fortran: Remove redundant tree walk to delete element

Remove preliminary walk of the symbol tree when we are about to remove an
element.  This preliminary walk was necessary because the deletion function
updated the tree without reporting back to the caller the element it had
removed.  But knowing that element is necessary to free its memory, so one
had to first get that element before it was removed from the tree.

This change updates the main deletion function delete_treap and its public
wrapper gfc_delete_bbt so that the removed element can be known by the
caller.  This makes the preliminary walk in gfc_delete_symtree redundant,
permitting its removal.

gcc/fortran/ChangeLog:

	* bbt.cc (delete_treap): Add argument REMOVED, set it to the removed
	element from the tree.  Change NULL to nullptr.
	(gfc_delete_bbt): Return the removed element from the tree.
	* gfortran.h (gfc_delete_symtree): Remove prototype.
	(gfc_delete_bbt): Set return type to pointer.
	* symbol.cc (gfc_delete_symtree): Make static.  Get the element to be
	freed from the result of gfc_delete_bbt.  Remove the preliminary walk to
	get it.

3 files changed, 32 insertions, 18 deletions

diff --git a/gcc/fortran/bbt.cc b/gcc/fortran/bbt.cc
index 851e5e9..7f1f406 100644
--- a/gcc/fortran/bbt.cc
+++ b/gcc/fortran/bbt.cc
@@ -162,37 +162,54 @@ delete_root (gfc_bbt *t)
 }
 
 
-/* Delete an element from a tree.  The 'old' value does not
-   necessarily have to point to the element to be deleted, it must
-   just point to a treap structure with the key to be deleted.
-   Returns the new root node of the tree.  */
+/* Delete an element from a tree, returning the new root node of the tree.
+   The OLD value does not necessarily have to point to the element to be
+   deleted, it must just point to a treap structure with the key to be deleted.
+   The REMOVED argument, if non-null, is set to the removed element from the
+   tree upon return.  */
 
 static gfc_bbt *
-delete_treap (gfc_bbt *old, gfc_bbt *t, compare_fn compare)
+delete_treap (gfc_bbt *old, gfc_bbt *t, compare_fn compare, gfc_bbt **removed)
 {
   int c;
 
-  if (t == NULL)
-    return NULL;
+  if (t == nullptr)
+    {
+      if (removed)
+	*removed = nullptr;
+      return nullptr;
+    }
 
   c = (*compare) (old, t);
 
   if (c < 0)
-    t->left = delete_treap (old, t->left, compare);
+    t->left = delete_treap (old, t->left, compare, removed);
   if (c > 0)
-    t->right = delete_treap (old, t->right, compare);
+    t->right = delete_treap (old, t->right, compare, removed);
   if (c == 0)
-    t = delete_root (t);
+    {
+      if (removed)
+	*removed = t;
+      t = delete_root (t);
+    }
 
   return t;
 }
 
 
-void
+/* Delete the element from the tree at *ROOT that matches the OLD element
+   according to the COMPARE_FN function.  This updates the *ROOT pointer to
+   point to the new tree root (if different from the original) and returns the
+   deleted element.  */
+
+void *
 gfc_delete_bbt (void *root, void *old, compare_fn compare)
 {
   gfc_bbt **t;
+  gfc_bbt *removed;
 
   t = (gfc_bbt **) root;
-  *t = delete_treap ((gfc_bbt *) old, *t, compare);
+  *t = delete_treap ((gfc_bbt *) old, *t, compare, &removed);
+
+  return (void *) removed;
 }
diff --git a/gcc/fortran/gfortran.h b/gcc/fortran/gfortran.h
index b37c6bb..371f874 100644
--- a/gcc/fortran/gfortran.h
+++ b/gcc/fortran/gfortran.h
@@ -3510,7 +3510,6 @@ bool gfc_reference_st_label (gfc_st_label *, gfc_sl_type);
 gfc_namespace *gfc_get_namespace (gfc_namespace *, int);
 gfc_symtree *gfc_new_symtree (gfc_symtree **, const char *);
 gfc_symtree *gfc_find_symtree (gfc_symtree *, const char *);
-void gfc_delete_symtree (gfc_symtree **, const char *);
 gfc_symtree *gfc_get_unique_symtree (gfc_namespace *);
 gfc_user_op *gfc_get_uop (const char *);
 gfc_user_op *gfc_find_uop (const char *, gfc_namespace *);
@@ -3911,7 +3910,7 @@ bool gfc_inline_intrinsic_function_p (gfc_expr *);
 /* bbt.cc */
 typedef int (*compare_fn) (void *, void *);
 void gfc_insert_bbt (void *, void *, compare_fn);
-void gfc_delete_bbt (void *, void *, compare_fn);
+void * gfc_delete_bbt (void *, void *, compare_fn);
 
 /* dump-parse-tree.cc */
 void gfc_dump_parse_tree (gfc_namespace *, FILE *);
diff --git a/gcc/fortran/symbol.cc b/gcc/fortran/symbol.cc
index aa3cdc9..2cba2ea 100644
--- a/gcc/fortran/symbol.cc
+++ b/gcc/fortran/symbol.cc
@@ -2948,7 +2948,7 @@ gfc_new_symtree (gfc_symtree **root, const char *name)
 
 /* Delete a symbol from the tree.  Does not free the symbol itself!  */
 
-void
+static void
 gfc_delete_symtree (gfc_symtree **root, const char *name)
 {
   gfc_symtree st, *st0;
@@ -2963,10 +2963,8 @@ gfc_delete_symtree (gfc_symtree **root, const char *name)
   else
     p = name;
 
-  st0 = gfc_find_symtree (*root, p);
-
   st.name = gfc_get_string ("%s", p);
-  gfc_delete_bbt (root, &st, compare_symtree);
+  st0 = (gfc_symtree *) gfc_delete_bbt (root, &st, compare_symtree);
 
   free (st0);
 }