4 files changed, 11 insertions, 2 deletions
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 3f537d21ab5..f5f96ecd24e 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -1276,7 +1276,13 @@ void ASTWriter::WritePreprocessor(const Preprocessor &PP) {
     // Don't emit builtin macros like __LINE__ to the AST file unless they have
     // been redefined by the header (in which case they are not isBuiltinMacro).
     // Also skip macros from a AST file if we're chaining.
-    if (MI->isBuiltinMacro() || (Chain && MI->isFromAST()))
+
+    // FIXME: There is a (probably minor) optimization we could do here, if
+    // the macro comes from the original PCH but the identifier comes from a
+    // chained PCH, by storing the offset into the original PCH rather than
+    // writing the macro definition a second time.
+    if (MI->isBuiltinMacro() || 
+        (Chain && I->first->isFromAST() && MI->isFromAST()))
       continue;
 
     AddIdentifierRef(I->first, Record);
diff --git a/clang/test/PCH/Inputs/chain-macro-override1.h b/clang/test/PCH/Inputs/chain-macro-override1.h
index 4f9321de93b..d956396f916 100644
--- a/clang/test/PCH/Inputs/chain-macro-override1.h
+++ b/clang/test/PCH/Inputs/chain-macro-override1.h
@@ -2,3 +2,4 @@ void f() __attribute__((unavailable));
 void g();
 #define g() f()
 #define h() f()
+#define x x
diff --git a/clang/test/PCH/Inputs/chain-macro-override2.h b/clang/test/PCH/Inputs/chain-macro-override2.h
index f279e2ad48c..e4bff77294f 100644
--- a/clang/test/PCH/Inputs/chain-macro-override2.h
+++ b/clang/test/PCH/Inputs/chain-macro-override2.h
@@ -2,3 +2,4 @@
 #undef g
 #undef h
 #define h() g()
+int x;
diff --git a/clang/test/PCH/chain-macro-override.c b/clang/test/PCH/chain-macro-override.c
index 14478af35f1..449ed8c7a0c 100644
--- a/clang/test/PCH/chain-macro-override.c
+++ b/clang/test/PCH/chain-macro-override.c
@@ -6,8 +6,9 @@
 // RUN: %clang_cc1 -emit-pch -o %t2 %S/Inputs/chain-macro-override2.h -include-pch %t1 -chained-pch
 // RUN: %clang_cc1 -include-pch %t2 -fsyntax-only -verify %s
 
-void foo() {
+int foo() {
   f();
   g();
   h();
+  return x;
 }