Index: clang/include/clang/Lex/Preprocessor.h
===================================================================
--- clang/include/clang/Lex/Preprocessor.h
+++ clang/include/clang/Lex/Preprocessor.h
@@ -1773,17 +1773,6 @@
   /// CurTokenLexer pointers.
   void recomputeCurLexerKind();
 
-  /// Returns true if incremental processing is enabled
-  bool isIncrementalProcessingEnabled() const {
-    return getLangOpts().IncrementalExtensions;
-  }
-
-  /// Enables the incremental processing
-  void enableIncrementalProcessing(bool value = true) {
-    // FIXME: Drop this interface.
-    const_cast<LangOptions &>(getLangOpts()).IncrementalExtensions = value;
-  }
-
   /// Specify the point at which code-completion will be performed.
   ///
   /// \param File the file in which code completion should occur. If
Index: clang/lib/Interpreter/IncrementalParser.cpp
===================================================================
--- clang/lib/Interpreter/IncrementalParser.cpp
+++ clang/lib/Interpreter/IncrementalParser.cpp
@@ -216,7 +216,7 @@
 llvm::Expected<PartialTranslationUnit &>
 IncrementalParser::Parse(llvm::StringRef input) {
   Preprocessor &PP = CI->getPreprocessor();
-  assert(PP.isIncrementalProcessingEnabled() && "Not in incremental mode!?");
+  assert(PP.getLangOpts().IncrementalExtensions && "Not in incremental mode!?");
 
   std::ostringstream SourceName;
   SourceName << "input_line_" << InputCount++;
Index: clang/lib/Lex/PPLexerChange.cpp
===================================================================
--- clang/lib/Lex/PPLexerChange.cpp
+++ clang/lib/Lex/PPLexerChange.cpp
@@ -550,12 +550,11 @@
         << PPOpts->PCHThroughHeader << 0;
   }
 
-  if (!isIncrementalProcessingEnabled())
+  if (!getLangOpts().IncrementalExtensions) {
     // We're done with lexing.
     CurLexer.reset();
-
-  if (!isIncrementalProcessingEnabled())
     CurPPLexer = nullptr;
+  }
 
   if (TUKind == TU_Complete) {
     // This is the end of the top-level file. 'WarnUnusedMacroLocs' has
Index: clang/lib/Parse/ParseDecl.cpp
===================================================================
--- clang/lib/Parse/ParseDecl.cpp
+++ clang/lib/Parse/ParseDecl.cpp
@@ -5382,7 +5382,7 @@
 }
 
 Parser::DeclGroupPtrTy Parser::ParseTopLevelStmtDecl() {
-  assert(PP.isIncrementalProcessingEnabled() && "Not in incremental mode");
+  assert(PP.getLangOpts().IncrementalExtensions && "Not in incremental mode");
 
   // Parse a top-level-stmt.
   Parser::StmtVector Stmts;
Index: clang/lib/Parse/Parser.cpp
===================================================================
--- clang/lib/Parse/Parser.cpp
+++ clang/lib/Parse/Parser.cpp
@@ -614,7 +614,7 @@
 
   // Skip over the EOF token, flagging end of previous input for incremental
   // processing
-  if (PP.isIncrementalProcessingEnabled() && Tok.is(tok::eof))
+  if (PP.getLangOpts().IncrementalExtensions && Tok.is(tok::eof))
     ConsumeToken();
 
   Result = nullptr;
@@ -1028,7 +1028,7 @@
       ConsumeToken();
       return nullptr;
     }
-    if (PP.isIncrementalProcessingEnabled() &&
+    if (PP.getLangOpts().IncrementalExtensions &&
         !isDeclarationStatement(/*DisambiguatingWithExpression=*/true))
       return ParseTopLevelStmtDecl();
 
Index: clang/lib/Sema/Sema.cpp
===================================================================
--- clang/lib/Sema/Sema.cpp
+++ clang/lib/Sema/Sema.cpp
@@ -1166,9 +1166,9 @@
                      }),
       UnusedFileScopedDecls.end());
 
+  // Translation unit prefixes don't need any of the checking below.
   if (TUKind == TU_Prefix) {
-    // Translation unit prefixes don't need any of the checking below.
-    if (!PP.isIncrementalProcessingEnabled())
+    if (!LangOpts.IncrementalExtensions)
       TUScope = nullptr;
     return;
   }
@@ -1435,7 +1435,7 @@
   assert(ParsingInitForAutoVars.empty() &&
          "Didn't unmark var as having its initializer parsed");
 
