c++: unifying FUNCTION_DECLs [PR93740]
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Commit Message
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look
OK for trunk? I considered removing the is_overloaded_fn test now as
well, but it could in theory be hit (and not subsumed by the
type_unknown_p test) for e.g. OVERLOAD of a single FUNCTION_DECL. I
wonder if that's something we'd see here? If not, I can remove the
test. It seems safe to remove as far as the testsuite is concerned.
-- >8 --
unify currently always returns success when unifying two FUNCTION_DECLs
(due to the is_overloaded_fn deferment within the default case), which
means for the below testcase unify incorrectly matches &A::foo with
&A::bar, which leads to deduction failure for the index_of calls due to
a bogus base class ambiguity.
This patch makes us instead handle unification of FUNCTION_DECL like
other decls, i.e. according to their identity.
PR c++/93740
gcc/cp/ChangeLog:
* pt.cc (unify) <case FUNCTION_DECL>: Handle it like FIELD_DECL
and TEMPLATE_DECL.
gcc/testsuite/ChangeLog:
* g++.dg/template/ptrmem34.C: New test.
---
gcc/cp/pt.cc | 1 +
gcc/testsuite/g++.dg/template/ptrmem34.C | 27 ++++++++++++++++++++++++
2 files changed, 28 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/template/ptrmem34.C
Comments
On 12/12/23 13:40, Patrick Palka wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look
> OK for trunk?
OK.
> I considered removing the is_overloaded_fn test now as
> well, but it could in theory be hit (and not subsumed by the
> type_unknown_p test) for e.g. OVERLOAD of a single FUNCTION_DECL. I
> wonder if that's something we'd see here? If not, I can remove the
> test. It seems safe to remove as far as the testsuite is concerned.
Next stage 1, sure.
> -- >8 --
>
> unify currently always returns success when unifying two FUNCTION_DECLs
> (due to the is_overloaded_fn deferment within the default case), which
> means for the below testcase unify incorrectly matches &A::foo with
> &A::bar, which leads to deduction failure for the index_of calls due to
> a bogus base class ambiguity.
>
> This patch makes us instead handle unification of FUNCTION_DECL like
> other decls, i.e. according to their identity.
>
> PR c++/93740
>
> gcc/cp/ChangeLog:
>
> * pt.cc (unify) <case FUNCTION_DECL>: Handle it like FIELD_DECL
> and TEMPLATE_DECL.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/template/ptrmem34.C: New test.
> ---
> gcc/cp/pt.cc | 1 +
> gcc/testsuite/g++.dg/template/ptrmem34.C | 27 ++++++++++++++++++++++++
> 2 files changed, 28 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/template/ptrmem34.C
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index c2ddbff405b..a8966e223f1 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -24967,6 +24967,7 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
> gcc_unreachable ();
>
> case FIELD_DECL:
> + case FUNCTION_DECL:
> case TEMPLATE_DECL:
> /* Matched cases are handled by the ARG == PARM test above. */
> return unify_template_argument_mismatch (explain_p, parm, arg);
> diff --git a/gcc/testsuite/g++.dg/template/ptrmem34.C b/gcc/testsuite/g++.dg/template/ptrmem34.C
> new file mode 100644
> index 00000000000..c349ca55639
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/template/ptrmem34.C
> @@ -0,0 +1,27 @@
> +// PR c++/93740
> +// { dg-do compile { target c++11 } }
> +
> +struct A {
> + void foo();
> + void bar();
> +};
> +
> +template <typename T, T val>
> +struct const_val{};
> +
> +template <int N, typename T>
> +struct indexed_elem{};
> +
> +using mem_fun_A_foo = const_val<decltype(&A::foo), &A::foo>;
> +using mem_fun_A_bar = const_val<decltype(&A::bar), &A::bar>;
> +
> +struct A_indexed_member_funcs
> + : indexed_elem<0, mem_fun_A_foo>,
> + indexed_elem<1, mem_fun_A_bar>
> +{};
> +
> +template <typename T, int N>
> +constexpr int index_of(indexed_elem<N, T>) { return N; }
> +
> +static_assert(index_of<mem_fun_A_foo>(A_indexed_member_funcs{}) == 0, "");
> +static_assert(index_of<mem_fun_A_bar>(A_indexed_member_funcs{}) == 1, "");
@@ -24967,6 +24967,7 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
gcc_unreachable ();
case FIELD_DECL:
+ case FUNCTION_DECL:
case TEMPLATE_DECL:
/* Matched cases are handled by the ARG == PARM test above. */
return unify_template_argument_mismatch (explain_p, parm, arg);
new file mode 100644
@@ -0,0 +1,27 @@
+// PR c++/93740
+// { dg-do compile { target c++11 } }
+
+struct A {
+ void foo();
+ void bar();
+};
+
+template <typename T, T val>
+struct const_val{};
+
+template <int N, typename T>
+struct indexed_elem{};
+
+using mem_fun_A_foo = const_val<decltype(&A::foo), &A::foo>;
+using mem_fun_A_bar = const_val<decltype(&A::bar), &A::bar>;
+
+struct A_indexed_member_funcs
+ : indexed_elem<0, mem_fun_A_foo>,
+ indexed_elem<1, mem_fun_A_bar>
+{};
+
+template <typename T, int N>
+constexpr int index_of(indexed_elem<N, T>) { return N; }
+
+static_assert(index_of<mem_fun_A_foo>(A_indexed_member_funcs{}) == 0, "");
+static_assert(index_of<mem_fun_A_bar>(A_indexed_member_funcs{}) == 1, "");