Revert "GCC ABI Compatibility: Preserve alignment of non-pod members in packed structs"

This reverts commit 2771233.

There are still some issues with this change to be worked out, so revert
this patch to avoid having to change ABIs from LLVM 13->14 and then again from
LLVM 14->15.  See discussion in https://reviews.llvm.org/D118511

Author: tstellar

clang/docs/ReleaseNotes.rst

@@ -338,12 +338,6 @@ ABI Changes in Clang
   is still in the process of being stabilized, so this type should not yet be
   used in interfaces that require ABI stability.
 
-- 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).
-  You can switch back to the old ABI behavior with the flag:
-  ``-fclang-abi-compat=13.0``.
-
 OpenMP Support in Clang
 -----------------------
 

clang/include/clang/Basic/LangOptions.h

@@ -181,10 +181,6 @@ class LangOptions : public LangOptionsBase {
     /// global-scope inline variables incorrectly.
     Ver12,
 
-    /// Attempt to be ABI-compatible with code generated by Clang 13.0.x.
-    /// This causes clang to not pack non-POD members of packed structs.
-    Ver13,
-
     /// Conform to the underlying platform's C and C++ ABIs as closely
     /// as we can.
     Latest

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -1887,12 +1887,7 @@ void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
   UnfilledBitsInLastUnit = 0;
   LastBitfieldStorageUnitSize = 0;
 
-  llvm::Triple Target = Context.getTargetInfo().getTriple();
-  bool FieldPacked = (Packed && (!FieldClass || FieldClass->isPOD() ||
-                                 Context.getLangOpts().getClangABICompat() <=
-                                     LangOptions::ClangABI::Ver13 ||
-                                 Target.isPS4() || Target.isOSDarwin())) ||
-                     D->hasAttr<PackedAttr>();
+  bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
 
   AlignRequirementKind AlignRequirement = AlignRequirementKind::None;
   CharUnits FieldSize;

clang/lib/Frontend/CompilerInvocation.cpp

@@ -3560,8 +3560,6 @@ void CompilerInvocation::GenerateLangArgs(const LangOptions &Opts,
     GenerateArg(Args, OPT_fclang_abi_compat_EQ, "11.0", SA);
   else if (Opts.getClangABICompat() == LangOptions::ClangABI::Ver12)
     GenerateArg(Args, OPT_fclang_abi_compat_EQ, "12.0", SA);
-  else if (Opts.getClangABICompat() == LangOptions::ClangABI::Ver13)
-    GenerateArg(Args, OPT_fclang_abi_compat_EQ, "13.0", SA);
 
   if (Opts.getSignReturnAddressScope() ==
       LangOptions::SignReturnAddressScopeKind::All)
@@ -4064,8 +4062,6 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
         Opts.setClangABICompat(LangOptions::ClangABI::Ver11);
       else if (Major <= 12)
         Opts.setClangABICompat(LangOptions::ClangABI::Ver12);
-      else if (Major <= 13)
-        Opts.setClangABICompat(LangOptions::ClangABI::Ver13);
     } else if (Ver != "latest") {
       Diags.Report(diag::err_drv_invalid_value)
           << A->getAsString(Args) << A->getValue();

clang/test/SemaCXX/class-layout.cpp

@@ -1,9 +1,6 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++98 -Wno-inaccessible-base
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base
-// RUN: %clang_cc1 -triple x86_64-apple-darwin    %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -DCLANG_ABI_COMPAT=13
-// RUN: %clang_cc1 -triple x86_64-scei-ps4        %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -DCLANG_ABI_COMPAT=6
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=6 -DCLANG_ABI_COMPAT=6
-// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -fclang-abi-compat=13 -DCLANG_ABI_COMPAT=13
 // expected-no-diagnostics
 
 #define SA(n, p) int a##n[(p) ? 1 : -1]
@@ -607,37 +604,3 @@ namespace PR37275 {
 #endif
 #pragma pack(pop)
 }
-
-namespace non_pod {
-struct t1 {
-protected:
-  int a;
-};
-// GCC prints warning: ignoring packed attribute because of unpacked non-POD field 't1 t2::v1'`
-struct t2 {
-  char c1;
-  short s1;
-  char c2;
-  t1 v1;
-} __attribute__((packed));
-#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 13
-_Static_assert(_Alignof(t1) == 4, "");
-_Static_assert(_Alignof(t2) == 1, "");
-#else
-_Static_assert(_Alignof(t1) == 4, "");
-_Static_assert(_Alignof(t2) == 4, "");
-#endif
-_Static_assert(sizeof(t2) == 8, ""); // it's still packing the rest of the struct
-} // namespace non_pod
-
-namespace non_pod_packed {
-struct t1 {
-protected:
-  int a;
-} __attribute__((packed));
-struct t2 {
-  t1 v1;
-} __attribute__((packed));
-_Static_assert(_Alignof(t1) == 1, "");
-_Static_assert(_Alignof(t2) == 1, "");
-} // namespace non_pod_packed