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From: "mscfd at gmx dot net" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/98426] find_symbol in module.c traverses O(N) part of a
 search tree
Date: Tue, 29 Dec 2020 11:15:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98426

--- Comment #3 from martin <mscfd at gmx dot net> ---
Sorry for the noise, but as this gives big reductions in compilation time i=
t 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->n=
ame.
The reason why find_symbol traverses the whole tree in the worst case is th=
at
it is ordered by gfc_symtree->name but it looks for gfc_symtree->n.sym->nam=
e.

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!=3DNULL). In this c=
ase,
the following patch should do the trick and traverse only log(N) of the tre=
e:

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 =3D strcmp (name, st->name);
+  if (c < 0)
+    retval =3D find_symbol (st->left, name, module, generic);
+  else if (c > 0)
+    retval =3D find_symbol (st->right, name, module, generic);
+  else
+    retval =3D NULL;
+
+/* original traverse
   retval =3D find_symbol (st->left, name, module, generic);

   if (retval =3D=3D NULL)
     retval =3D find_symbol (st->right, name, module, generic);
+*/

   return retval;
 }=