c++: mutable temps in rodata

If the type of a temporary has mutable members, we can't set TREE_READONLY
on the VAR_DECL; this is parallel to the check in
cp_apply_type_quals_to_decl.

gcc/cp/ChangeLog:

	* tree.cc (build_target_expr): Check TYPE_HAS_MUTABLE_P.

gcc/testsuite/ChangeLog:

	* g++.dg/tree-ssa/initlist-opt6.C: New test.

2 files changed, 19 insertions, 0 deletions

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 751c9ad..799183d 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -522,6 +522,7 @@ build_target_expr (tree decl, tree value, tsubst_flags_t complain)
   if (CP_TYPE_CONST_NON_VOLATILE_P (type)
       && !TYPE_HAS_NONTRIVIAL_DESTRUCTOR (type)
       && !VOID_TYPE_P (TREE_TYPE (value))
+      && !TYPE_HAS_MUTABLE_P (type)
       && reduced_constant_expression_p (value))
     TREE_READONLY (decl) = true;
 
diff --git a/gcc/testsuite/g++.dg/tree-ssa/initlist-opt6.C b/gcc/testsuite/g++.dg/tree-ssa/initlist-opt6.C
new file mode 100644
index 0000000..ea1bf5d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/initlist-opt6.C
@@ -0,0 +1,18 @@
+// { dg-do compile { target c++11 } }
+// { dg-additional-options -fdump-tree-gimple }
+// { dg-final { scan-tree-dump-not {static const struct S} "gimple" } }
+
+// Test that mutable prevents putting this init-list array in rodata.
+
+#include <initializer_list>
+
+struct S {
+    constexpr S(int i) : i(i) {}
+    mutable int i;
+};
+
+void f(std::initializer_list<S>);
+
+int main() {
+    f({1,2,3});
+}