Re: [PATCH] PR28901 Add two levels for -Wunused-const-variable.

[Mark Wielaard <mjw at redhat dot com>]

On Tue, 2016-02-23 at 09:26 +0100, Jakub Jelinek wrote:
> On Tue, Feb 23, 2016 at 08:55:40AM +0100, Mark Wielaard wrote:
> > On Mon, 2016-02-22 at 19:20 -0800, H.J. Lu wrote:
> > > It caused:
> > > 
> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69911
> > 
> > Apologies. Apparently main_input_filename can be NULL. I am not entirely
> > sure when that happens. Or how I failed to see that test failure. I
> > think I didn't have java enabled, causing libffi to be skipped.
> > 
> > I am testing this patch that skips the test in that case:
> 
> Are you sure that is the problem?

No :) I was still bootstrapping. I did see it didn't solve the issue but
hadn't understood why yet...

> I think it doesn't hurt to check for non-NULL main_input_filename, perhaps
> some non-c-family languages might not set it, and this is in generic code,
> but at least on the gcc.target/i386/iamcu/test_passing_structs.c testcase and on one
> randomly selected libffi testcase I see the ICE from completely different
> reason - what is NULL is DECL_SOURCE_FILE (decl).

Thanks, that makes more sense than my first hypothesis.

> We are not really going to warn about this anyway, e.g. because
> it is DECL_ARTIFICIAL, but that is checked only in a much later
> condition.  So, I think you should check also for NULL DECL_SOURCE_FILE
> (and treat it as possibly in a header).  Unfortunately
> DECL_SOURCE_FILE involves a function call, so you might want to cache
> it in some automatic variable.
> 		&& (warn_unused_const_variable == 2
> 		    || (main_input_filename != NULL
> 		        && (decl_file = DECL_SOURCE_FILE (decl)) != NULL
> 			&& filename_cmp (main_input_filename,
> 					 decl_file) == 0))))

That looks right. Now testing:

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 49f6c25..e9e1aab 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2016-02-23  Mark Wielaard  <mjw@redhat.com>
+	    Jakub Jelinek  <jakub@redhat.com>
+
+	PR c/69911
+	* cgraphunit.c (check_global_declaration): Check main_input_filename
+	and DECL_SOURCE_FILE are not NULL.
+
 2016-02-20  Mark Wielaard  <mjw@redhat.com>
 
 	PR c/28901
diff --git a/gcc/cgraphunit.c b/gcc/cgraphunit.c
index 27a073a..8b3fddc 100644
--- a/gcc/cgraphunit.c
+++ b/gcc/cgraphunit.c
@@ -917,6 +917,7 @@ walk_polymorphic_call_targets (hash_set<void *> *reachable_call_targets,
 static void
 check_global_declaration (symtab_node *snode)
 {
+  const char *decl_file;
   tree decl = snode->decl;
 
   /* Warn about any function declared static but not defined.  We don't
@@ -944,8 +945,10 @@ check_global_declaration (symtab_node *snode)
        || (((warn_unused_variable && ! TREE_READONLY (decl))
 	    || (warn_unused_const_variable > 0 && TREE_READONLY (decl)
 		&& (warn_unused_const_variable == 2
-		    || filename_cmp (main_input_filename,
-				     DECL_SOURCE_FILE (decl)) == 0)))
+		    || (main_input_filename != NULL
+			&& (decl_file = DECL_SOURCE_FILE (decl)) != NULL
+			&& filename_cmp (main_input_filename,
+					 decl_file) == 0))))
 	   && TREE_CODE (decl) == VAR_DECL))
       && ! DECL_IN_SYSTEM_HEADER (decl)
       && ! snode->referred_to_p (/*include_self=*/false)