Re: [PATCH] proposed fix for bug # 61144

[Alexander Monakov <amonakov@ispras.ru>]

On Mon, 16 Jun 2014, Jan Hubicka wrote:
> > >   /* Variables declared 'const' without an initializer
> > >      have zero as the initializer if they may not be
> > >      overridden at link or run time.  */
> > >   if (!DECL_INITIAL (real_decl)
> > >       && (DECL_EXTERNAL (decl) || decl_replaceable_p (decl)))
> > >     return error_mark_node;
> > > 
> > > Honza?
> > 
> > Indeed, this may be a better place to do it as long as
> > decl_replaceable_p reliably returns true for weak aliases. If so, the
> > following might work:
> > 
> >    if ((!DECL_INITIAL (real_decl) && DECL_EXTERNAL (decl))
> >        || decl_replaceable_p (decl)))
> >      return error_mark_node;
> > 
> > On the other hand, I might just separate it out into two separate if
> > statements since they should probably have their own comments.
> 
> Yep, this looks like correct change.  I used to have FIXME on this but
> it seems it went away during some cleanups - the original condition was
> comming from expmed's folding and indeed it looked unsafe to me.
> 
> This change is OK with the testcase (if it passes testing)

I'd like to push this topic forward a bit.  I've bootstrapped and regtested a
version of the patch based on the initial proposal to check DECL_WEAK.  The
approach with decl_replaceable_p looks not that easy; I'll expand in a
followup email.

OK for trunk/branch?

2014-07-22  Rich Felker  <dalias@libc.org>
	    Alexander Monakov  <amonakov@ispras.ru>

gcc/
	PR ipa/61144
	* varpool.c (ctor_for_folding): Reject weak data.

gcc/testsuite/

	PR ipa/61144
	* gcc.dg/special/wkali-3.c: New test.
	* gcc.dg/special/wkali-3a.c: Auxiliary file.

diff --git a/gcc/varpool.c b/gcc/varpool.c
index 04ce714..9ef2195 100644
--- a/gcc/varpool.c
+++ b/gcc/varpool.c
@@ -378,6 +378,9 @@ ctor_for_folding (tree decl)
       return error_mark_node;
     }
 
+  if (DECL_WEAK (decl) && !DECL_VIRTUAL_P (decl))
+    return error_mark_node;
+
   gcc_assert (TREE_CODE (decl) == VAR_DECL);
 
   real_node = node = varpool_get_node (decl);
diff --git a/gcc/testsuite/gcc.dg/special/wkali-3.c b/gcc/testsuite/gcc.dg/special/wkali-3.c
new file mode 100644
index 0000000..407ace6
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/special/wkali-3.c
@@ -0,0 +1,17 @@
+/* { dg-do run } */
+/* { dg-require-weak "" } */
+/* { dg-require-alias "" } */
+/* { dg-additional-sources "wkali-3a.c" } */
+
+#include <stdlib.h>
+
+static const int dummy = 0;
+extern const int foo __attribute__((__weak__, __alias__("dummy")));
+
+int main(void) {
+
+    if (foo)
+        exit(0);
+    else
+        abort();
+}
diff --git a/gcc/testsuite/gcc.dg/special/wkali-3a.c b/gcc/testsuite/gcc.dg/special/wkali-3a.c
new file mode 100644
index 0000000..b3bc6a4
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/special/wkali-3a.c
@@ -0,0 +1,3 @@
+/* { dg-do run } */
+
+int foo = 1;