Here the initializer for 'x' is represented as an empty CONSTRUCTOR due to its empty element type. So during constexpr evaluation of the ARRAY_REF 'x[0]', we end up trying to lazily value initialize the omitted element at index 0, which fails because the element type is not default initializable.
This patch makes cxx_eval_array_reference handle specially the case where the element type is empty. Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for trunk? PR c++/101194 gcc/cp/ChangeLog: * constexpr.c (cxx_eval_array_reference): When the element type is empty, just return an empty CONSTRUCTOR for an omitted element instead of attempting value initialization. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/constexpr-empty16.C: New test. --- gcc/cp/constexpr.c | 4 +++- gcc/testsuite/g++.dg/cpp0x/constexpr-empty16.C | 10 ++++++++++ 2 files changed, 13 insertions(+), 1 deletion(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-empty16.C diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c index 4cd9db33a1a..39787f3f5d5 100644 --- a/gcc/cp/constexpr.c +++ b/gcc/cp/constexpr.c @@ -3845,7 +3845,9 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t, directly for non-aggregates to avoid creating a garbage CONSTRUCTOR. */ tree val; constexpr_ctx new_ctx; - if (CP_AGGREGATE_TYPE_P (elem_type)) + if (is_really_empty_class (elem_type, /*ignore_vptr*/false)) + return build_constructor (elem_type, NULL); + else if (CP_AGGREGATE_TYPE_P (elem_type)) { tree empty_ctor = build_constructor (init_list_type_node, NULL); val = digest_init (elem_type, empty_ctor, tf_warning_or_error); diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-empty16.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-empty16.C new file mode 100644 index 00000000000..79be244a1d0 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-empty16.C @@ -0,0 +1,10 @@ +// PR c++/101194 +// { dg-do compile { target c++11 } } + +struct nodefault { + constexpr nodefault(int) { } +}; + +constexpr nodefault x[1] = { nodefault{0} }; + +constexpr nodefault y = x[0]; -- 2.32.0.93.g670b81a890