Revert "[clang] Add experimental option to omit the RTTI component from the vtable when -fno-rtti is used"

This reverts commit 6385c1d.

Reverting since this broke a windows builder:
https://lab.llvm.org/buildbot/#/builders/216/builds/27252.

Author: PiJoules

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -674,9 +674,6 @@ def err_cc1_round_trip_mismatch : Error<
 def err_cc1_unbounded_vscale_min : Error<
   "minimum vscale must be an unsigned integer greater than 0">;
 
-def err_drv_using_omit_rtti_component_without_no_rtti : Error<
-  "-fexperimental-omit-vtable-rtti call only be used with -fno-rtti">;
-
 def err_drv_ssp_missing_offset_argument : Error<
   "'%0' is used without '-mstack-protector-guard-offset', and there is no default">;
 

clang/include/clang/Basic/LangOptions.def

@@ -450,9 +450,6 @@ LANGOPT(SpeculativeLoadHardening, 1, 0, "Speculative load hardening enabled")
 LANGOPT(RelativeCXXABIVTables, 1, 0,
         "Use an ABI-incompatible v-table layout that uses relative references")
 
-LANGOPT(OmitVTableRTTI, 1, 0,
-        "Use an ABI-incompatible v-table layout that omits the RTTI component")
-
 LANGOPT(VScaleMin, 32, 0, "Minimum vscale value")
 LANGOPT(VScaleMax, 32, 0, "Maximum vscale value")
 

clang/include/clang/Driver/Options.td

@@ -2671,12 +2671,6 @@ def fno_experimental_relative_cxx_abi_vtables :
   Group<f_clang_Group>, Visibility<[ClangOption, CC1Option]>,
   HelpText<"Do not use the experimental C++ class ABI for classes with virtual tables">;
 
-defm experimental_omit_vtable_rtti : BoolFOption<"experimental-omit-vtable-rtti",
-  LangOpts<"OmitVTableRTTI">, DefaultFalse,
-  PosFlag<SetTrue, [], [CC1Option], "Omit">,
-  NegFlag<SetFalse, [], [CC1Option], "Do not omit">,
-  BothFlags<[], [CC1Option], " the RTTI component from virtual tables">>;
-
 def fcxx_abi_EQ : Joined<["-"], "fc++-abi=">,
                   Group<f_clang_Group>, Visibility<[ClangOption, CC1Option]>,
                   HelpText<"C++ ABI to use. This will override the target C++ ABI.">;

clang/lib/AST/VTableBuilder.cpp

@@ -665,11 +665,7 @@ CharUnits VCallAndVBaseOffsetBuilder::getCurrentOffsetOffset() const {
   // vtable address point. (We subtract 3 to account for the information just
   // above the address point, the RTTI info, the offset to top, and the
   // vcall offset itself).
-  size_t NumComponentsAboveAddrPoint = 3;
-  if (Context.getLangOpts().OmitVTableRTTI)
-    NumComponentsAboveAddrPoint--;
-  int64_t OffsetIndex =
-      -(int64_t)(NumComponentsAboveAddrPoint + Components.size());
+  int64_t OffsetIndex = -(int64_t)(3 + Components.size());
 
   // Under the relative ABI, the offset widths are 32-bit ints instead of
   // pointer widths.
@@ -1673,8 +1669,7 @@ void ItaniumVTableBuilder::LayoutPrimaryAndSecondaryVTables(
   Components.push_back(VTableComponent::MakeOffsetToTop(OffsetToTop));
 
   // Next, add the RTTI.
-  if (!Context.getLangOpts().OmitVTableRTTI)
-    Components.push_back(VTableComponent::MakeRTTI(MostDerivedClass));
+  Components.push_back(VTableComponent::MakeRTTI(MostDerivedClass));
 
   uint64_t AddressPoint = Components.size();
 

clang/lib/Driver/ToolChains/Clang.cpp

@@ -5526,9 +5526,6 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   Args.AddLastArg(CmdArgs, options::OPT_fexperimental_relative_cxx_abi_vtables,
                   options::OPT_fno_experimental_relative_cxx_abi_vtables);
 
-  Args.AddLastArg(CmdArgs, options::OPT_fexperimental_omit_vtable_rtti,
-                  options::OPT_fno_experimental_omit_vtable_rtti);
-
   // Handle segmented stacks.
   Args.addOptInFlag(CmdArgs, options::OPT_fsplit_stack,
                     options::OPT_fno_split_stack);
@@ -6010,9 +6007,6 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   Args.AddLastArg(CmdArgs, options::OPT_fexperimental_relative_cxx_abi_vtables,
                   options::OPT_fno_experimental_relative_cxx_abi_vtables);
 
-  Args.AddLastArg(CmdArgs, options::OPT_fexperimental_omit_vtable_rtti,
-                  options::OPT_fno_experimental_omit_vtable_rtti);
-
   if (Arg *A = Args.getLastArg(options::OPT_ffuchsia_api_level_EQ))
     A->render(Args, CmdArgs);
 

clang/lib/Frontend/CompilerInvocation.cpp

@@ -4109,14 +4109,6 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
                    options::OPT_fno_experimental_relative_cxx_abi_vtables,
                    TargetCXXABI::usesRelativeVTables(T));
 
-  // RTTI is on by default.
-  bool HasRTTI = Args.hasFlag(options::OPT_frtti, options::OPT_fno_rtti, true);
-  Opts.OmitVTableRTTI =
-      Args.hasFlag(options::OPT_fexperimental_omit_vtable_rtti,
-                   options::OPT_fno_experimental_omit_vtable_rtti, false);
-  if (Opts.OmitVTableRTTI && HasRTTI)
-    Diags.Report(diag::err_drv_using_omit_rtti_component_without_no_rtti);
-
   for (const auto &A : Args.getAllArgValues(OPT_fmacro_prefix_map_EQ)) {
     auto Split = StringRef(A).split('=');
     Opts.MacroPrefixMap.insert(