[gcc r15-9664] c+: -Wabi false positive [PR120012]

[Jason Merrill via Gcc-cvs]

https://gcc.gnu.org/g:c9e3181516f1c0786f81b9c813581bf986a6300a

commit r15-9664-gc9e3181516f1c0786f81b9c813581bf986a6300a
Author: Jason Merrill <ja...@redhat.com>
Date:   Mon May 12 11:53:03 2025 -0400

    c+: -Wabi false positive [PR120012]
    
    The warning compares the position of a field depending on whether or not the
    previous base/field is considered a POD for layout, but failed to consider
    whether the previous base/field is empty; layout of an empty base doesn't
    consider PODness.
    
            PR c++/120012
    
    gcc/cp/ChangeLog:
    
            * class.cc (check_non_pod_aggregate): Check is_empty_class.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/abi/base-defaulted2.C: New test.
    
    (cherry picked from commit b4b4dfbd22e06877052bd4cc4b191d9d138155cf)

Diff:
---
 gcc/cp/class.cc                            |  6 ++++--
 gcc/testsuite/g++.dg/abi/base-defaulted2.C | 12 ++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/class.cc b/gcc/cp/class.cc
index 6767ac10358b..93ad9d6fd0b6 100644
--- a/gcc/cp/class.cc
+++ b/gcc/cp/class.cc
@@ -6835,8 +6835,10 @@ check_non_pod_aggregate (tree field)
   tree type = TREE_TYPE (field);
   if (TYPE_IDENTIFIER (type) == as_base_identifier)
     type = TYPE_CONTEXT (type);
-  if (!CLASS_TYPE_P (type) || (!CLASSTYPE_NON_POD_AGGREGATE (type)
-                              && !CLASSTYPE_NON_AGGREGATE_POD (type)))
+  if (!CLASS_TYPE_P (type)
+      || is_empty_class (type)
+      || (!CLASSTYPE_NON_POD_AGGREGATE (type)
+         && !CLASSTYPE_NON_AGGREGATE_POD (type)))
     return;
   tree size = end_of_class (type, (DECL_FIELD_IS_BASE (field)
                                   ? eoc_nvsize : eoc_nv_or_dsize));
diff --git a/gcc/testsuite/g++.dg/abi/base-defaulted2.C 
b/gcc/testsuite/g++.dg/abi/base-defaulted2.C
new file mode 100644
index 000000000000..9652ae60c037
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/base-defaulted2.C
@@ -0,0 +1,12 @@
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fabi-version=20 -Wabi" }
+
+struct Base {
+protected:
+  Base() = default;
+  ~Base() = default;
+};
+
+struct Derived : Base {
+  void* ptr;                   // { dg-bogus "offset" }
+};