[PATCH][C++] Fix PR53605

[Richard Guenther]

When I changed empty arrays domain to use a signed sizetype [0, -1]
domain mangling of a empty-array-type broke because mangling adds
an unsigned one to the signed -1 which causes an ICE (I chose to
do that instead of shifting the range to [1, 0] because much more
code relies on a zero lower bound ...).

The following fixes that by using double-ints for the arithmetic
and thus also does not generate a not needed tree node.

Bootstrapped and tested on x86_64-unknown-linux-gnu, ok?

Thanks,
Richard.

2012-06-11  Richard Guenther  <rguent...@suse.de>

        PR c++/53616
        * mangle.c (write_array_type): Use double-ints for array domain
        arithmetic.

        * g++.dg/ext/pr53605.C: New testcase.

Index: gcc/cp/mangle.c
===================================================================
--- gcc/cp/mangle.c     (revision 188384)
+++ gcc/cp/mangle.c     (working copy)
@@ -3119,8 +3119,10 @@ write_array_type (const tree type)
        {
          /* The ABI specifies that we should mangle the number of
             elements in the array, not the largest allowed index.  */
-         max = size_binop (PLUS_EXPR, max, size_one_node);
-         write_unsigned_number (tree_low_cst (max, 1));
+         double_int dmax
+           = double_int_add (tree_to_double_int (max), double_int_one);
+         gcc_assert (double_int_fits_in_uhwi_p (dmax));
+         write_unsigned_number (dmax.low);
        }
       else
        {
Index: gcc/testsuite/g++.dg/ext/pr53605.C
===================================================================
--- gcc/testsuite/g++.dg/ext/pr53605.C  (revision 0)
+++ gcc/testsuite/g++.dg/ext/pr53605.C  (revision 0)
@@ -0,0 +1,16 @@
+// { dg-do compile }
+
+// Avoid -pedantic-error default
+// { dg-options "" }
+
+template <bool lhs_is_null_literal>
+class EqHelper {
+public:
+    template <typename T1, typename T2>
+       static int  Compare( const T1& expected,
+                            const T2& actual);
+};
+void foo(){
+    static const int kData[] = {};
+    ::EqHelper<false>::Compare(kData, "abc");
+}