Re: [PATCH] c++: noexcept and copy elision [PR109030]

[Jason Merrill <jason@redhat.com>]

On 3/6/23 18:59, Marek Polacek 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?

OK.

> 	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);
>   
>     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