Normally when we see a call to a function with a reference parameter,
we've converted the argument to have reference type as well, so we can
always treat arguments as rvalues in potential_constant_expression. But
with templates we defer the conversions until instantiation time, so we
shouldn't require the argument to be an rvalue constant yet.
Tested x86_64-pc-linux-gnu, applying to trunk.
commit dbb548c7d0adf94504c732f92120c78186834e1b
Author: Jason Merrill <ja...@redhat.com>
Date: Wed Jan 14 19:34:04 2015 -0500
PR c++/63283
* constexpr.c (potential_constant_expression_1): Handle reference
args in templates.
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 1432506..e27a892 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -3881,7 +3881,11 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict,
for (; i < nargs; ++i)
{
tree x = get_nth_callarg (t, i);
- if (!RECUR (x, rval))
+ /* In a template, reference arguments haven't been converted to
+ REFERENCE_TYPE and we might not even know if the parameter
+ is a reference, so accept lvalue constants too. */
+ bool rv = processing_template_decl ? any : rval;
+ if (!RECUR (x, rv))
return false;
}
return true;
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-template8.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-template8.C
new file mode 100644
index 0000000..7b2b9c7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-template8.C
@@ -0,0 +1,10 @@
+// PR c++/63283
+// { dg-do compile { target c++11 } }
+
+constexpr int array_length(int (&array)[3]) { return 3; }
+int a[] = { 1, 2, 3 };
+template <typename T> int f() {
+ struct { int e[array_length(a)]; } t;
+ return sizeof(t);
+}
+int main() { f<void>(); }
diff --git a/gcc/testsuite/g++.dg/cpp0x/static_assert10.C b/gcc/testsuite/g++.dg/cpp0x/static_assert10.C
index 216f259..e7f728e 100644
--- a/gcc/testsuite/g++.dg/cpp0x/static_assert10.C
+++ b/gcc/testsuite/g++.dg/cpp0x/static_assert10.C
@@ -4,5 +4,5 @@
template<typename T> bool foo(T)
{
int i;
- static_assert(foo(i), "Error"); // { dg-error "non-constant condition|not usable" }
+ static_assert(foo(i), "Error"); // { dg-error "non-constant condition|not usable|non-constexpr" }
}