Move GCC-compatible pod-packing change to v15/old behavior available at v14 and below

[dblaikie]

Summary

Since this didn't make it into the v14 release - anyone requesting the
v14 ABI shouldn't get this GCC-compatible change that isn't backwards
compatible with v14 Clang.

[MatzeB]

LGTM, thanks!

clang/docs/ReleaseNotes.rst

 
 ABI Changes in Clang
 --------------------
 
 - 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``.
+  ``-fclang-abi-compat=14.0``.
 
 OpenMP Support in Clang
 -----------------------
 
 ...
 
 CUDA Support in Clang
 ---------------------

clang/include/clang/Basic/LangOptions.h

enum class ClangABI {
     /// even when that can lead to mangling collisions.
     Ver11,
 
     /// Attempt to be ABI-compatible with code generated by Clang 12.0.x
     /// (git 8e464dd76bef). This causes clang to mangle lambdas within
     /// 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,
-
     /// Attempt to be ABI-compatible with code generated by Clang 14.0.x.
     /// This causes clang to mangle dependent nested names incorrectly.
+    /// This causes clang to pack non-POD members of packed structs.
     Ver14,
 
     /// Conform to the underlying platform's C and C++ ABIs as closely
     /// as we can.
     Latest
   };
 
   enum class CoreFoundationABI {

clang/lib/AST/RecordLayoutBuilder.cpp

void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
   uint64_t UnpaddedFieldOffset = getDataSizeInBits() - UnfilledBitsInLastUnit;
   // Reset the unfilled bits.
   UnfilledBitsInLastUnit = 0;
   LastBitfieldStorageUnitSize = 0;
 
   llvm::Triple Target = Context.getTargetInfo().getTriple();
   bool FieldPacked = (Packed && (!FieldClass || FieldClass->isPOD() ||
                                  Context.getLangOpts().getClangABICompat() <=
-                                     LangOptions::ClangABI::Ver13 ||
+                                     LangOptions::ClangABI::Ver14 ||
                                  Target.isPS4() || Target.isOSDarwin())) ||
                      D->hasAttr<PackedAttr>();
 
   AlignRequirementKind AlignRequirement = AlignRequirementKind::None;
   CharUnits FieldSize;
   CharUnits FieldAlign;
   // The amount of this class's dsize occupied by the field.
   // This is equal to FieldSize unless we're permitted to pack

clang/lib/Frontend/CompilerInvocation.cpp

#undef LANG_OPTION_WITH_MARSHALLING
   else if (Opts.getClangABICompat() == LangOptions::ClangABI::Ver7)
     GenerateArg(Args, OPT_fclang_abi_compat_EQ, "7.0", SA);
   else if (Opts.getClangABICompat() == LangOptions::ClangABI::Ver9)
     GenerateArg(Args, OPT_fclang_abi_compat_EQ, "9.0", SA);
   else if (Opts.getClangABICompat() == LangOptions::ClangABI::Ver11)
     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);
   else if (Opts.getClangABICompat() == LangOptions::ClangABI::Ver14)
     GenerateArg(Args, OPT_fclang_abi_compat_EQ, "14.0", SA);
 
   if (Opts.getSignReturnAddressScope() ==
       LangOptions::SignReturnAddressScopeKind::All)
     GenerateArg(Args, OPT_msign_return_address_EQ, "all", SA);
   else if (Opts.getSignReturnAddressScope() ==
            LangOptions::SignReturnAddressScopeKind::NonLeaf)
if (!VerParts.first.startswith("0") &&
       else if (Major <= 7)
         Opts.setClangABICompat(LangOptions::ClangABI::Ver7);
       else if (Major <= 9)
         Opts.setClangABICompat(LangOptions::ClangABI::Ver9);
       else if (Major <= 11)
         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 (Major <= 14)
         Opts.setClangABICompat(LangOptions::ClangABI::Ver14);
     } else if (Ver != "latest") {
       Diags.Report(diag::err_drv_invalid_value)
           << A->getAsString(Args) << A->getValue();
     }
   }
 

clang/test/SemaCXX/class-layout.cpp

 // 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-apple-darwin    %s -fsyntax-only -verify -std=c++11 -Wno-inaccessible-base -DCLANG_ABI_COMPAT=14
 // 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
+// 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
 // expected-no-diagnostics
 
 #define SA(n, p) int a##n[(p) ? 1 : -1]
 
 struct A {
   int a;
   char b;
 };

 };
 // 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
+#if defined(CLANG_ABI_COMPAT) && CLANG_ABI_COMPAT <= 14
 _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