-  if (!PP.isIncrementalProcessingEnabled())
+  if (TUKind != TU_Incremental)
     TUScope = nullptr;
 }
 
Index: clang/unittests/Frontend/FrontendActionTest.cpp
===================================================================
--- clang/unittests/Frontend/FrontendActionTest.cpp
+++ clang/unittests/Frontend/FrontendActionTest.cpp
@@ -30,22 +30,12 @@
 
 class TestASTFrontendAction : public ASTFrontendAction {
 public:
-  TestASTFrontendAction(bool enableIncrementalProcessing = false,
-                        bool actOnEndOfTranslationUnit = false)
-    : EnableIncrementalProcessing(enableIncrementalProcessing),
-      ActOnEndOfTranslationUnit(actOnEndOfTranslationUnit) { }
+  TestASTFrontendAction(bool actOnEndOfTranslationUnit = false)
+      : ActOnEndOfTranslationUnit(actOnEndOfTranslationUnit) {}
 
-  bool EnableIncrementalProcessing;
   bool ActOnEndOfTranslationUnit;
   std::vector<std::string> decl_names;
 
-  bool BeginSourceFileAction(CompilerInstance &ci) override {
-    if (EnableIncrementalProcessing)
-      ci.getPreprocessor().enableIncrementalProcessing();
-
-    return ASTFrontendAction::BeginSourceFileAction(ci);
-  }
-
   std::unique_ptr<ASTConsumer> CreateASTConsumer(CompilerInstance &CI,
                                                  StringRef InFile) override {
     return std::make_unique<Visitor>(CI, ActOnEndOfTranslationUnit,
@@ -108,11 +98,12 @@
       FrontendInputFile("test.cc", Language::CXX));
   invocation->getFrontendOpts().ProgramAction = frontend::ParseSyntaxOnly;
   invocation->getTargetOpts().Triple = "i386-unknown-linux-gnu";
+  invocation->getLangOpts()->IncrementalExtensions = 1;
   CompilerInstance compiler;
   compiler.setInvocation(std::move(invocation));
   compiler.createDiagnostics();
 
-  TestASTFrontendAction test_action(/*enableIncrementalProcessing=*/true);
+  TestASTFrontendAction test_action;
   ASSERT_TRUE(compiler.ExecuteAction(test_action));
   ASSERT_EQ(2U, test_action.decl_names.size());
   EXPECT_EQ("main", test_action.decl_names[0]);
@@ -123,6 +114,7 @@
   auto invocation = std::make_shared<CompilerInvocation>();
   invocation->getLangOpts()->CPlusPlus = true;
   invocation->getLangOpts()->DelayedTemplateParsing = true;
+  invocation->getLangOpts()->IncrementalExtensions = 1;
   invocation->getPreprocessorOpts().addRemappedFile(
     "test.cc", MemoryBuffer::getMemBuffer(
       "template<typename T> struct A { A(T); T data; };\n"
@@ -139,8 +131,7 @@
   compiler.setInvocation(std::move(invocation));
   compiler.createDiagnostics();
 
-  TestASTFrontendAction test_action(/*enableIncrementalProcessing=*/true,
-                                    /*actOnEndOfTranslationUnit=*/true);
+  TestASTFrontendAction test_action(/*actOnEndOfTranslationUnit=*/true);
   ASSERT_TRUE(compiler.ExecuteAction(test_action));
   ASSERT_EQ(13U, test_action.decl_names.size());
   EXPECT_EQ("A", test_action.decl_names[0]);
Index: lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp
===================================================================
--- lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp
+++ lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp
@@ -609,7 +609,8 @@
       "-target",
       arch.GetTriple().str(),
       "-fmodules-validate-system-headers",
-      "-Werror=non-modular-include-in-framework-module"};
+      "-Werror=non-modular-include-in-framework-module",
+      "-Xclang=-fincremental-extensions"};
 
   target.GetPlatform()->AddClangModuleCompilationOptions(
       &target, compiler_invocation_arguments);
@@ -701,8 +702,6 @@
                                instance->getFrontendOpts().Inputs[0]))
     return nullptr;
 
-  instance->getPreprocessor().enableIncrementalProcessing();
-
   instance->createASTReader();
 
   instance->createSema(action->getTranslationUnitKind(), nullptr);