[PATCH v1] cxx: Make __func__, __FUNCTION__, and __PRETTY_FUNCTION__ constexpr.

[Franklin “Snaipe” Mathieu]

From: Franklin “Snaipe” Mathieu <sna...@diacritic.io>

This patch makes the forementioned definitions `contexpr` when
compiling C++11 and above with GNU extensions.

gcc/cp/ChangeLog:
2017-06-27  Franklin “Snaipe” Mathieu  <sna...@diacritic.io>

        PR c++/66639
        * decl.c (cp_make_fname_decl): Make declaration constexpr.

gcc/testsuite/ChangeLog:
2017-06-27  Franklin “Snaipe” Mathieu  <sna...@diacritic.io>

        PR c++/66639
        * g++.dg/pr66639.c: New test.
---
 gcc/cp/decl.c                  |  5 +++++
 gcc/testsuite/g++.dg/pr66639.C | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/pr66639.C

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 8e9a466..740ab71 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -4384,6 +4384,11 @@ cp_make_fname_decl (location_t loc, tree id, int 
type_dep)
   TREE_READONLY (decl) = 1;
   DECL_ARTIFICIAL (decl) = 1;
 
+  /* extension: declare __func__, __FUNCTION__, and __PRETTY_FUNCTION__ as
+     constexpr.  */
+  if (!flag_iso && cxx_dialect >= cxx11)
+    DECL_DECLARED_CONSTEXPR_P (decl) = 1;
+
   TREE_USED (decl) = 1;
 
   if (current_function_decl)
diff --git a/gcc/testsuite/g++.dg/pr66639.C b/gcc/testsuite/g++.dg/pr66639.C
new file mode 100644
index 0000000..51a92f9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr66639.C
@@ -0,0 +1,19 @@
+// PR c++/66639
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+constexpr bool
+streq(char const *lhs, char const *rhs)
+{
+  return *lhs && *rhs
+     ? *lhs == *rhs && streq(lhs + 1, rhs + 1)
+     : !*lhs && !*rhs;
+}
+
+int
+main()
+{
+   static_assert (streq(__func__, "main"), "");
+   static_assert (streq(__FUNCTION__, "main"), "");
+   static_assert (streq(__PRETTY_FUNCTION__, "int main()"), "");
+}
-- 
Franklin "Snaipe" Mathieu
Arista Networks, Ltd