Re: [PATCH] c++: Fix ICE with ill-formed array list-initialization [PR93712]

[Jason Merrill <jason@redhat.com>]

On 2/13/20 8:56 PM, Marek Polacek wrote:
> My P0388R4 patch changed build_array_conv to create an identity
> conversion at the start of the conversion chain.

Hmm, an identity conversion of {} suggests that it has a type, which it 
doesn't in the language.  I'm not strongly against it, but what was the 
reason for this change?

> That was a sound change but now we crash in convert_like_real
> 
>   7457     case ck_identity:
>   7458       if (BRACE_ENCLOSED_INITIALIZER_P (expr))
>   7459         {
>   7460           int nelts = CONSTRUCTOR_NELTS (expr);
>   7461           if (nelts == 0)
>   7462             expr = build_value_init (totype, complain);
>   7463           else if (nelts == 1)
>   7464             expr = CONSTRUCTOR_ELT (expr, 0)->value;
>   7465           else
>   7466             gcc_unreachable ();  // HERE
>   7467         }

Right, this is assuming that any other {} will either be ill-formed or 
handled by ck_aggr or ck_list.  How are we getting here without going 
through one of those?

> in a test like this
> 
>    int f (int const (&)[2])
>    {
>      return f({1, " "});
>    }
> 
> I considered fixing this when performing overload resolution (clang says
> "no matching function for call to 'f'"), but then it occured to me that
> we crash in different contexts too, so I'm just turning the assert into
> an early return.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> 2020-02-13  Marek Polacek  <polacek@redhat.com>
> 
> 	PR c++/93712 - ICE with ill-formed array list-initialization.
> 	* call.c (convert_like_real): Turn an assert into a return.
> 
> 	* g++.dg/cpp0x/initlist-array11.C: New test.
> ---
>   gcc/cp/call.c                                 |  2 +-
>   gcc/testsuite/g++.dg/cpp0x/initlist-array11.C | 10 ++++++++++
>   2 files changed, 11 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/initlist-array11.C
> 
> diff --git a/gcc/cp/call.c b/gcc/cp/call.c
> index 51621b7dd87..eba0ed8041d 100644
> --- a/gcc/cp/call.c
> +++ b/gcc/cp/call.c
> @@ -7463,7 +7463,7 @@ convert_like_real (conversion *convs, tree expr, tree fn, int argnum,
>   	  else if (nelts == 1)
>   	    expr = CONSTRUCTOR_ELT (expr, 0)->value;
>   	  else
> -	    gcc_unreachable ();
> +	    return error_mark_node;
>   	}
>         expr = mark_use (expr, /*rvalue_p=*/!convs->rvaluedness_matches_p,
>   		       /*read_p=*/true, UNKNOWN_LOCATION,
> diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist-array11.C b/gcc/testsuite/g++.dg/cpp0x/initlist-array11.C
> new file mode 100644
> index 00000000000..7e76b588471
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/initlist-array11.C
> @@ -0,0 +1,10 @@
> +// PR c++/93712 - ICE with ill-formed array list-initialization.
> +// { dg-do compile { target c++11 } }
> +
> +int f (const int (&)[2]);
> +
> +int g ()
> +{
> +  const int (&r)[2] = {1, "foo"}; // { dg-error "invalid conversion" }
> +  return f({1, "foo"}); // { dg-error "invalid conversion" }
> +}
> 
> base-commit: 1d69147af203d4dcd2270429f90c93f1a37ddfff
>