw/libdw_visit_scopes.c
+++ b/libdw/libdw_visit_scopes.c
@@ -33,10 +33,9 @@
 #include "libdwP.h"
 #include <dwarf.h>
 
-enum die_class { ignore, match, match_inline, walk, imported };
 
-static enum die_class
-classify_die (Dwarf_Die *die)
+static bool
+may_have_scopes (Dwarf_Die *die)
 {
   switch (INTUSE(dwarf_tag) (die))
     {
@@ -48,31 +47,21 @@ classify_die (Dwarf_Die *die)
     case DW_TAG_catch_block:
     case DW_TAG_try_block:
     case DW_TAG_entry_point:
-      return match;
     case DW_TAG_inlined_subroutine:
-      return match_inline;
     case DW_TAG_subprogram:
-      /* This might be a concrete out-of-line instance of an inline, in
-	 which case it is not guaranteed to be owned by the right scope and
-	 we will search for its origin as for DW_TAG_inlined_subroutine.  */
-      return (INTUSE(dwarf_hasattr) (die, DW_AT_abstract_origin)
-	      ? match_inline : match);
+      return true;
 
       /* DIEs without addresses that can own DIEs with addresses.  */
     case DW_TAG_namespace:
     case DW_TAG_class_type:
     case DW_TAG_structure_type:
-      return walk;
-
-      /* Special indirection required.  */
-    case DW_TAG_imported_unit:
-      return imported;
+      return true;
 
       /* Other DIEs we have no reason to descend.  */
     default:
       break;
     }
-  return ignore;
+  return false;
 }
 
 int
@@ -104,7 +93,7 @@ __libdw_visit_scopes (depth, root, previsit, postvisit, arg)
 	   that unit are siblings of the other children.  So don't do
 	   a full recursion into the imported unit, but just walk the
 	   children in place before moving to the next real child.  */
-	while (classify_die (&child.die) == imported)
+	while (INTUSE(dwarf_tag) (&child.die) == DW_TAG_imported_unit)
 	  {
 	    Dwarf_Die orig_child_die = child.die;
 	    Dwarf_Attribute attr_mem;
@@ -134,23 +123,13 @@ __libdw_visit_scopes (depth, root, previsit, postvisit, arg)
 	      return result;
 	  }
 
-	if (!child.prune)
-	  switch (classify_die (&child.die))
-	    {
-	    case match:
-	    case match_inline:
-	    case walk:
-	      if (INTUSE(dwarf_haschildren) (&child.die))
-		{
-		  int result = recurse ();
-		  if (result != DWARF_CB_OK)
-		    return result;
-		}
-	      break;
-
-	    default:
-	      break;
-	    }
+	if (!child.prune && may_have_scopes (&child.die)
+	    && INTUSE(dwarf_haschildren) (&child.die))
+	  {
+	    int result = recurse ();
+	    if (result != DWARF_CB_OK)
+	      return result;
+	  }
 
 	if (postvisit != NULL)
 	  {