[PATCH] c++: decltype of non-dependent call of class type [PR105386]

[PATCH] c++: decltype of non-dependent call of class type [PR105386]

[Patrick Palka]

We need to pass tf_decltype when instantiating a non-dependent decltype
operand, like tsubst does in the dependent case, so that we avoid
materializing a temporary for a prvalue operand.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk/11?

	PR c++/105386

gcc/cp/ChangeLog:

	* semantics.cc (finish_decltype_type): Pass tf_decltype to
	instantiate_non_dependent_expr_sfinae.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/decltype81.C: New test.
---
 gcc/cp/semantics.cc                     |  2 +-
 gcc/testsuite/g++.dg/cpp0x/decltype81.C | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/decltype81.C

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index f08c0b6281f..ab48f11c9be 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -11252,7 +11252,7 @@ finish_decltype_type (tree expr, bool id_expression_or_member_access_p,
     }
   else if (processing_template_decl)
     {
-      expr = instantiate_non_dependent_expr_sfinae (expr, complain);
+      expr = instantiate_non_dependent_expr_sfinae (expr, complain|tf_decltype);
       if (expr == error_mark_node)
 	return error_mark_node;
       /* Keep processing_template_decl cleared for the rest of the function
diff --git a/gcc/testsuite/g++.dg/cpp0x/decltype81.C b/gcc/testsuite/g++.dg/cpp0x/decltype81.C
new file mode 100644
index 00000000000..7d25db39d9c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/decltype81.C
@@ -0,0 +1,15 @@
+// PR c++/105386
+// { dg-do compile { target c++11 } }
+
+template<class T> struct NoInst {
+  static_assert(sizeof(T) == 9999, "NoInst instantiated");
+};
+
+template<class T> NoInst<T> f(T);
+
+template<class>
+struct A {
+  using type = decltype(f(0));
+};
+
+A<int> a;
-- 
2.36.0.rc2.10.g1ac7422e39

Re: [PATCH] c++: decltype of non-dependent call of class type [PR105386]

[Jason Merrill]

On 4/26/22 09:45, Patrick Palka wrote:
> We need to pass tf_decltype when instantiating a non-dependent decltype
> operand, like tsubst does in the dependent case, so that we avoid
> materializing a temporary for a prvalue operand.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk/11?

OK.

> 	PR c++/105386
> 
> gcc/cp/ChangeLog:
> 
> 	* semantics.cc (finish_decltype_type): Pass tf_decltype to
> 	instantiate_non_dependent_expr_sfinae.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/decltype81.C: New test.
> ---
>   gcc/cp/semantics.cc                     |  2 +-
>   gcc/testsuite/g++.dg/cpp0x/decltype81.C | 15 +++++++++++++++
>   2 files changed, 16 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/decltype81.C
> 
> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> index f08c0b6281f..ab48f11c9be 100644
> --- a/gcc/cp/semantics.cc
> +++ b/gcc/cp/semantics.cc
> @@ -11252,7 +11252,7 @@ finish_decltype_type (tree expr, bool id_expression_or_member_access_p,
>       }
>     else if (processing_template_decl)
>       {
> -      expr = instantiate_non_dependent_expr_sfinae (expr, complain);
> +      expr = instantiate_non_dependent_expr_sfinae (expr, complain|tf_decltype);
>         if (expr == error_mark_node)
>   	return error_mark_node;
>         /* Keep processing_template_decl cleared for the rest of the function
> diff --git a/gcc/testsuite/g++.dg/cpp0x/decltype81.C b/gcc/testsuite/g++.dg/cpp0x/decltype81.C
> new file mode 100644
> index 00000000000..7d25db39d9c
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/decltype81.C
> @@ -0,0 +1,15 @@
> +// PR c++/105386
> +// { dg-do compile { target c++11 } }
> +
> +template<class T> struct NoInst {
> +  static_assert(sizeof(T) == 9999, "NoInst instantiated");
> +};
> +
> +template<class T> NoInst<T> f(T);
> +
> +template<class>
> +struct A {
> +  using type = decltype(f(0));
> +};
> +
> +A<int> a;