[Patch, Fortran] PR50923 - [4.4-4.7] Print warning function does not return a value

[Tobias Burnus <burnus at net-b dot de>]

The bug has been introduced when changing the warning system to do more 
in the front end. The problem is that for:
  module m
  contains
    function f()
    end
  end
the sym->attr.referenced gets set - and no warning is printed. I now 
ignore the sym->attr.referenced attribute as the RESULT == NULL_TREE 
should only be reached if the variable has not been assigned a value.

Additionally, I now only set TREE_NO_WARNING() if a warning has been 
printed; that way, some other useful middle-end warnings might be still 
printed. I have to set the NO_WARNING also for sym != sym->result as it 
otherwise prints a middle end warning into addition to the FE warning. 
But the FE warning has been printed already before for the result variable.

Build and regtested on x86-64-linux.
OK for the trunk? How far should this be backported - all the way down 
to 4.4?

Tobias
2011-11-30  Tobias Burnus  <burnus@net-b.de>

	PR fortran/50923
	* trans-decl.c (generate_local_decl): Set TREE_NO_WARNING only
	if the front end has printed a warning.
	(gfc_generate_function_code): Fix unset-result warning.

2011-11-30  Tobias Burnus  <burnus@net-b.de>

	PR fortran/50923
	* gfortran.dg/warn_function_without_result_2.f90: New.


diff --git a/gcc/fortran/trans-decl.c b/gcc/fortran/trans-decl.c
index 67bd3e2..b8789a4 100644
--- a/gcc/fortran/trans-decl.c
+++ b/gcc/fortran/trans-decl.c
@@ -4510,10 +4532,16 @@ generate_local_decl (gfc_symbol * sym)
 			     "declared INTENT(OUT) but was not set and "
 			     "does not have a default initializer",
 			     sym->name, &sym->declared_at);
+	      if (sym->backend_decl != NULL_TREE)
+		TREE_NO_WARNING(sym->backend_decl) = 1;
 	    }
 	  else if (gfc_option.warn_unused_dummy_argument)
-	    gfc_warning ("Unused dummy argument '%s' at %L", sym->name,
+	    {
+	      gfc_warning ("Unused dummy argument '%s' at %L", sym->name,
 			 &sym->declared_at);
+	      if (sym->backend_decl != NULL_TREE)
+		TREE_NO_WARNING(sym->backend_decl) = 1;
+	    }
 	}
 
       /* Warn for unused variables, but not if they're inside a common
@@ -4521,11 +4549,19 @@ generate_local_decl (gfc_symbol * sym)
       else if (warn_unused_variable
 	       && !(sym->attr.in_common || sym->attr.use_assoc || sym->mark
 		    || sym->attr.in_namelist))
-	gfc_warning ("Unused variable '%s' declared at %L", sym->name,
-		     &sym->declared_at);
+	{
+	  gfc_warning ("Unused variable '%s' declared at %L", sym->name,
+		       &sym->declared_at);
+	  if (sym->backend_decl != NULL_TREE)
+	    TREE_NO_WARNING(sym->backend_decl) = 1;
+	}
       else if (warn_unused_variable && sym->attr.use_only)
-	gfc_warning ("Unused module variable '%s' which has been explicitly "
-		     "imported at %L", sym->name, &sym->declared_at);
+	{
+	  gfc_warning ("Unused module variable '%s' which has been explicitly "
+		       "imported at %L", sym->name, &sym->declared_at);
+	  if (sym->backend_decl != NULL_TREE)
+	    TREE_NO_WARNING(sym->backend_decl) = 1;
+	}
 
       /* For variable length CHARACTER parameters, the PARM_DECL already
 	 references the length variable, so force gfc_get_symbol_decl
@@ -4561,11 +4597,6 @@ generate_local_decl (gfc_symbol * sym)
 	mark the symbol now, as well as in traverse_ns, to prevent
 	getting stuck in a circular dependency.  */
       sym->mark = 1;
-
-      /* We do not want the middle-end to warn about unused parameters
-         as this was already done above.  */
-      if (sym->attr.dummy && sym->backend_decl != NULL_TREE)
-	  TREE_NO_WARNING(sym->backend_decl) = 1;
     }
   else if (sym->attr.flavor == FL_PARAMETER)
     {
@@ -5288,11 +5315,11 @@ gfc_generate_function_code (gfc_namespace * ns)
       if (result == NULL_TREE)
 	{
 	  /* TODO: move to the appropriate place in resolve.c.  */
-	  if (warn_return_type && !sym->attr.referenced && sym == sym->result)
+	  if (warn_return_type && sym == sym->result)
 	    gfc_warning ("Return value of function '%s' at %L not set",
 			 sym->name, &sym->declared_at);
-
-	  TREE_NO_WARNING(sym->backend_decl) = 1;
+	  if (warn_return_type)
+	    TREE_NO_WARNING(sym->backend_decl) = 1;
 	}
       else
 	gfc_add_expr_to_block (&body, gfc_generate_return ());
--- /dev/null	2011-11-29 07:50:43.475522632 +0100
+++ gcc/gcc/testsuite/gfortran.dg/warn_function_without_result_2.f90	2011-11-30 17:52:38.000000000 +0100
@@ -0,0 +1,19 @@
+! { dg-do compile }
+! { dg-options "-Wall" }
+!
+! PR fortran/50923
+!
+module m
+contains
+  integer pure function f() ! { dg-warning "Return value of function 'f' at .1. not set" }
+  end function f
+  integer pure function g() result(h) ! { dg-warning "Return value 'h' of function 'g' declared at .1. not set" }
+  end function g
+  integer pure function i()
+    i = 7
+  end function i
+  integer pure function j() result(k)
+    k = 8
+  end function j
+end module m
+! { dg-final { cleanup-modules "mod" } }