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
@@ -1873,6 +1873,8 @@
   PreprocessorOutputOpts<"RewriteIncludes">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option]>, NegFlag<SetFalse>>;
 
+defm directives_only : OptInCC1FFlag<"directives-only", "">;
+
 defm delete_null_pointer_checks : BoolFOption<"delete-null-pointer-checks",
   CodeGenOpts<"NullPointerIsValid">, DefaultFalse,
   NegFlag<SetTrue, [CC1Option], "Do not treat usage of null pointers as undefined behavior">,
diff --git a/clang/include/clang/Frontend/PreprocessorOutputOptions.h b/clang/include/clang/Frontend/PreprocessorOutputOptions.h
--- a/clang/include/clang/Frontend/PreprocessorOutputOptions.h
+++ b/clang/include/clang/Frontend/PreprocessorOutputOptions.h
@@ -25,6 +25,7 @@
   unsigned RewriteIncludes : 1;    ///< Preprocess include directives only.
   unsigned RewriteImports  : 1;    ///< Include contents of transitively-imported modules.
   unsigned MinimizeWhitespace : 1; ///< Ignore whitespace from input.
+  unsigned DirectivesOnly : 1; ///< Process directives but do not expand macros.
 
 public:
   PreprocessorOutputOptions() {
@@ -38,6 +39,7 @@
     RewriteIncludes = 0;
     RewriteImports = 0;
     MinimizeWhitespace = 0;
+    DirectivesOnly = 0;
   }
 };
 
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
@@ -4413,6 +4413,8 @@
     GenerateArg(Args, OPT_dM, SA);
   if (!Generate_dM && Opts.ShowMacros)
     GenerateArg(Args, OPT_dD, SA);
+  if (Opts.DirectivesOnly)
+    GenerateArg(Args, OPT_fdirectives_only, SA);
 }
 
 static bool ParsePreprocessorOutputArgs(PreprocessorOutputOptions &Opts,
@@ -4435,6 +4437,7 @@
 
   Opts.ShowCPP = isStrictlyPreprocessorAction(Action) && !Args.hasArg(OPT_dM);
   Opts.ShowMacros = Args.hasArg(OPT_dM) || Args.hasArg(OPT_dD);
+  Opts.DirectivesOnly = Args.hasArg(OPT_fdirectives_only);
 
   return Diags.getNumErrors() == NumErrorsBefore;
 }
diff --git a/clang/lib/Frontend/PrintPreprocessedOutput.cpp b/clang/lib/Frontend/PrintPreprocessedOutput.cpp
--- a/clang/lib/Frontend/PrintPreprocessedOutput.cpp
+++ b/clang/lib/Frontend/PrintPreprocessedOutput.cpp
@@ -96,6 +96,7 @@
   bool UseLineDirectives;
   bool IsFirstFileEntered;
   bool MinimizeWhitespace;
+  bool DirectivesOnly;
 
   Token PrevTok;
   Token PrevPrevTok;
@@ -103,12 +104,13 @@
 public:
   PrintPPOutputPPCallbacks(Preprocessor &pp, raw_ostream &os, bool lineMarkers,
                            bool defines, bool DumpIncludeDirectives,
-                           bool UseLineDirectives, bool MinimizeWhitespace)
+                           bool UseLineDirectives, bool MinimizeWhitespace,
+                           bool DirectivesOnly)
       : PP(pp), SM(PP.getSourceManager()), ConcatInfo(PP), OS(os),
         DisableLineMarkers(lineMarkers), DumpDefines(defines),
         DumpIncludeDirectives(DumpIncludeDirectives),
         UseLineDirectives(UseLineDirectives),
-        MinimizeWhitespace(MinimizeWhitespace) {
+        MinimizeWhitespace(MinimizeWhitespace), DirectivesOnly(DirectivesOnly) {
     CurLine = 0;
     CurFilename += "<uninit>";
     EmittedTokensOnThisLine = false;
@@ -467,12 +469,21 @@
 void PrintPPOutputPPCallbacks::MacroDefined(const Token &MacroNameTok,
                                             const MacroDirective *MD) {
   const MacroInfo *MI = MD->getMacroInfo();
-  // Only print out macro definitions in -dD mode.
-  if (!DumpDefines ||
+  // Print out macro definitions in -dD mode and when we have -fdirectives-only
+  // for C++20 header units.
+  if ((!DumpDefines && !DirectivesOnly) ||
       // Ignore __FILE__ etc.
-      MI->isBuiltinMacro()) return;
+      MI->isBuiltinMacro())
+    return;
 
