c++: alias template with dependent attributes [PR115897]
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Commit Message
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/14?
-- >8 --
Here we're prematurely stripping the dependent alias template-id A<T> to
its defining-type-id T when used as a template argument, which in turn
causes us to essentially ignore A's vector_size attribute. It seems this
has always been an issue for class template-ids, but after r14-2170
variable template-ids are affected as well.
To fix this, it seems natural to mark alias templates that have a
dependent attribute as complex, alongside e.g. constrained alias
templates, which prevents us from looking through them prematurely.
PR c++/115897
gcc/cp/ChangeLog:
* pt.cc (complex_alias_template_p): Return true for an alias
template with attributes.
(get_underlying_template): Don't look through an alias template
with attributes.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/alias-decl-77.C: New test.
---
gcc/cp/pt.cc | 10 +++++++
gcc/testsuite/g++.dg/cpp0x/alias-decl-77.C | 32 ++++++++++++++++++++++
2 files changed, 42 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-77.C
Comments
On 7/12/24 2:53 PM, Patrick Palka wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk/14?
>
> -- >8 --
>
> Here we're prematurely stripping the dependent alias template-id A<T> to
> its defining-type-id T when used as a template argument, which in turn
> causes us to essentially ignore A's vector_size attribute. It seems this
> has always been an issue for class template-ids, but after r14-2170
> variable template-ids are affected as well.
>
> To fix this, it seems natural to mark alias templates that have a
> dependent attribute as complex, alongside e.g. constrained alias
> templates, which prevents us from looking through them prematurely.
>
> PR c++/115897
>
> gcc/cp/ChangeLog:
>
> * pt.cc (complex_alias_template_p): Return true for an alias
> template with attributes.
> (get_underlying_template): Don't look through an alias template
> with attributes.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp0x/alias-decl-77.C: New test.
> ---
> gcc/cp/pt.cc | 10 +++++++
> gcc/testsuite/g++.dg/cpp0x/alias-decl-77.C | 32 ++++++++++++++++++++++
> 2 files changed, 42 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/cpp0x/alias-decl-77.C
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index e38e02488be..8239392923f 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -6628,6 +6628,11 @@ complex_alias_template_p (const_tree tmpl, tree *seen_out)
> if (get_constraints (tmpl))
> return true;
>
> + /* An alias with dependent type attributes is complex. */
> + if (any_dependent_type_attributes_p (DECL_ATTRIBUTES
> + (DECL_TEMPLATE_RESULT (tmpl))))
> + return true;
> +
> if (!complex_alias_tmpl_info)
> complex_alias_tmpl_info = hash_map<const_tree, tree>::create_ggc (13);
>
> @@ -6780,6 +6785,11 @@ get_underlying_template (tree tmpl)
> if (!at_least_as_constrained (underlying, tmpl))
> break;
>
> + /* If TMPL adds dependent attributes, it isn't equivalent. */
> + if (any_dependent_type_attributes_p (DECL_ATTRIBUTES
> + (DECL_TEMPLATE_RESULT (tmpl))))
> + break;
> +
> /* Alias is equivalent. Strip it and repeat. */
> tmpl = underlying;
> }
> diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-77.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-77.C
> new file mode 100644
> index 00000000000..d518c040a92
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-77.C
> @@ -0,0 +1,32 @@
> +// PR c++/115897
> +// { dg-do compile { target c++11 } }
> +
> +template<class T, class U>
> +struct is_same { static constexpr bool value = __is_same(T, U); };
> +
> +#if __cpp_variable_templates
> +template<class T, class U>
> +constexpr bool is_same_v = __is_same(T, U);
> +#endif
> +
> +template<class T>
> +using A [[gnu::vector_size(16)]] = T;
> +
> +template<class T>
> +using B = T;
> +
> +template<class T>
> +using C [[gnu::vector_size(16)]] = B<T>;
> +
> +template<class T>
> +void f() {
> + static_assert(!is_same<T, A<T>>::value, "");
> + static_assert(!is_same<T, C<T>>::value, "");
How about a positive test that A<T> and C<T> are the same? OK with that
change.
> +#if __cpp_variable_templates
> + static_assert(!is_same_v<T, A<T>>, "");
> + static_assert(!is_same_v<T, C<T>>, "");
> +#endif
> +};
> +
> +template void f<float>();
@@ -6628,6 +6628,11 @@ complex_alias_template_p (const_tree tmpl, tree *seen_out)
if (get_constraints (tmpl))
return true;
+ /* An alias with dependent type attributes is complex. */
+ if (any_dependent_type_attributes_p (DECL_ATTRIBUTES
+ (DECL_TEMPLATE_RESULT (tmpl))))
+ return true;
+
if (!complex_alias_tmpl_info)
complex_alias_tmpl_info = hash_map<const_tree, tree>::create_ggc (13);
@@ -6780,6 +6785,11 @@ get_underlying_template (tree tmpl)
if (!at_least_as_constrained (underlying, tmpl))
break;
+ /* If TMPL adds dependent attributes, it isn't equivalent. */
+ if (any_dependent_type_attributes_p (DECL_ATTRIBUTES
+ (DECL_TEMPLATE_RESULT (tmpl))))
+ break;
+
/* Alias is equivalent. Strip it and repeat. */
tmpl = underlying;
}
new file mode 100644
@@ -0,0 +1,32 @@
+// PR c++/115897
+// { dg-do compile { target c++11 } }
+
+template<class T, class U>
+struct is_same { static constexpr bool value = __is_same(T, U); };
+
+#if __cpp_variable_templates
+template<class T, class U>
+constexpr bool is_same_v = __is_same(T, U);
+#endif
+
+template<class T>
+using A [[gnu::vector_size(16)]] = T;
+
+template<class T>
+using B = T;
+
+template<class T>
+using C [[gnu::vector_size(16)]] = B<T>;
+
+template<class T>
+void f() {
+ static_assert(!is_same<T, A<T>>::value, "");
+ static_assert(!is_same<T, C<T>>::value, "");
+
+#if __cpp_variable_templates
+ static_assert(!is_same_v<T, A<T>>, "");
+ static_assert(!is_same_v<T, C<T>>, "");
+#endif
+};
+
+template void f<float>();