Merge pull request swiftlang#79919 from qiongsiwu/eng_145860213

[Dependency Scanning] Setting Default Clang Optimize Args Option to All

llvm/llvm-project#129809 turned off current working directory (CWD) optimization for clang dependency scanning, because clang needs to coordinate with the build system to safely optimize the CWD. Swift can already handle the CWDs. This PR turns the CWD optimization on for Swift.

Author: qiongsiwu

lib/AST/ModuleDependencies.cpp

@@ -490,7 +490,13 @@ SwiftDependencyScanningService::SwiftDependencyScanningService() {
       clang::CASOptions(),
       /* CAS (llvm::cas::ObjectStore) */ nullptr,
       /* Cache (llvm::cas::ActionCache) */ nullptr,
-      /* SharedFS */ nullptr);
+      /* SharedFS */ nullptr,
+      // ScanningOptimizations::Default excludes the current working
+      // directory optimization. Clang needs to communicate with
+      // the build system to handle the optimization safely.
+      // Swift can handle the working directory optimizaiton
+      // already so it is safe to turn on all optimizations.
+      clang::tooling::dependencies::ScanningOptimizations::All);
   SharedFilesystemCache.emplace();
 }
 
@@ -748,7 +754,11 @@ bool SwiftDependencyScanningService::setupCachingDependencyScanningService(
       ClangScanningFormat,
       Instance.getInvocation().getCASOptions().CASOpts,
       Instance.getSharedCASInstance(), Instance.getSharedCacheInstance(),
-      UseClangIncludeTree ? nullptr : CacheFS);
+      UseClangIncludeTree ? nullptr : CacheFS,
+      // The current working directory optimization (off by default)
+      // should not impact CAS. We set the optization to all to be
+      // consistent with the non-CAS case.
+      clang::tooling::dependencies::ScanningOptimizations::All);
 
   return false;
 }