[PATCH] c++: "more constrained" vs staticness of memfn [PR103783]

[PATCH] c++: "more constrained" vs staticness of memfn [PR103783]

[Patrick Palka]

Here we're rejecting the calls to g1 and g2 as ambiguous even though one
overload is more constrained than the other (and otherwise equivalent),
because the implicit 'this' parameter of the non-static overload causes
cand_parms_match to think the function parameter lists aren't equivalent.

This patch fixes this by making cand_parms_match skip over 'this'
appropriately.  Note that this bug only occurs with non-template member
functions because for the template case more_specialized_fns seems to
already skips over 'this' appropriately.

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

	PR c++/103783

gcc/cp/ChangeLog:

	* call.c (cand_parms_match): Skip over 'this' when given one
	static and one non-static member function.  Declare static.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-memfun2.C: New test.
---
 gcc/cp/call.c                                 | 17 ++++++++++---
 gcc/testsuite/g++.dg/cpp2a/concepts-memfun2.C | 25 +++++++++++++++++++
 2 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-memfun2.C

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 7f7ee88deed..ed74b907828 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -11918,7 +11918,7 @@ joust_maybe_elide_copy (z_candidate *&cand)
 /* True if the defining declarations of the two candidates have equivalent
    parameters.  */
 
-bool
+static bool
 cand_parms_match (z_candidate *c1, z_candidate *c2)
 {
   tree fn1 = c1->fn;
@@ -11940,8 +11940,19 @@ cand_parms_match (z_candidate *c1, z_candidate *c2)
       fn1 = DECL_TEMPLATE_RESULT (t1);
       fn2 = DECL_TEMPLATE_RESULT (t2);
     }
-  return compparms (TYPE_ARG_TYPES (TREE_TYPE (fn1)),
-		    TYPE_ARG_TYPES (TREE_TYPE (fn2)));
+  tree parms1 = TYPE_ARG_TYPES (TREE_TYPE (fn1));
+  tree parms2 = TYPE_ARG_TYPES (TREE_TYPE (fn2));
+  if (DECL_FUNCTION_MEMBER_P (fn1)
+      && DECL_FUNCTION_MEMBER_P (fn2)
+      && (DECL_NONSTATIC_MEMBER_FUNCTION_P (fn1)
+	  != DECL_NONSTATIC_MEMBER_FUNCTION_P (fn2)))
+    {
+      /* Ignore 'this' when comparing the parameters of a static member
+	 function with those of a non-static one.  */
+      parms1 = skip_artificial_parms_for (fn1, parms1);
+      parms2 = skip_artificial_parms_for (fn2, parms2);
+    }
+  return compparms (parms1, parms2);
 }
 
 /* Compare two candidates for overloading as described in
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-memfun2.C b/gcc/testsuite/g++.dg/cpp2a/concepts-memfun2.C
new file mode 100644
index 00000000000..e3845e48387
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-memfun2.C
@@ -0,0 +1,25 @@
+// PR c++/103783
+// { dg-do compile { target c++20 } }
+
+template<bool B>
+struct A {
+  template<class...> void f1() = delete;
+  template<class...> static void f1() requires B;
+
+  template<class...> void f2() requires B;
+  template<class...> static void f2() = delete;
+
+  void g1() = delete;
+  static void g1() requires B;
+
+  void g2() requires B;
+  static void g2() = delete;
+};
+
+int main() {
+  A<true> a;
+  a.f1(); // OK
+  a.f2(); // OK
+  a.g1(); // OK, previously rejected as ambiguous
+  a.g2(); // OK, previously rejected as ambiguous
+}
-- 
2.34.1.428.gdcc0cd074f

Re: [PATCH] c++: "more constrained" vs staticness of memfn [PR103783]

[Jason Merrill]

On 1/4/22 13:01, Patrick Palka wrote:
> Here we're rejecting the calls to g1 and g2 as ambiguous even though one
> overload is more constrained than the other (and otherwise equivalent),
> because the implicit 'this' parameter of the non-static overload causes
> cand_parms_match to think the function parameter lists aren't equivalent.
> 
> This patch fixes this by making cand_parms_match skip over 'this'
> appropriately.  Note that this bug only occurs with non-template member
> functions because for the template case more_specialized_fns seems to
> already skips over 'this' appropriately.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk and perhaps 11?

OK for both.

> 	PR c++/103783
> 
> gcc/cp/ChangeLog:
> 
> 	* call.c (cand_parms_match): Skip over 'this' when given one
> 	static and one non-static member function.  Declare static.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/concepts-memfun2.C: New test.
> ---
>   gcc/cp/call.c                                 | 17 ++++++++++---
>   gcc/testsuite/g++.dg/cpp2a/concepts-memfun2.C | 25 +++++++++++++++++++
>   2 files changed, 39 insertions(+), 3 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-memfun2.C
> 
> diff --git a/gcc/cp/call.c b/gcc/cp/call.c
> index 7f7ee88deed..ed74b907828 100644
> --- a/gcc/cp/call.c
> +++ b/gcc/cp/call.c
> @@ -11918,7 +11918,7 @@ joust_maybe_elide_copy (z_candidate *&cand)
>   /* True if the defining declarations of the two candidates have equivalent
>      parameters.  */
>   
> -bool
> +static bool
>   cand_parms_match (z_candidate *c1, z_candidate *c2)
>   {
>     tree fn1 = c1->fn;
> @@ -11940,8 +11940,19 @@ cand_parms_match (z_candidate *c1, z_candidate *c2)
>         fn1 = DECL_TEMPLATE_RESULT (t1);
>         fn2 = DECL_TEMPLATE_RESULT (t2);
>       }
> -  return compparms (TYPE_ARG_TYPES (TREE_TYPE (fn1)),
> -		    TYPE_ARG_TYPES (TREE_TYPE (fn2)));
> +  tree parms1 = TYPE_ARG_TYPES (TREE_TYPE (fn1));
> +  tree parms2 = TYPE_ARG_TYPES (TREE_TYPE (fn2));
> +  if (DECL_FUNCTION_MEMBER_P (fn1)
> +      && DECL_FUNCTION_MEMBER_P (fn2)
> +      && (DECL_NONSTATIC_MEMBER_FUNCTION_P (fn1)
> +	  != DECL_NONSTATIC_MEMBER_FUNCTION_P (fn2)))
> +    {
> +      /* Ignore 'this' when comparing the parameters of a static member
> +	 function with those of a non-static one.  */
> +      parms1 = skip_artificial_parms_for (fn1, parms1);
> +      parms2 = skip_artificial_parms_for (fn2, parms2);
> +    }
> +  return compparms (parms1, parms2);
>   }
>   
>   /* Compare two candidates for overloading as described in
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-memfun2.C b/gcc/testsuite/g++.dg/cpp2a/concepts-memfun2.C
> new file mode 100644
> index 00000000000..e3845e48387
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-memfun2.C
> @@ -0,0 +1,25 @@
> +// PR c++/103783
> +// { dg-do compile { target c++20 } }
> +
> +template<bool B>
> +struct A {
> +  template<class...> void f1() = delete;
> +  template<class...> static void f1() requires B;
> +
> +  template<class...> void f2() requires B;
> +  template<class...> static void f2() = delete;
> +
> +  void g1() = delete;
> +  static void g1() requires B;
> +
> +  void g2() requires B;
> +  static void g2() = delete;
> +};
> +
> +int main() {
> +  A<true> a;
> +  a.f1(); // OK
> +  a.f2(); // OK
> +  a.g1(); // OK, previously rejected as ambiguous
> +  a.g2(); // OK, previously rejected as ambiguous
> +}