Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -814,13 +814,14 @@
 
 - GCC doesn't pack non-POD members in packed structs unless the packed
   attribute is also specified on the member. Clang historically did perform
-  such packing. Clang now matches the gcc behavior (except on Darwin and PS4).
+  such packing. Clang now matches the gcc behavior
+  (except on Darwin, PS4 and AIX).
   You can switch back to the old ABI behavior with the flag:
   ``-fclang-abi-compat=15.0``.
 - GCC allows POD types to have defaulted special members. Clang historically
   classified such types as non-POD (for the purposes of Itanium ABI). Clang now
-  matches the gcc behavior (except on Darwin and PS4). You can switch back to
-  the old ABI behavior with the flag: ``-fclang-abi-compat=15.0``.
+  matches the gcc behavior (except on Darwin, PS4, AIX and z/OS). You can switch
+  back to the old ABI behavior with the flag: ``-fclang-abi-compat=15.0``.
 
 OpenMP Support in Clang
 -----------------------
Index: clang/lib/AST/RecordLayoutBuilder.cpp
===================================================================
--- clang/lib/AST/RecordLayoutBuilder.cpp
+++ clang/lib/AST/RecordLayoutBuilder.cpp
@@ -1968,7 +1968,8 @@
                                  FieldClass->hasAttr<PackedAttr>() ||
                                  Context.getLangOpts().getClangABICompat() <=
                                      LangOptions::ClangABI::Ver15 ||
-                                 Target.isPS() || Target.isOSDarwin())) ||
+                                 Target.isPS() || Target.isOSDarwin() ||
+                                 Target.isOSAIX())) ||
                      D->hasAttr<PackedAttr>();
 
   // When used as part of a typedef, or together with a 'packed' attribute, the
Index: clang/lib/Basic/Targets/OSTargets.h
===================================================================
--- clang/lib/Basic/Targets/OSTargets.h
+++ clang/lib/Basic/Targets/OSTargets.h
@@ -773,6 +773,10 @@
   }
 
   bool defaultsToAIXPowerAlignment() const override { return true; }
+
+  bool areDefaultedSMFStillPOD(const LangOptions &) const override {
+    return false;
+  }
 };
 
 // z/OS target
@@ -831,6 +835,10 @@
     this->UseLeadingZeroLengthBitfield = false;
     this->ZeroLengthBitfieldBoundary = 32;
   }
+
+  bool areDefaultedSMFStillPOD(const LangOptions &) const override {
+    return false;
+  }
 };
 
 void addWindowsDefines(const llvm::Triple &Triple, const LangOptions &Opts,
Index: clang/test/SemaCXX/class-layout.cpp
===================================================================
--- clang/test/SemaCXX/class-layout.cpp
+++ clang/test/SemaCXX/class-layout.cpp
@@ -7,8 +7,17 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=14 -DCLANG_ABI_COMPAT=14
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=15 -DCLANG_ABI_COMPAT=15
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=16 -DCLANG_ABI_COMPAT=16
+// RUN: %clang_cc1 -triple powerpc-ibm-aix7.3.0.0 %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -DCLANG_ABI_COMPAT=15
+// RUN: %clang_cc1 -triple powerpc-ibm-aix7.3.0.0 %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=15 -DCLANG_ABI_COMPAT=15
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix7.3.0.0 %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -DCLANG_ABI_COMPAT=15
+// RUN: %clang_cc1 -triple powerpc64-ibm-aix7.3.0.0 %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=15 -DCLANG_ABI_COMPAT=15
+// RUN: %clang_cc1 -triple s390x-none-zos %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base
+// RUN: %clang_cc1 -triple s390x-none-zos %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=15 -DCLANG_ABI_COMPAT=15
+
 // expected-no-diagnostics
 
+#if !defined(__MVS__) && !defined(_AIX)
+
 #define SA(n, p) int a##n[(p) ? 1 : -1]
 
 struct A {
@@ -611,6 +620,8 @@
 #pragma pack(pop)
 }
 
+#endif // !defined(__MVS__) && !defined(__AIX__)
+
 namespace non_pod {
 struct t1 {
 protected:
@@ -670,11 +681,15 @@
 struct t2 {
   t1 v1;
 } __attribute__((packed));
+#if (defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 15) || !defined(__MVS__)
 _Static_assert(_Alignof(t2) == 1, "");
+#else
+_Static_assert(_Alignof(t2) == 4, "");
+#endif
 struct t3 : t1 {
   char c;
 };
-#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 15
+#if (defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 15) || defined(__MVS__)
 _Static_assert(sizeof(t3) == 8, "");
 #else
 _Static_assert(sizeof(t3) == 12, "");