Fix handling of implicit_pure by checking if non-pure procedures are called.

Procedures are marked as implicit_pure if they fulfill the criteria of
pure procedures.  In this case, a procedure was not marked as not being
implicit_pure which called another procedure, which had not yet been
marked as not being implicit_impure.

Fixed by iterating over all procedures, setting callers of procedures
which are non-pure and non-implicit_pure as non-implicit_pure and
doing this until no more procedure has been changed.

gcc/fortran/ChangeLog:

2020-07-19  Thomas Koenig  <tkoenig@gcc.gnu.org>

	PR fortran/96018
	* frontend-passes.c (gfc_check_externals): Adjust formatting.
	(implicit_pure_call): New function.
	(implicit_pure_expr): New function.
	(gfc_fix_implicit_pure): New function.
	* gfortran.h (gfc_fix_implicit_pure): New prototype.
	* parse.c (translate_all_program_units): Call gfc_fix_implicit_pure.

1 files changed, 22 insertions, 0 deletions

diff --git a/gcc/fortran/parse.c b/gcc/fortran/parse.c
index 3671513..d30208f 100644
--- a/gcc/fortran/parse.c
+++ b/gcc/fortran/parse.c
@@ -6447,6 +6447,11 @@ loop:
 
   gfc_resolve (gfc_current_ns);
 
+  /* Fix the implicit_pure attribute for those procedures who should
+     not have it.  */
+  while (gfc_fix_implicit_pure (gfc_current_ns))
+    ;
+
   /* Dump the parse tree if requested.  */
   if (flag_dump_fortran_original)
     gfc_dump_parse_tree (gfc_current_ns, stdout);
@@ -6492,6 +6497,23 @@ done:
   /* Do the resolution.  */
   resolve_all_program_units (gfc_global_ns_list);
 
+  /* Go through all top-level namespaces and unset the implicit_pure
+     attribute for any procedures that call something not pure or
+     implicit_pure.  Because the a procedure marked as not implicit_pure
+     in one sweep may be called by another routine, we repeat this
+     process until there are no more changes.  */
+  bool changed;
+  do
+    {
+      changed = false;
+      for (gfc_current_ns = gfc_global_ns_list; gfc_current_ns;
+	   gfc_current_ns = gfc_current_ns->sibling)
+	{
+	  if (gfc_fix_implicit_pure (gfc_current_ns))
+	    changed = true;
+	}
+    }
+  while (changed);
 
   /* Fixup for external procedures.  */
   for (gfc_current_ns = gfc_global_ns_list; gfc_current_ns;