Re: [PATCH] c++: partially inst requires-expr in noexcept-spec [PR101043]

[Jason Merrill <jason@redhat.com>]

On 11/14/23 16:04, Patrick Palka wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?

OK.

> -- >8 --
> 
> Here we're ICEing from strip_typedefs for the partially instantiated
> requires-expression when walking its REQUIRES_EXPR_EXTRA_ARGS since it's
> a TREE_LIST with non-empty TREE_PURPOSE (to hold the captured local
> specialization 't' as per build_extra_args) which strip_typedefs doesn't
> expect.
> 
> We can probably skip walking REQUIRES_EXPR_EXTRA_ARGS at all since it
> shouldn't contain any typedefs in the first place, but it seems safer
> and more generally useful to just teach strip_typedefs to handle non-empty
> TREE_PURPOSE the obvious way.  (The handling asserted TREE_PURPOSE was
> empty ever since inception i.e. r189298.)
> 
> 	PR c++/101043
> 
> gcc/cp/ChangeLog:
> 
> 	* tree.cc (strip_typedefs_expr) <case TREE_LIST>: Handle
> 	non-empty TREE_PURPOSE.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/concepts-requires37.C: New test.
> ---
>   gcc/cp/tree.cc                                | 19 ++++++++++++-------
>   .../g++.dg/cpp2a/concepts-requires37.C        | 11 +++++++++++
>   2 files changed, 23 insertions(+), 7 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C
> 
> diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
> index dc4126f935c..0736e8d8f48 100644
> --- a/gcc/cp/tree.cc
> +++ b/gcc/cp/tree.cc
> @@ -1911,19 +1911,24 @@ strip_typedefs_expr (tree t, bool *remove_attributes, unsigned int flags)
>       case TREE_LIST:
>         {
>   	bool changed = false;
> -	releasing_vec vec;
> +	auto_vec<tree_pair, 4> vec;
>   	r = t;
>   	for (; t; t = TREE_CHAIN (t))
>   	  {
> -	    gcc_assert (!TREE_PURPOSE (t));
> -	    tree elt = strip_typedefs (TREE_VALUE (t),
> -				       remove_attributes, flags);
> -	    if (elt != TREE_VALUE (t))
> +	    tree purpose = strip_typedefs (TREE_PURPOSE (t),
> +					   remove_attributes, flags);
> +	    tree value = strip_typedefs (TREE_VALUE (t),
> +					 remove_attributes, flags);
> +	    if (purpose != TREE_PURPOSE (t) || value != TREE_VALUE (t))
>   	      changed = true;
> -	    vec_safe_push (vec, elt);
> +	    vec.safe_push ({purpose, value});
>   	  }
>   	if (changed)
> -	  r = build_tree_list_vec (vec);
> +	  {
> +	    r = NULL_TREE;
> +	    for (int i = vec.length () - 1; i >= 0; i--)
> +	      r = tree_cons (vec[i].first, vec[i].second, r);
> +	  }
>   	return r;
>         }
>   
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C
> new file mode 100644
> index 00000000000..72dad77fea1
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires37.C
> @@ -0,0 +1,11 @@
> +// PR c++/101043
> +// { dg-do compile { target c++20 } }
> +
> +template<class T>
> +void f(T t) {
> +  [&](auto) noexcept(requires { { t.g() }; }) { }(0);
> +}
> +
> +int main() {
> +  f(0);
> +}