[clang][modules][deps] Optimize in-process timestamping of PCMs (#137363)

In the past, timestamps used for
`-fmodules-validate-once-per-build-session` were found to be a source of
contention in the dependency scanner
([D149802](https://reviews.llvm.org/D149802),
https://github.com/llvm/llvm-project/pull/112452). This PR is yet
another attempt to optimize these. We now make use of the new
`ModuleCache` interface to implement the in-process version in terms of
atomic `std::time_t` variables rather the mtime attribute on
`.timestamp` files.

1 files changed, 1 insertions, 1 deletions

diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 8c5adc3..cccf53d 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -5394,7 +5394,7 @@ ASTWriter::WriteAST(llvm::PointerUnion<Sema *, Preprocessor *> Subject,
   if (WritingModule && PPRef.getHeaderSearchInfo()
                            .getHeaderSearchOpts()
                            .ModulesValidateOncePerBuildSession)
-    updateModuleTimestamp(OutputFile);
+    ModCache.updateModuleTimestamp(OutputFile);
 
   if (ShouldCacheASTInMemory) {
     // Construct MemoryBuffer and update buffer manager.