On Thu, 8 Oct 2020, Patrick Palka wrote:
> In the testcase below, we're ICEing during constexpr evaluation of the
> CONSTRUCTOR {.data={{}, [1 ... 7]={}}} of type 'vector'. The apparently
> unique thing about this CONSTRUCTOR is that it has a RANGE_EXPR index
> whose corresponding sub-aggregate initializer doesn't satisfy
> reduced_constant_expression_p (because its field 't' is uninitialized).
>
> This is a problem because init_subob_ctx currently punts if the
> constructor index is a RANGE_EXPR, so when cxx_eval_bare_aggregate
> recurses into this sub-aggregate initializer we trip over the
> same_type_p assert in verify_ctor_sanity.
>
> Fix this by making init_subob_ctx set up an appropriate sub-aggregate
> initialization context even when the index is a RANGE_EXPR.
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk and the 10 branch?
>
> gcc/cp/ChangeLog:
>
> PR c++/97328
> * constexpr.c (init_subob_ctx): Don't punt if the index is a
> RANGE_EXPR, instead build a sub-aggregate initialization context
> with no subobject.
>
> gcc/testsuite/ChangeLog:
>
> PR c++/97328
> * g++.dg/cpp2a/constexpr-init19.C: New test.
> * g++.dg/cpp2a/constexpr-init20.C: New test.
Ping.
> ---
> gcc/cp/constexpr.c | 13 +++++++------
> gcc/testsuite/g++.dg/cpp2a/constexpr-init19.C | 15 +++++++++++++++
> gcc/testsuite/g++.dg/cpp2a/constexpr-init20.C | 15 +++++++++++++++
> 3 files changed, 37 insertions(+), 6 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-init19.C
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/constexpr-init20.C
>
> diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
> index a118f8a810b..e50a2a220cb 100644
> --- a/gcc/cp/constexpr.c
> +++ b/gcc/cp/constexpr.c
> @@ -3953,11 +3953,6 @@ init_subob_ctx (const constexpr_ctx *ctx,
> constexpr_ctx &new_ctx,
> {
> new_ctx = *ctx;
>
> - if (index && TREE_CODE (index) != INTEGER_CST
> - && TREE_CODE (index) != FIELD_DECL)
> - /* This won't have an element in the new CONSTRUCTOR. */
> - return;
> -
> tree type = initialized_type (value);
> if (!AGGREGATE_TYPE_P (type) && !VECTOR_TYPE_P (type))
> /* A non-aggregate member doesn't get its own CONSTRUCTOR. */
> @@ -3967,7 +3962,13 @@ init_subob_ctx (const constexpr_ctx *ctx,
> constexpr_ctx &new_ctx,
> update object to refer to the subobject and ctor to refer to
> the (newly created) sub-initializer. */
> if (ctx->object)
> - new_ctx.object = build_ctor_subob_ref (index, type, ctx->object);
> + {
> + if (index == NULL_TREE || TREE_CODE (index) == RANGE_EXPR)
> + /* There's no well-defined subobject for this index. */
> + new_ctx.object = NULL_TREE;
> + else
> + new_ctx.object = build_ctor_subob_ref (index, type, ctx->object);
> + }
> tree elt = build_constructor (type, NULL);
> CONSTRUCTOR_NO_CLEARING (elt) = true;
> new_ctx.ctor = elt;
> diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-init19.C
> b/gcc/testsuite/g++.dg/cpp2a/constexpr-init19.C
> new file mode 100644
> index 00000000000..d354c5ad609
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-init19.C
> @@ -0,0 +1,15 @@
> +// PR c++/97328
> +// { dg-do compile { target c++20 } }
> +
> +struct vector {
> + struct storage {
> + int t;
> + constexpr storage() {}
> + } data[8];
> +};
> +
> +constexpr auto foo() {
> + vector i;
> + return i;
> +}
> +auto val = foo();
> diff --git a/gcc/testsuite/g++.dg/cpp2a/constexpr-init20.C
> b/gcc/testsuite/g++.dg/cpp2a/constexpr-init20.C
> new file mode 100644
> index 00000000000..1a6ed8d86dd
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/constexpr-init20.C
> @@ -0,0 +1,15 @@
> +// PR c++/97328
> +// { dg-do compile { target c++20 } }
> +
> +struct vector {
> + union storage {
> + int t;
> + constexpr storage() {}
> + } data[8];
> +};
> +
> +constexpr auto foo() {
> + vector i;
> + return i;
> +}
> +auto val = foo();
> --
> 2.29.0.rc0
>
>
