Re: [PATCH] c++: some missing-SFINAE fixes

[Jason Merrill <jason@redhat.com>]

On 9/13/22 09:46, Patrick Palka wrote:
> On Tue, 13 Sep 2022, Jason Merrill wrote:
> 
>> On 9/13/22 07:45, Patrick Palka wrote:
>>> It looks like we aren't respecting SFINAE for:
>>>
>>>     * an invalid/non-constant conditional explicit-specifier
>>>     * a non-constant conditional noexcept-specifier
>>>     * a non-constant argument to __integer_pack
>>>
>>> This patch fixes these issues in the usual way, by passing complain
>>> and propagating error_mark_node appropriately.
>>>
>>> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
>>> trunk?
>>>
>>> gcc/cp/ChangeLog:
>>>
>>> 	* decl.cc (build_explicit_specifier): Pass complain to
>>> 	cxx_constant_value.
>>> 	* except.cc (build_noexcept_spec): Likewise.
>>> 	* pt.cc (expand_integer_pack): Likewise.
>>> 	(tsubst_function_decl): Propagate error_mark_node returned
>>> 	from build_explicit_specifier.
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>> 	* g++.dg/cpp1z/noexcept-type26.C: New test.
>>> 	* g++.dg/cpp2a/explicit19.C: New test.
>>> 	* g++.dg/ext/integer-pack6.C: New test.
>>> ---
>>>    gcc/cp/decl.cc                               |  2 +-
>>>    gcc/cp/except.cc                             |  2 +-
>>>    gcc/cp/pt.cc                                 |  6 ++++--
>>>    gcc/testsuite/g++.dg/cpp1z/noexcept-type26.C | 12 ++++++++++++
>>>    gcc/testsuite/g++.dg/cpp2a/explicit19.C      | 12 ++++++++++++
>>>    gcc/testsuite/g++.dg/ext/integer-pack6.C     | 13 +++++++++++++
>>>    6 files changed, 43 insertions(+), 4 deletions(-)
>>>    create mode 100644 gcc/testsuite/g++.dg/cpp1z/noexcept-type26.C
>>>    create mode 100644 gcc/testsuite/g++.dg/cpp2a/explicit19.C
>>>    create mode 100644 gcc/testsuite/g++.dg/ext/integer-pack6.C
>>>
>>> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
>>> index 936f1cf0197..5404d7e084c 100644
>>> --- a/gcc/cp/decl.cc
>>> +++ b/gcc/cp/decl.cc
>>> @@ -18557,7 +18557,7 @@ build_explicit_specifier (tree expr, tsubst_flags_t
>>> complain)
>>>        expr = build_converted_constant_bool_expr (expr, complain);
>>>      expr = instantiate_non_dependent_expr (expr, complain);
>>> -  expr = cxx_constant_value (expr);
>>> +  expr = cxx_constant_value (expr, NULL_TREE, complain);
>>
>> The patch is OK, but perhaps we want another overload that omits the object
>> parameter?
> 
> Thanks -- sounds good, like the following incremental patch?

OK.

> -- >8 --
> 
> Subject: [PATCH] c++: two-parameter version of cxx_constant_value
> 
> Since some callers need the complain parameter but not the object
> parameter, let's introduce and use an overload of cxx_constant_value
> that omits the latter.
> 
> gcc/cp/ChangeLog:
> 
> 	* cp-tree.h (cxx_constant_value): Define two-parameter version
> 	that omits the object parameter.
> 	* decl.cc (build_explicit_specifier): Omit NULL_TREE object
> 	argument to cxx_constant_value.
> 	* except.cc (build_noexcept_spec): Likewise.
> 	* pt.cc (expand_integer_pack): Likewise.
> 	(fold_targs_r): Likewise.
> 	* semantics.cc (finish_if_stmt_cond): Likewise.
> ---
>   gcc/cp/cp-tree.h    | 2 ++
>   gcc/cp/decl.cc      | 2 +-
>   gcc/cp/except.cc    | 2 +-
>   gcc/cp/pt.cc        | 4 ++--
>   gcc/cp/semantics.cc | 2 +-
>   5 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
> index 2ba44e80e20..1eb176d4a50 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -8414,6 +8414,8 @@ extern bool require_rvalue_constant_expression (tree);
>   extern bool require_potential_rvalue_constant_expression (tree);
>   extern tree cxx_constant_value			(tree, tree = NULL_TREE,
>   						 tsubst_flags_t = tf_error);
> +inline tree cxx_constant_value (tree t, tsubst_flags_t complain)
> +{ return cxx_constant_value (t, NULL_TREE, complain); }
>   extern void cxx_constant_dtor			(tree, tree);
>   extern tree cxx_constant_init			(tree, tree = NULL_TREE);
>   extern tree maybe_constant_value		(tree, tree = NULL_TREE, bool = false);
> diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
> index 5404d7e084c..006e9affcba 100644
> --- a/gcc/cp/decl.cc
> +++ b/gcc/cp/decl.cc
> @@ -18557,7 +18557,7 @@ build_explicit_specifier (tree expr, tsubst_flags_t complain)
>   
>     expr = build_converted_constant_bool_expr (expr, complain);
>     expr = instantiate_non_dependent_expr (expr, complain);
> -  expr = cxx_constant_value (expr, NULL_TREE, complain);
> +  expr = cxx_constant_value (expr, complain);
>     return expr;
>   }
>   
> diff --git a/gcc/cp/except.cc b/gcc/cp/except.cc
> index 4d7f0ce102d..048612de400 100644
> --- a/gcc/cp/except.cc
> +++ b/gcc/cp/except.cc
> @@ -1257,7 +1257,7 @@ build_noexcept_spec (tree expr, tsubst_flags_t complain)
>       {
>         expr = build_converted_constant_bool_expr (expr, complain);
>         expr = instantiate_non_dependent_expr (expr, complain);
> -      expr = cxx_constant_value (expr, NULL_TREE, complain);
> +      expr = cxx_constant_value (expr, complain);
>       }
>     if (TREE_CODE (expr) == INTEGER_CST)
>       {
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 074179288b6..db4e808adec 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -3869,7 +3869,7 @@ expand_integer_pack (tree call, tree args, tsubst_flags_t complain,
>     else
>       {
>         hi = instantiate_non_dependent_expr (hi, complain);
> -      hi = cxx_constant_value (hi, NULL_TREE, complain);
> +      hi = cxx_constant_value (hi, complain);
>         int len = valid_constant_size_p (hi) ? tree_to_shwi (hi) : -1;
>   
>         /* Calculate the largest value of len that won't make the size of the vec
> @@ -20121,7 +20121,7 @@ fold_targs_r (tree targs, tsubst_flags_t complain)
>   	       && !glvalue_p (elt)
>   	       && !TREE_CONSTANT (elt))
>   	{
> -	  elt = cxx_constant_value (elt, NULL_TREE, complain);
> +	  elt = cxx_constant_value (elt, complain);
>   	  if (elt == error_mark_node)
>   	    return false;
>   	}
> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> index 3edefb2fca2..4f189978484 100644
> --- a/gcc/cp/semantics.cc
> +++ b/gcc/cp/semantics.cc
> @@ -1042,7 +1042,7 @@ finish_if_stmt_cond (tree orig_cond, tree if_stmt)
>       {
>         maybe_warn_for_constant_evaluated (cond, /*constexpr_if=*/true);
>         cond = instantiate_non_dependent_expr (cond);
> -      cond = cxx_constant_value (cond, NULL_TREE);
> +      cond = cxx_constant_value (cond);
>       }
>     else
>       {