[PATCH] c++: unpropagated CONSTRUCTOR_MUTABLE_POISON [PR110463]

[Patrick Palka <ppalka@redhat.com>]

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/13?

-- >8 --

cp_fold is neglecting to propagate CONSTRUCTOR_MUTABLE_POISON when folding
a CONSTRUCTOR initializer, which for the below testcase causes us to fail
to reject a mutable member access of a constexpr variable during constexpr
evaluation.

	PR c++/110463

gcc/cp/ChangeLog:

	* cp-gimplify.cc (cp_fold) <case CONSTRUCTOR>: Propagate
	CONSTRUCTOR_MUTABLE_POISON.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-mutable6.C: New test.
---
 gcc/cp/cp-gimplify.cc                          |  2 ++
 .../g++.dg/cpp0x/constexpr-mutable6.C          | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-mutable6.C

diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index 853b1e44236..f5734197774 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -3079,6 +3079,8 @@ cp_fold (tree x, fold_flags_t flags)
 	    x = build_constructor (TREE_TYPE (x), nelts);
 	    CONSTRUCTOR_PLACEHOLDER_BOUNDARY (x)
 	      = CONSTRUCTOR_PLACEHOLDER_BOUNDARY (org_x);
+	    CONSTRUCTOR_MUTABLE_POISON (x)
+	      = CONSTRUCTOR_MUTABLE_POISON (org_x);
 	  }
 	if (VECTOR_TYPE_P (TREE_TYPE (x)))
 	  x = fold (x);
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-mutable6.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-mutable6.C
new file mode 100644
index 00000000000..2c946e388ab
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-mutable6.C
@@ -0,0 +1,18 @@
+// PR c++/110463
+// { dg-do compile { target c++11 } }
+
+struct U {
+  mutable int x = 1;
+};
+
+struct V {
+  mutable int y = 1+1;
+};
+
+int main() {
+  constexpr U u = {};
+  constexpr int x = u.x; // { dg-error "mutable" }
+
+  constexpr V v = {};
+  constexpr int y = v.y; // { dg-error "mutable" }
+}
-- 
2.41.0.199.ga9e066fa63