From 5abcc242a65b4968cfbd706705c611b691f196ab Mon Sep 17 00:00:00 2001
From: Qiongsi Wu <qiongsi_wu@apple.com>
Date: Fri, 1 Aug 2025 14:03:25 -0700
Subject: [PATCH] Move the code to update timestamp later to avoid updating
 timestamp before the pcm is committed to disk.

---
 clang/lib/Frontend/CompilerInstance.cpp | 8 ++++++++
 clang/lib/Serialization/ASTWriter.cpp   | 5 -----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index ed6a651d919a1..ae285b117f5e0 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -1480,6 +1480,14 @@ static bool compileModuleAndReadASTImpl(CompilerInstance &ImportingInstance,
     return false;
   }
 
+  // The module is built successfully, we can update its timestamp now.
+  if (ImportingInstance.getPreprocessor()
+          .getHeaderSearchInfo()
+          .getHeaderSearchOpts()
+          .ModulesValidateOncePerBuildSession) {
+    ImportingInstance.getModuleCache().updateModuleTimestamp(ModuleFileName);
+  }
+
   return readASTAfterCompileModule(ImportingInstance, ImportLoc, ModuleNameLoc,
                                    Module, ModuleFileName,
                                    /*OutOfDate=*/nullptr, /*Missing=*/nullptr);
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index a6957e54b66f1..0c7ddd07553a4 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -5461,11 +5461,6 @@ ASTWriter::WriteAST(llvm::PointerUnion<Sema *, Preprocessor *> Subject,
 
   WritingAST = false;
 
-  if (WritingModule && PPRef.getHeaderSearchInfo()
-                           .getHeaderSearchOpts()
-                           .ModulesValidateOncePerBuildSession)
-    ModCache.updateModuleTimestamp(OutputFile);
-
   if (ShouldCacheASTInMemory) {
     // Construct MemoryBuffer and update buffer manager.
     ModCache.getInMemoryModuleCache().addBuiltPCM(