C++ PATCH for c++/70709 (hang with zero-length array member)

[Jason Merrill]

Since a zero-length array is represented with a TYPE_MAX_VALUE of
unsigned -1, iterating up from 0 takes a long time.  So let's avoid
that.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit 237edb92e3aa09ad1eae62ed633bf161a8590bd7
Author: Jason Merrill <ja...@redhat.com>
Date:   Fri Jul 22 17:00:06 2016 -0400

        PR c++/70709 - zero-length array member
    
        * class.c (walk_subobject_offsets): Handle 0-length array.

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index b2db7f8..b537b7e 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -4175,7 +4175,8 @@ walk_subobject_offsets (tree type,
       /* Avoid recursing into objects that are not interesting.  */
       if (!CLASS_TYPE_P (element_type)
          || !CLASSTYPE_CONTAINS_EMPTY_CLASS_P (element_type)
-         || !domain)
+         || !domain
+         || integer_minus_onep (TYPE_MAX_VALUE (domain)))
        return 0;
 
       /* Step through each of the elements in the array.  */
diff --git a/gcc/testsuite/g++.dg/ext/array3.C 
b/gcc/testsuite/g++.dg/ext/array3.C
new file mode 100644
index 0000000..e8940db
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/array3.C
@@ -0,0 +1,19 @@
+// PR c++/70709
+// { dg-options "" }
+
+struct A
+{
+  A (int);
+};
+
+struct B
+{
+  B () {} 
+  A a[0];
+};
+
+struct C
+{
+  C () {} 
+  B a[0];
+};