[glib] gvariant tests: workaround libc/compiler "issue"

[Ryan Lortie <desrt src gnome org>]

commit f727c820b823178285d90b3f033f7d2a4d3cdf9f
Author: Ryan Lortie <desrt desrt ca>
Date:   Tue Jun 24 10:40:30 2014 -0400

    gvariant tests: workaround libc/compiler "issue"
    
    memcmp() is declared by glibc as follows:
    
      /* Compare N bytes of S1 and S2.  */
      extern int memcmp (const void *__s1, const void *__s2, size_t __n)
           __THROW __attribute_pure__ __nonnull ((1, 2));
    
    despite the fact that it is valid to call it with a null pointer if the
    size is zero.
    
    gcc 4.9.0 contains a new optimisation that sees that we pass a pointer
    to this function and concludes that it certainly must not be null,
    removing a later check and thereby causing a crash.
    
    We protect the invocation of memcmp() with a condition to prevent gcc
    from making this false assumption (arguably under wrong advice from
    glibc).

 glib/tests/gvariant.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)
---
diff --git a/glib/tests/gvariant.c b/glib/tests/gvariant.c
index 122400e..9152a43 100644
--- a/glib/tests/gvariant.c
+++ b/glib/tests/gvariant.c
@@ -1520,7 +1520,9 @@ test_array (void)
         g_variant_serialiser_serialise (serialised, random_instance_filler,
                                         (gpointer *) instances, n_children);
 
-        g_assert (memcmp (serialised.data, data, serialised.size) == 0);
+        if (serialised.size)
+          g_assert (memcmp (serialised.data, data, serialised.size) == 0);
+
         g_assert (g_variant_serialised_n_children (serialised) == n_children);
 
         for (i = 0; i < n_children; i++)
@@ -1681,7 +1683,9 @@ test_tuple (void)
         g_variant_serialiser_serialise (serialised, random_instance_filler,
                                         (gpointer *) instances, n_children);
 
-        g_assert (memcmp (serialised.data, data, serialised.size) == 0);
+        if (serialised.size)
+          g_assert (memcmp (serialised.data, data, serialised.size) == 0);
+
         g_assert (g_variant_serialised_n_children (serialised) == n_children);
 
         for (i = 0; i < n_children; i++)
@@ -1774,7 +1778,9 @@ test_variant (void)
         g_variant_serialiser_serialise (serialised, random_instance_filler,
                                         (gpointer *) &instance, 1);
 
-        g_assert (memcmp (serialised.data, data, serialised.size) == 0);
+        if (serialised.size)
+          g_assert (memcmp (serialised.data, data, serialised.size) == 0);
+
         g_assert (g_variant_serialised_n_children (serialised) == 1);
 
         child = g_variant_serialised_get_child (serialised, 0);