The constexpr on the A constructor led us to try to expand the call in
the B constructor to a constant. But in that call we're passing the B
parameter s, which is not constant, so it should just fail quietly. But
instead we were trying to treat it as a STRING_CST, which causes an ICE
with checking enabled, or wrong code with checking off.
Tested x86_64-pc-linux-gnu, applying to trunk and 4.6. On the 4.6
branch I replaced the gcc_unreachable with just returning t to be extra
conservative.
commit 15dfe0b93a072a167d7a818799487119f516231d
Author: Jason Merrill <ja...@redhat.com>
Date: Fri Aug 5 16:12:24 2011 -0400
PR c++/49988
* semantics.c (cxx_eval_array_reference): Handle failure to
reduce the array operand to something we can work with.
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index ac24b77..2f02e69 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -6428,12 +6428,19 @@ cxx_eval_array_reference (const constexpr_call *call, tree t,
elem_type = TREE_TYPE (TREE_TYPE (ary));
if (TREE_CODE (ary) == CONSTRUCTOR)
len = CONSTRUCTOR_NELTS (ary);
- else
+ else if (TREE_CODE (ary) == STRING_CST)
{
elem_nchars = (TYPE_PRECISION (elem_type)
/ TYPE_PRECISION (char_type_node));
len = (unsigned) TREE_STRING_LENGTH (ary) / elem_nchars;
}
+ else
+ {
+ /* We can't do anything with other tree codes, so use
+ VERIFY_CONSTANT to complain and fail. */
+ VERIFY_CONSTANT (ary);
+ gcc_unreachable ();
+ }
if (compare_tree_int (index, len) >= 0)
{
if (tree_int_cst_lt (index, array_type_nelts_top (TREE_TYPE (ary))))
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-non-const-arg3.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-non-const-arg3.C
new file mode 100644
index 0000000..581be6d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-non-const-arg3.C
@@ -0,0 +1,23 @@
+// PR c++/49988
+// { dg-options -std=c++0x }
+// { dg-do run }
+
+template<int ... I> struct X { };
+
+struct A {
+ char data[3];
+ template<int ... I>
+ constexpr
+ A(const char (&s)[3], X<I...> x) : data{ s[I]...} { }
+};
+struct B {
+ A a;
+ B(const char (&s)[3]) : a{s,X<0,1,2>{}} { }
+};
+
+int main()
+{
+ B b{"12"};
+ if (b.a.data[0] != '1')
+ return 1;
+}