[gcc r16-9732] c++: ICE with -Wsubobject-linkage and function type [PR127672]

[Marek Polacek via Gcc-cvs]

https://gcc.gnu.org/g:cb095f94da491f4d5e4df92abbc5d55792849e7d

commit r16-9732-gcb095f94da491f4d5e4df92abbc5d55792849e7d
Author: Marek Polacek <pola...@redhat.com>
Date:   Wed Sep 30 14:02:21 2026 -0400

    c++: ICE with -Wsubobject-linkage and function type [PR127672]
    
    Here we crash in decl_namespace_context because function types
    (or pointer-to-data-member types) like void() have no TYPE_MAIN_DECL:
    
             decl = CP_DECL_CONTEXT (TYPE_MAIN_DECL (decl));
    
    We got there from the constrain_class_visibility TYPE_FIELDS walk
    which emits the -Wsubobject-linkage warning.  And this test has:
    
      namespace { struct P { }; }
      struct S { void (*f) (P *); };
    
    I'm using OVERLOAD_TYPE_P, inspired by min_vis_r.
    
            PR c++/127672
    
    gcc/cp/ChangeLog:
    
            * decl2.cc (constrain_class_visibility): Check OVERLOAD_TYPE_P
            before calling decl_anon_ns_mem_p.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/warn/Wsubobject-linkage-6.C: New test.
    
    Reviewed-by: Jason Merrill <ja...@redhat.com>
    (cherry picked from commit 5f9f8711bf791130fd30bc1f04b2097f3ef25f0b)

Diff:
---
 gcc/cp/decl2.cc                                  |  1 +
 gcc/testsuite/g++.dg/warn/Wsubobject-linkage-6.C | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index 8bd893db7753..9e53a14267c9 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -3601,6 +3601,7 @@ constrain_class_visibility (tree type)
                               type, t, nlt);
                  }
                else if (cxx_dialect > cxx98
+                        && OVERLOAD_TYPE_P (ftype)
                         && !decl_anon_ns_mem_p (ftype))
                  warning (OPT_Wsubobject_linkage, "\
 %qT has a field %q#D whose type has internal linkage",
diff --git a/gcc/testsuite/g++.dg/warn/Wsubobject-linkage-6.C 
b/gcc/testsuite/g++.dg/warn/Wsubobject-linkage-6.C
new file mode 100644
index 000000000000..ea77f14386fe
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wsubobject-linkage-6.C
@@ -0,0 +1,10 @@
+// PR c++/127672
+// { dg-do compile { target c++11 } }
+
+namespace { struct P { }; }
+
+#line 7 "foo.C"
+struct S { void (*f) (P *); };   // { dg-warning "uses the anonymous 
namespace" }
+struct S2 { void (P::*m) (); };          // { dg-warning "uses the anonymous 
namespace" }
+struct S3 { P (*g) (); };        // { dg-warning "uses the anonymous 
namespace" }
+struct S4 { int P::*d; };        // { dg-warning "uses the anonymous 
namespace" }