[DependencyScan][Caching] Do not mix CAS instance

Make sure the CAS instances are not mixed during dependency scanning,
especially when used from libSwiftScan C APIs.

For clang scanning service and file system, it should always be created
from the global CAS instance.

For CAS instance inside the swift instance when performing dependency
scanning, it reuse the CAS instance from global as well if that is
already initialized.

rdar://173703843

lib/DependencyScan/ModuleDependencyScanner.cpp

@@ -218,6 +218,12 @@ ModuleDependencyScanningWorker::ModuleDependencyScanningWorker(
           getClangScanningFS(globalScanningService, CAS, ScanASTContext)),
       CAS(CAS), ActionCache(ActionCache),
       diagnosticReporter(DiagnosticReporter) {
+  assert(globalScanningService.ClangScanningService->getCAS() == CAS &&
+         "Need to be the same CAS instance");
+  assert(globalScanningService.ClangScanningService->getActionCache() ==
+             ActionCache &&
+         "Need to be the same ActionCache instance");
+
   // Instantiate a worker-specific diagnostic engine and copy over
   // the scanner's diagnostic consumers (expected to be thread-safe).
   workerDiagnosticEngine = std::make_unique<DiagnosticEngine>(ScanASTContext.SourceMgr);
@@ -534,7 +540,6 @@ ModuleDependencyScanner::create(SwiftDependencyScanningService &service,
       std::unique_ptr<ModuleDependencyScanner>(new ModuleDependencyScanner(
           service, cache, instance->getInvocation(), instance->getSILOptions(),
           instance->getASTContext(), *instance->getDependencyTracker(),
-          instance->getSharedCASInstance(), instance->getSharedCacheInstance(),
           instance->getDiags(),
           instance->getInvocation().getFrontendOptions().ParallelDependencyScan,
           instance->getInvocation()
@@ -560,24 +565,22 @@ ModuleDependencyScanner::ModuleDependencyScanner(
     ModuleDependenciesCache &Cache,
     const CompilerInvocation &ScanCompilerInvocation,
     const SILOptions &SILOptions, ASTContext &ScanASTContext,
-    swift::DependencyTracker &DependencyTracker,
-    std::shared_ptr<llvm::cas::ObjectStore> CAS,
-    std::shared_ptr<llvm::cas::ActionCache> ActionCache,
-    DiagnosticEngine &Diagnostics, bool ParallelScan,
-    bool EmitScanRemarks)
+    swift::DependencyTracker &DependencyTracker, DiagnosticEngine &Diagnostics,
+    bool ParallelScan, bool EmitScanRemarks)
     : ScanCompilerInvocation(ScanCompilerInvocation),
       ScanASTContext(ScanASTContext),
       ScanDiagnosticReporter(Diagnostics, EmitScanRemarks),
       ModuleOutputPath(ScanCompilerInvocation.getFrontendOptions()
-                       .ExplicitModulesOutputPath),
+                           .ExplicitModulesOutputPath),
       SDKModuleOutputPath(ScanCompilerInvocation.getFrontendOptions()
-                          .ExplicitSDKModulesOutputPath),
+                              .ExplicitSDKModulesOutputPath),
       DependencyCache(Cache),
       NumThreads(ParallelScan
                      ? llvm::hardware_concurrency().compute_thread_count()
                      : 1),
-      ScanningThreadPool(llvm::hardware_concurrency(NumThreads)), CAS(CAS),
-      ActionCache(ActionCache) {
+      ScanningThreadPool(llvm::hardware_concurrency(NumThreads)),
+      CAS(ScanningService.ClangScanningService->getCAS()),
+      ActionCache(ScanningService.ClangScanningService->getActionCache()) {
   // Setup prefix mapping.
   auto &ScannerPrefixMapper =
       ScanCompilerInvocation.getSearchPathOptions().ScannerPrefixMapper;