-  MoveToLine(MI->getDefinitionLoc(), /*RequireStartOfLine=*/true);
+  SourceLocation DefLoc = MI->getDefinitionLoc();
+  if (DirectivesOnly && !MI->isUsed()) {
+    SourceManager &SM = PP.getSourceManager();
+    if (SM.isWrittenInBuiltinFile(DefLoc) ||
+        SM.isWrittenInCommandLineFile(DefLoc))
+      return;
+  }
+  MoveToLine(DefLoc, /*RequireStartOfLine=*/true);
   PrintMacroDefinition(*MacroNameTok.getIdentifierInfo(), *MI, PP, OS);
   setEmittedDirectiveOnThisLine();
 }
@@ -480,8 +491,10 @@
 void PrintPPOutputPPCallbacks::MacroUndefined(const Token &MacroNameTok,
                                               const MacroDefinition &MD,
                                               const MacroDirective *Undef) {
-  // Only print out macro definitions in -dD mode.
-  if (!DumpDefines) return;
+  // Print out macro definitions in -dD mode and when we have -fdirectives-only
+  // for C++20 header units.
+  if (!DumpDefines && !DirectivesOnly)
+    return;
 
   MoveToLine(MacroNameTok.getLocation(), /*RequireStartOfLine=*/true);
   OS << "#undef " << MacroNameTok.getIdentifierInfo()->getName();
@@ -959,7 +972,7 @@
   PrintPPOutputPPCallbacks *Callbacks = new PrintPPOutputPPCallbacks(
       PP, *OS, !Opts.ShowLineMarkers, Opts.ShowMacros,
       Opts.ShowIncludeDirectives, Opts.UseLineDirectives,
-      Opts.MinimizeWhitespace);
+      Opts.MinimizeWhitespace, Opts.DirectivesOnly);
 
   // Expand macros in pragmas with -fms-extensions.  The assumption is that
   // the majority of pragmas in such a file will be Microsoft pragmas.
@@ -995,6 +1008,8 @@
 
   // After we have configured the preprocessor, enter the main file.
   PP.EnterMainSourceFile();
+  if (Opts.DirectivesOnly)
+    PP.SetMacroExpansionOnlyInDirectives();
 
   // Consume all of the tokens that come from the predefines buffer.  Those
   // should not be emitted into the output and are guaranteed to be at the
diff --git a/clang/test/Modules/cxx20-hu-06.cpp b/clang/test/Modules/cxx20-hu-06.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/cxx20-hu-06.cpp
@@ -0,0 +1,68 @@
+// Test check that consuming -E -fdirectives-only output produces the expected
+// header unit.
+
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+// RUN: cd %t
+
+// RUN: %clang_cc1 -std=c++20 -E -fdirectives-only -xc++-user-header hu-01.h \
+// RUN: -o hu-01.iih
+
+// RUN: %clang_cc1 -std=c++20 -emit-header-unit \
+// RUN: -xc++-user-header-cpp-output hu-01.iih -o hu-01.pcm
+
+// RUN: %clang_cc1 -std=c++20 -emit-header-unit -xc++-user-header hu-02.h \
+// RUN: -DFOO -fmodule-file=hu-01.pcm -o hu-02.pcm -Rmodule-import 2>&1 | \
+// RUN: FileCheck --check-prefix=CHECK-IMP %s -DTDIR=%t
+
+//--- hu-01.h
+#ifndef __GUARD
+#define __GUARD
+
+int baz(int);
+#define FORTYTWO 42
+
+#define SHOULD_NOT_BE_DEFINED -1
+#undef SHOULD_NOT_BE_DEFINED
+
+#endif // __GUARD
+// expected-no-diagnostics
+
+//--- hu-02.h
+export import "hu-01.h";
+#if !defined(FORTYTWO) || FORTYTWO != 42
+#error FORTYTWO missing in hu-02
+#endif
+
+#ifndef __GUARD
+#error __GUARD missing in hu-02
+#endif
+
+#ifdef SHOULD_NOT_BE_DEFINED
+#error SHOULD_NOT_BE_DEFINED is visible
+#endif
+
+// Make sure that we have not discarded macros from the builtin file.
+#ifndef __cplusplus
+#error we dropped a defined macro
+#endif
+
+#define KAP 6174
+
+#ifdef FOO
+#define FOO_BRANCH(X) (X) + 1
+inline int foo(int x) {
+  if (x == FORTYTWO)
+    return FOO_BRANCH(x);
+  return FORTYTWO;
+}
+#else
+#define BAR_BRANCH(X) (X) + 2
+inline int bar(int x) {
+  if (x == FORTYTWO)
+    return BAR_BRANCH(x);
+  return FORTYTWO;
+}
+#endif
+// CHECK-IMP: remark: importing module './hu-01.h' from 'hu-01.pcm'