c++: cp_stabilize_reference and non-dep exprs [PR111919]

After the removal of NON_DEPENDENT_EXPR, cp_stabilize_reference (which
used to just exit early for NON_DEPENDENT_EXPR) is now more prone to
passing a weird templated tree to middle-end routines, which for the
testcase below leads to a crash from contains_placeholder_p.  It seems
the best fix is to just exit early when in a template context, like we
do in the closely related function cp_save_expr.

	PR c++/111919

gcc/cp/ChangeLog:

	* tree.cc (cp_stabilize_reference): Do nothing when
	processing_template_decl.

gcc/testsuite/ChangeLog:

	* g++.dg/template/non-dependent27.C: New test.

2 files changed, 12 insertions, 0 deletions

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index a3d61d3..417c92b 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -408,6 +408,10 @@ bitfield_p (const_tree ref)
 tree
 cp_stabilize_reference (tree ref)
 {
+  if (processing_template_decl)
+    /* As in cp_save_expr.  */
+    return ref;
+
   STRIP_ANY_LOCATION_WRAPPER (ref);
   switch (TREE_CODE (ref))
     {
diff --git a/gcc/testsuite/g++.dg/template/non-dependent27.C b/gcc/testsuite/g++.dg/template/non-dependent27.C
new file mode 100644
index 0000000..c06bca7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent27.C
@@ -0,0 +1,8 @@
+// PR c++/111919
+
+int i[42];
+
+template<class T>
+void f() {
+  i[42 / (int)sizeof(T)] |= 42;
+}