https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70590
--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #8)
> --- a/gcc/cp/constexpr.c
> +++ b/gcc/cp/constexpr.c
> @@ -4143,6 +4143,12 @@ cxx_eval_outermost_constant_expr (tree t, bool
> allow_non_constant,
>
> verify_constant (r, allow_non_constant, &non_constant_p, &overflow_p);
>
> + /* Unshare the result unless it's a CONSTRUCTOR in which case it's already
> + unshared. */
> + if (r != t
> + && TREE_CODE (r) != CONSTRUCTOR)
> + r = unshare_expr (r);
> +
> /* Mutable logic is a bit tricky: we want to allow initialization of
> constexpr variables with mutable members, but we can't copy those
> members to another constexpr variable. */
Wouldn't it be better to move it even further down, so that we don't unshare
even when actually not returning r or something based on it?
E.g. (completely untested)?
--- gcc/cp/constexpr.c.jj 2016-04-07 23:27:44.000000000 +0200
+++ gcc/cp/constexpr.c 2016-04-08 17:36:49.774326934 +0200
@@ -4168,6 +4168,11 @@ cxx_eval_outermost_constant_expr (tree t
return error_mark_node;
else if (non_constant_p && TREE_CONSTANT (r))
{
+ /* Unshare the result unless it's a CONSTRUCTOR in which case it's
+ already unshared. */
+ if (r != t && TREE_CODE (r) != CONSTRUCTOR)
+ r = unshare_expr (r);
+
/* This isn't actually constant, so unset TREE_CONSTANT. */
if (EXPR_P (r))
r = copy_node (r);
@@ -4179,6 +4184,10 @@ cxx_eval_outermost_constant_expr (tree t
}
else if (non_constant_p || r == t)
return t;
+ /* Unshare the result unless it's a CONSTRUCTOR in which case it's
+ already unshared. */
+ else if (r != t && TREE_CODE (r) != CONSTRUCTOR)
+ r = unshare_expr (r);
if (TREE_CODE (r) == CONSTRUCTOR && CLASS_TYPE_P (TREE_TYPE (r)))
{
