[PATCH] c++: bogus warning with value init of const pmf [PR92752]

[PATCH] c++: bogus warning with value init of const pmf [PR92752]

[Patrick Palka]

Here we're emitting a -Wignored-qualifiers warning for an
intermediate compiler-generated cast of 0 to 'method-type* const'
as part of value initialization of a const pmf.  This patch
suppresses the warning by stripping cv-quals from this pointer
type before performing the cast.

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

	PR c++/92752

gcc/cp/ChangeLog:

	* typeck.cc (build_ptrmemfunc): Strip cv-quals from the pointer
	type after building the pmf type.

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wignored-qualifiers2.C: New test.
---
 gcc/cp/typeck.cc                                |  1 +
 .../g++.dg/warn/Wignored-qualifiers2.C          | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/warn/Wignored-qualifiers2.C

diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 11c9d8aff3e..0ce1cd3b6c8 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -9593,6 +9593,7 @@ build_ptrmemfunc (tree type, tree pfn, int force, bool c_cast_p,
   /* Handle null pointer to member function conversions.  */
   if (null_ptr_cst_p (pfn))
     {
+      type = cv_unqualified (type);
       pfn = cp_build_c_cast (input_location, type, pfn, complain);
       return build_ptrmemfunc1 (to_type,
 				integer_zero_node,
diff --git a/gcc/testsuite/g++.dg/warn/Wignored-qualifiers2.C b/gcc/testsuite/g++.dg/warn/Wignored-qualifiers2.C
new file mode 100644
index 00000000000..c4c37545c02
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wignored-qualifiers2.C
@@ -0,0 +1,17 @@
+// PR c++/92752
+// { dg-do compile }
+// { dg-additional-options "-Wignored-qualifiers" }
+
+struct X;
+
+template<class T>
+struct Wrap {
+  T data;
+  Wrap() : data() {}
+};
+
+typedef int (X::*type)();
+Wrap<const type> x;
+#if __cpp_initializer_lists
+const type t{};
+#endif
-- 
2.35.0

Re: [PATCH] c++: bogus warning with value init of const pmf [PR92752]

[Jason Merrill]

On 1/28/22 12:54, Patrick Palka wrote:
> Here we're emitting a -Wignored-qualifiers warning for an
> intermediate compiler-generated cast of 0 to 'method-type* const'
> as part of value initialization of a const pmf.  This patch
> suppresses the warning by stripping cv-quals from this pointer
> type before performing the cast.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk?
> 
> 	PR c++/92752
> 
> gcc/cp/ChangeLog:
> 
> 	* typeck.cc (build_ptrmemfunc): Strip cv-quals from the pointer
> 	type after building the pmf type.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/warn/Wignored-qualifiers2.C: New test.
> ---
>   gcc/cp/typeck.cc                                |  1 +
>   .../g++.dg/warn/Wignored-qualifiers2.C          | 17 +++++++++++++++++
>   2 files changed, 18 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wignored-qualifiers2.C
> 
> diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
> index 11c9d8aff3e..0ce1cd3b6c8 100644
> --- a/gcc/cp/typeck.cc
> +++ b/gcc/cp/typeck.cc
> @@ -9593,6 +9593,7 @@ build_ptrmemfunc (tree type, tree pfn, int force, bool c_cast_p,
>     /* Handle null pointer to member function conversions.  */
>     if (null_ptr_cst_p (pfn))
>       {
> +      type = cv_unqualified (type);
>         pfn = cp_build_c_cast (input_location, type, pfn, complain);

Maybe we want to cast to TYPE_PTRMEMFUNC_FN_TYPE_RAW (to_type) instead 
of "type" here?  OK with that change.

>         return build_ptrmemfunc1 (to_type,
>   				integer_zero_node,
> diff --git a/gcc/testsuite/g++.dg/warn/Wignored-qualifiers2.C b/gcc/testsuite/g++.dg/warn/Wignored-qualifiers2.C
> new file mode 100644
> index 00000000000..c4c37545c02
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wignored-qualifiers2.C
> @@ -0,0 +1,17 @@
> +// PR c++/92752
> +// { dg-do compile }
> +// { dg-additional-options "-Wignored-qualifiers" }
> +
> +struct X;
> +
> +template<class T>
> +struct Wrap {
> +  T data;
> +  Wrap() : data() {}
> +};
> +
> +typedef int (X::*type)();
> +Wrap<const type> x;
> +#if __cpp_initializer_lists
> +const type t{};
> +#endif