On Mon, 18 Sep 2023, Patrick Palka wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
>
> -- >8 --
>
> Here convert_to_void always completes the type of an indirection or
> id-expression, but according to [expr.context] an lvalue-to-rvalue
> conversion is applied to a discarded-value expression only if "the
> expression is a glvalue of volatile-qualified type". This patch
> restricts convert_to_void's type completion to match.
>
> PR c++/111419
>
> gcc/cp/ChangeLog:
>
> * cvt.cc (convert_to_void) <case INDIRECT_REF>: Only call
> complete_type if the type is volatile.
> <case VAR_DECL>: Only call complete_type if the type is volatile.
> Likewise.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp2a/concepts-requires36.C: New test.
> * g++.dg/expr/discarded1.C: New test.
> * g++.dg/expr/discarded1a.C: New test.
> ---
> gcc/cp/cvt.cc | 10 ++++++----
> .../g++.dg/cpp2a/concepts-requires36.C | 16 ++++++++++++++++
> gcc/testsuite/g++.dg/expr/discarded1.C | 15 +++++++++++++++
> gcc/testsuite/g++.dg/expr/discarded1a.C | 17 +++++++++++++++++
> 4 files changed, 54 insertions(+), 4 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires36.C
> create mode 100644 gcc/testsuite/g++.dg/expr/discarded1.C
> create mode 100644 gcc/testsuite/g++.dg/expr/discarded1a.C
>
> diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
> index c6b52f07050..4424670356c 100644
> --- a/gcc/cp/cvt.cc
> +++ b/gcc/cp/cvt.cc
> @@ -1250,9 +1250,10 @@ convert_to_void (tree expr, impl_conv_void implicit,
> tsubst_flags_t complain)
> case INDIRECT_REF:
> {
> tree type = TREE_TYPE (expr);
> - int is_reference = TYPE_REF_P (TREE_TYPE (TREE_OPERAND (expr, 0)));
Oops, this removal of is_reference should happen in the follow-up patch
instead, consider that fixed.
> int is_volatile = TYPE_VOLATILE (type);
> - int is_complete = COMPLETE_TYPE_P (complete_type (type));
> + if (is_volatile)
> + complete_type (type);
> + int is_complete = COMPLETE_TYPE_P (type);
>
> /* Can't load the value if we don't know the type. */
> if (is_volatile && !is_complete)
> @@ -1412,9 +1413,10 @@ convert_to_void (tree expr, impl_conv_void implicit,
> tsubst_flags_t complain)
> {
> /* External variables might be incomplete. */
> tree type = TREE_TYPE (expr);
> - int is_complete = COMPLETE_TYPE_P (complete_type (type));
>
> - if (TYPE_VOLATILE (type) && !is_complete && (complain & tf_warning))
> + if (TYPE_VOLATILE (type)
> + && !COMPLETE_TYPE_P (complete_type (type))
> + && (complain & tf_warning))
> switch (implicit)
> {
> case ICV_CAST:
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires36.C
> b/gcc/testsuite/g++.dg/cpp2a/concepts-requires36.C
> new file mode 100644
> index 00000000000..8d3a4fcd2aa
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires36.C
> @@ -0,0 +1,16 @@
> +// PR c++/111419
> +// { dg-do compile { target c++20 } }
> +
> +template<class F>
> +concept invocable = requires(F& f) { f(); };
> +
> +template<class F>
> +concept deref_invocable = requires(F& f) { *f(); };
> +
> +struct Incomplete;
> +
> +template<class T>
> +struct Holder { T t; };
> +
> +static_assert(invocable<Holder<Incomplete>& ()>);
> +static_assert(deref_invocable<Holder<Incomplete>* ()>);
> diff --git a/gcc/testsuite/g++.dg/expr/discarded1.C
> b/gcc/testsuite/g++.dg/expr/discarded1.C
> new file mode 100644
> index 00000000000..c0c22e9e95b
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/expr/discarded1.C
> @@ -0,0 +1,15 @@
> +// PR c++/111419
> +
> +struct Incomplete;
> +
> +template<class T> struct Holder { T t; }; // { dg-bogus "incomplete" }
> +
> +extern Holder<Incomplete> a;
> +extern Holder<Incomplete>& b;
> +extern Holder<Incomplete>* c;
> +
> +int main() {
> + a;
> + b;
> + *c;
> +}
> diff --git a/gcc/testsuite/g++.dg/expr/discarded1a.C
> b/gcc/testsuite/g++.dg/expr/discarded1a.C
> new file mode 100644
> index 00000000000..1c4dff4553e
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/expr/discarded1a.C
> @@ -0,0 +1,17 @@
> +// A version of discarded1.C using volatile types.
> +// PR c++/111419
> +
> +struct Incomplete;
> +
> +template<class T, int> struct Holder { T t; }; // { dg-error "incomplete" }
> +
> +extern volatile Holder<Incomplete, 0> a;
> +extern volatile Holder<Incomplete, 1>& b;
> +extern volatile Holder<Incomplete, 2>* c;
> +
> +int main() {
> + a; // { dg-message "required from here" }
> + b; // { dg-message "required from here" }
> + // { dg-warning "implicit dereference will not access object" "" { target
> *-*-* } .-1 }
> + *c; // { dg-message "required from here" }
> +}
> --
> 2.42.0.216.gbda494f404
>
>
