On Mon, 6 Mar 2023, Marek Polacek via Gcc-patches wrote:
> When processing a noexcept, constructors aren't elided: build_over_call
> has
> /* It's unsafe to elide the constructor when handling
> a noexcept-expression, it may evaluate to the wrong
> value (c++/53025). */
> && (force_elide || cp_noexcept_operand == 0))
> so the assert I added recently needs to be relaxed a little bit.
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
>
> PR c++/109030
>
> gcc/cp/ChangeLog:
>
> * constexpr.cc (cxx_eval_call_expression): Relax assert.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp0x/noexcept77.C: New test.
> ---
> gcc/cp/constexpr.cc | 6 +++++-
> gcc/testsuite/g++.dg/cpp0x/noexcept77.C | 9 +++++++++
> 2 files changed, 14 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/noexcept77.C
>
> diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> index 364695b762c..5384d0e8e46 100644
> --- a/gcc/cp/constexpr.cc
> +++ b/gcc/cp/constexpr.cc
> @@ -2869,7 +2869,11 @@ cxx_eval_call_expression (const constexpr_ctx *ctx,
> tree t,
>
> /* We used to shortcut trivial constructor/op= here, but nowadays
> we can only get a trivial function here with -fno-elide-constructors.
> */
> - gcc_checking_assert (!trivial_fn_p (fun) || !flag_elide_constructors);
> + gcc_checking_assert (!trivial_fn_p (fun)
> + || !flag_elide_constructors
> + /* We don't elide constructors when processing
> + a noexcept-expression. */
> + || cp_noexcept_operand);
It seems weird that we're performing constant evaluation within an
unevaluated operand. Would it make sense to also fix this a second way
by avoiding constant evaluation from maybe_constant_init when
cp_unevaluated_operand && !manifestly_const_eval, like in maybe_constant_value?
IIUC since we could still have an evaluated subexpression withis
noexcept, the two fixes would be complementary.
>
> bool non_constant_args = false;
> new_call.bindings
> diff --git a/gcc/testsuite/g++.dg/cpp0x/noexcept77.C
> b/gcc/testsuite/g++.dg/cpp0x/noexcept77.C
> new file mode 100644
> index 00000000000..16db8eb79ee
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/noexcept77.C
> @@ -0,0 +1,9 @@
> +// PR c++/109030
> +// { dg-do compile { target c++11 } }
> +
> +struct foo { };
> +
> +struct __as_receiver {
> + foo empty_env;
> +};
> +void sched(foo __fun) noexcept(noexcept(__as_receiver{__fun})) { }
>
> base-commit: dfb14cdd796ad9df6b5f2def047ef36b29385902
> --
> 2.39.2
>
>
