[Bug fortran/98426] find_symbol in module.c traverses O(N) part of a search tree

["mscfd at gmx dot net" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98426

--- Comment #3 from martin <mscfd at gmx dot net> ---
Sorry for the noise, but as this gives big reductions in compilation time it is
quite important to me (and probably other big module based projects).

I just realised that I mixed up gfc_symtree->name and gfc_symtree->n.sym->name.
The reason why find_symbol traverses the whole tree in the worst case is that
it is ordered by gfc_symtree->name but it looks for gfc_symtree->n.sym->name.

So far I got the impression that either gfc_symtree->name is a unique name
("@xxx") or equal to gfc_symtree->n.sym->name (if n.sym!=NULL). In this case,
the following patch should do the trick and traverse only log(N) of the tree:

diff --git a/gcc/fortran/module.c b/gcc/fortran/module.c
index 4c6ff22d5c1..8dc59e25d46 100644
--- a/gcc/fortran/module.c
+++ b/gcc/fortran/module.c
@@ -4659,10 +4659,20 @@ find_symbol (gfc_symtree *st, const char *name,
        return st;
     }

+  c = strcmp (name, st->name);
+  if (c < 0)
+    retval = find_symbol (st->left, name, module, generic);
+  else if (c > 0)
+    retval = find_symbol (st->right, name, module, generic);
+  else
+    retval = NULL;
+
+/* original traverse
   retval = find_symbol (st->left, name, module, generic);

   if (retval == NULL)
     retval = find_symbol (st->right, name, module, generic);
+*/

   return retval;
 }