diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -434,8 +434,11 @@
     AutoNormalizeEnum {}
 
 // Key paths that are constant during parsing of options with the same key path prefix.
+defvar cplusplus = LangOpts<"CPlusPlus">;
+defvar c99 = LangOpts<"C99">;
 defvar lang_std = LangOpts<"LangStd">;
 defvar open_cl = LangOpts<"OpenCL">;
+defvar gnu_mode = LangOpts<"GNUMode">;
 
 defvar std = !strconcat("LangStandard::getLangStandardForKind(", lang_std.KeyPath, ")");
 
@@ -1619,9 +1622,19 @@
 def fgnuc_version_EQ : Joined<["-"], "fgnuc-version=">, Group<f_Group>,
   HelpText<"Sets various macros to claim compatibility with the given GCC version (default is 4.2.1)">,
   Flags<[CC1Option, CoreOption]>;
-def fgnu_keywords : Flag<["-"], "fgnu-keywords">, Group<f_Group>, Flags<[CC1Option]>,
-  HelpText<"Allow GNU-extension keywords regardless of language standard">;
-defm gnu89_inline : OptInFFlag<"gnu89-inline", "Use the gnu89 inline semantics">;
+// We abuse '-f[no-]gnu-keywords' to force overriding all GNU-extension
+// keywords. This behavior is provided by GCC's poorly named '-fasm' flag,
+// while a subset (the non-C++ GNU keywords) is provided by GCC's
+// '-fgnu-keywords'. Clang conflates the two for simplicity under the single
+// name, as it doesn't seem a useful distinction.
+defm gnu_keywords : BoolFOption<"gnu-keywords",
+  LangOpts<"GNUKeywords">, Default<gnu_mode.KeyPath>,
+  PosFlag<SetTrue, [], "Allow GNU-extension keywords regardless of language standard">,
+  NegFlag<SetFalse>, BothFlags<[CC1Option]>>;
+defm gnu89_inline : BoolFOption<"gnu89-inline",
+  LangOpts<"GNUInline">, Default<!strconcat("!", c99.KeyPath, " && !", cplusplus.KeyPath)>,
+  PosFlag<SetTrue, [CC1Option], "Use the gnu89 inline semantics">,
+  NegFlag<SetFalse>>, ShouldParseIf<!strconcat("!", cplusplus.KeyPath)>;
 def fgnu_runtime : Flag<["-"], "fgnu-runtime">, Group<f_Group>,
   HelpText<"Generate output compatible with the standard GNU Objective-C runtime">;
 def fheinous_gnu_extensions : Flag<["-"], "fheinous-gnu-extensions">, Flags<[CC1Option]>,
@@ -1965,7 +1978,6 @@
 def fno_dollars_in_identifiers : Flag<["-"], "fno-dollars-in-identifiers">, Group<f_Group>,
   HelpText<"Disallow '$' in identifiers">, Flags<[CC1Option]>;
 def fno_eliminate_unused_debug_symbols : Flag<["-"], "fno-eliminate-unused-debug-symbols">, Group<f_Group>;
-def fno_gnu_keywords : Flag<["-"], "fno-gnu-keywords">, Group<f_Group>, Flags<[CC1Option]>;
 def fno_inline_functions : Flag<["-"], "fno-inline-functions">, Group<f_clang_Group>, Flags<[CC1Option]>;
 def fno_inline : Flag<["-"], "fno-inline">, Group<f_clang_Group>, Flags<[CC1Option]>;
 def fno_global_isel : Flag<["-"], "fno-global-isel">, Group<f_clang_Group>,
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -400,9 +400,11 @@
             MERGER(KEYPATH, static_cast<decltype(KEYPATH)>(*MaybeValue));      \
   }
 
+static const StringRef GetInputKindName(InputKind IK);
+
 static void FixupInvocation(CompilerInvocation &Invocation,
-                            DiagnosticsEngine &Diags,
-                            const InputArgList &Args) {
+                            DiagnosticsEngine &Diags, const InputArgList &Args,
+                            InputKind IK) {
   LangOptions &LangOpts = *Invocation.getLangOpts();
   CodeGenOptions &CodeGenOpts = Invocation.getCodeGenOpts();
   TargetOptions &TargetOpts = Invocation.getTargetOpts();
@@ -438,6 +440,10 @@
     LangOpts.NewAlignOverride = 0;
   }
 
+  if (Args.hasArg(OPT_fgnu89_inline) && LangOpts.CPlusPlus)
+    Diags.Report(diag::err_drv_argument_not_allowed_with)
+        << "-fgnu89-inline" << GetInputKindName(IK);
+
   if (Arg *A = Args.getLastArg(OPT_fdefault_calling_conv_EQ)) {
     auto DefaultCC = LangOpts.getDefaultCallingConv();
 
@@ -1984,7 +1990,6 @@
   Opts.CPlusPlus20 = Std.isCPlusPlus20();
   Opts.CPlusPlus2b = Std.isCPlusPlus2b();
   Opts.GNUMode = Std.isGNUMode();
-  Opts.GNUInline = !Opts.C99 && !Opts.CPlusPlus;
   Opts.GNUCVersion = 0;
   Opts.HexFloats = Std.hasHexFloats();
   Opts.ImplicitInt = Std.hasImplicitInt();
@@ -2056,7 +2061,6 @@
   // C++ has wchar_t keyword.
   Opts.WChar = Opts.CPlusPlus;
 
-  Opts.GNUKeywords = Opts.GNUMode;
   Opts.CXXOperatorNames = Opts.CPlusPlus;
 
   Opts.AlignedAllocation = Opts.CPlusPlus17;
@@ -2254,14 +2258,6 @@
         << Args.getLastArg(OPT_cl_strict_aliasing)->getAsString(Args);
   }
 
-  // We abuse '-f[no-]gnu-keywords' to force overriding all GNU-extension
-  // keywords. This behavior is provided by GCC's poorly named '-fasm' flag,
-  // while a subset (the non-C++ GNU keywords) is provided by GCC's
-  // '-fgnu-keywords'. Clang conflates the two for simplicity under the single
-  // name, as it doesn't seem a useful distinction.
-  Opts.GNUKeywords = Args.hasFlag(OPT_fgnu_keywords, OPT_fno_gnu_keywords,
-                                  Opts.GNUKeywords);
-
   if (Args.hasArg(OPT_fno_operator_names))
     Opts.CXXOperatorNames = 0;
 
@@ -2344,14 +2340,6 @@
     Opts.GNUCVersion = Major * 100 * 100 + Minor * 100 + Patch;
   }
 
-  if (Args.hasArg(OPT_fgnu89_inline)) {
-    if (Opts.CPlusPlus)
-      Diags.Report(diag::err_drv_argument_not_allowed_with)
-        << "-fgnu89-inline" << GetInputKindName(IK);
-    else
-      Opts.GNUInline = 1;
-  }
-
   if (Args.hasArg(OPT_ftrapv)) {
     Opts.setSignedOverflowBehavior(LangOptions::SOB_Trapping);
     // Set the handler, if one is specified.
@@ -2994,7 +2982,7 @@
   Res.getCodeGenOpts().Argv0 = Argv0;
   Res.getCodeGenOpts().CommandLineArgs = CommandLineArgs;
 
-  FixupInvocation(Res, Diags, Args);
+  FixupInvocation(Res, Diags, Args, DashX);
 
   return Success;
 }