[clang][cli] Parse & generate options necessary for LangOptions defaults manually

It turns out we need to handle `LangOptions` separately from the rest of the options. `LangOptions` used to be conditionally parsed only when `!(DashX.getFormat() == InputKind::Precompiled || DashX.getLanguage() == Language::LLVM_IR)` and we need to restore this order (for more info, see D94682).

D94682 moves the parsing of marshalled `LangOpts` from `parseSimpleArgs` back to `ParseLangArgs`.

We need to parse marshalled `LangOpts` **after** `ParseLangArgs` calls `setLangDefaults`. This will enable future patches, where values of some `LangOpts` depend on the defaults.

However, two language options (`-finclude-default-header` and `-fdeclare-opencl-builtins`) need to be parsed **before** `ParseLangArgs` calls `setLangDefaults`, because they are necessary for setting up OpenCL defaults correctly.
This patch implements this by removing their marshalling info and manually parsing (and generating) them exactly where necessary.

Reviewed By: Bigcheese

Differential Revision: https://reviews.llvm.org/D94678

Author: jansvoboda11

clang/include/clang/Driver/Options.td

@@ -5207,12 +5207,13 @@ def fdefault_calling_conv_EQ : Joined<["-"], "fdefault-calling-conv=">,
   NormalizedValuesScope<"LangOptions">,
   NormalizedValues<["DCC_CDecl", "DCC_FastCall", "DCC_StdCall", "DCC_VectorCall", "DCC_RegCall"]>,
   MarshallingInfoString<LangOpts<"DefaultCallingConv">, "DCC_None">, AutoNormalizeEnum;
+
+// These options cannot be marshalled, because they are used to set up the LangOptions defaults.
 def finclude_default_header : Flag<["-"], "finclude-default-header">,
-  HelpText<"Include default header file for OpenCL">,
-  MarshallingInfoFlag<LangOpts<"IncludeDefaultHeader">>;
+  HelpText<"Include default header file for OpenCL">;
 def fdeclare_opencl_builtins : Flag<["-"], "fdeclare-opencl-builtins">,
-  HelpText<"Add OpenCL builtin function declarations (experimental)">,
-  MarshallingInfoFlag<LangOpts<"DeclareOpenCLBuiltins">>;
+  HelpText<"Add OpenCL builtin function declarations (experimental)">;
+
 def fpreserve_vec3_type : Flag<["-"], "fpreserve-vec3-type">,
   HelpText<"Preserve 3-component vector type">,
   MarshallingInfoFlag<CodeGenOpts<"PreserveVec3Type">>;

clang/lib/Frontend/CompilerInvocation.cpp

@@ -491,6 +491,11 @@ static unsigned getOptimizationLevelSize(ArgList &Args) {
   return 0;
 }
 
+static std::string GetOptName(llvm::opt::OptSpecifier OptSpecifier) {
+  static const OptTable &OptTable = getDriverOptTable();
+  return OptTable.getOption(OptSpecifier).getPrefixedName();
+}
+
 static void addDiagnosticArgs(ArgList &Args, OptSpecifier Group,
                               OptSpecifier GroupWithValue,
                               std::vector<std::string> &Diagnostics) {
@@ -2137,6 +2142,15 @@ static const StringRef GetInputKindName(InputKind IK) {
   llvm_unreachable("unknown input language");
 }
 
+static void GenerateLangArgs(const LangOptions &Opts,
+                             SmallVectorImpl<const char *> &Args,
+                             CompilerInvocation::StringAllocator SA) {
+  if (Opts.IncludeDefaultHeader)
+    Args.push_back(SA(GetOptName(OPT_finclude_default_header)));
+  if (Opts.DeclareOpenCLBuiltins)
+    Args.push_back(SA(GetOptName(OPT_fdeclare_opencl_builtins)));
+}
+
 static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
                           const llvm::Triple &T,
                           std::vector<std::string> &Includes,
@@ -2212,6 +2226,10 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
 
   Opts.SYCLIsDevice = Opts.SYCL && Args.hasArg(options::OPT_fsycl_is_device);
 
+  // These need to be parsed now. They are used to set OpenCL defaults.
+  Opts.IncludeDefaultHeader = Args.hasArg(OPT_finclude_default_header);
+  Opts.DeclareOpenCLBuiltins = Args.hasArg(OPT_fdeclare_opencl_builtins);
+
   CompilerInvocation::setLangDefaults(Opts, IK, T, Includes, LangStd);
 
   // -cl-strict-aliasing needs to emit diagnostic in the case where CL > 1.0.
@@ -3163,6 +3181,8 @@ void CompilerInvocation::generateCC1CommandLine(
 #undef DIAG_OPTION_WITH_MARSHALLING
 #undef OPTION_WITH_MARSHALLING
 #undef GENERATE_OPTION_WITH_MARSHALLING
+
+  GenerateLangArgs(*LangOpts, Args, SA);
 }
 
 IntrusiveRefCntPtr<llvm::vfs::FileSystem>