Index: clang/include/clang/Tooling/DependencyScanning/DependencyScanningService.h
===================================================================
--- clang/include/clang/Tooling/DependencyScanning/DependencyScanningService.h
+++ clang/include/clang/Tooling/DependencyScanning/DependencyScanningService.h
@@ -48,7 +48,8 @@
 public:
   DependencyScanningService(ScanningMode Mode, ScanningOutputFormat Format,
                             bool ReuseFileManager = true,
-                            bool SkipExcludedPPRanges = true);
+                            bool SkipExcludedPPRanges = true,
+                            bool InterceptModuleOutputs = true);
 
   ScanningMode getMode() const { return Mode; }
 
@@ -56,6 +57,8 @@
 
   bool canReuseFileManager() const { return ReuseFileManager; }
 
+  bool interceptModuleOutputs() const { return InterceptModuleOutputs; }
+
   bool canSkipExcludedPPRanges() const { return SkipExcludedPPRanges; }
 
   DependencyScanningFilesystemSharedCache &getSharedCache() {
@@ -70,6 +73,8 @@
   /// ranges by bumping the buffer pointer in the lexer instead of lexing the
   /// tokens in the range until reaching the corresponding directive.
   const bool SkipExcludedPPRanges;
+  /// Whether to intercept modules in-memory to avoid disk traffic.
+  const bool InterceptModuleOutputs;
   /// The global file system cache.
   DependencyScanningFilesystemSharedCache SharedCache;
 };
Index: clang/include/clang/Tooling/DependencyScanning/DependencyScanningWorker.h
===================================================================
--- clang/include/clang/Tooling/DependencyScanning/DependencyScanningWorker.h
+++ clang/include/clang/Tooling/DependencyScanning/DependencyScanningWorker.h
@@ -19,6 +19,7 @@
 #include "clang/Tooling/DependencyScanning/ModuleDepCollector.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/OutputManager.h"
 #include <string>
 
 namespace clang {
@@ -68,6 +69,9 @@
   std::shared_ptr<PCHContainerOperations> PCHContainerOps;
   std::unique_ptr<ExcludedPreprocessorDirectiveSkipMapping> PPSkipMappings;
 
+  /// Output manager to use.
+  std::shared_ptr<llvm::vfs::OutputManager> Outputs;
+
   llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> RealFS;
   /// The file system that is used by each worker when scanning for
   /// dependencies. This filesystem persists accross multiple compiler
Index: clang/lib/Tooling/DependencyScanning/DependencyScanningService.cpp
===================================================================
--- clang/lib/Tooling/DependencyScanning/DependencyScanningService.cpp
+++ clang/lib/Tooling/DependencyScanning/DependencyScanningService.cpp
@@ -14,6 +14,7 @@
 
 DependencyScanningService::DependencyScanningService(
     ScanningMode Mode, ScanningOutputFormat Format, bool ReuseFileManager,
-    bool SkipExcludedPPRanges)
+    bool SkipExcludedPPRanges, bool InterceptModuleOutputs)
     : Mode(Mode), Format(Format), ReuseFileManager(ReuseFileManager),
-      SkipExcludedPPRanges(SkipExcludedPPRanges) {}
+      SkipExcludedPPRanges(SkipExcludedPPRanges),
+      InterceptModuleOutputs(InterceptModuleOutputs) {}
Index: clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp
===================================================================
--- clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp
+++ clang/lib/Tooling/DependencyScanning/DependencyScanningWorker.cpp
@@ -50,12 +50,13 @@
 public:
   DependencyScanningAction(
       StringRef WorkingDirectory, DependencyConsumer &Consumer,
+      std::shared_ptr<llvm::vfs::OutputManager> Outputs,
       llvm::IntrusiveRefCntPtr<DependencyScanningWorkerFilesystem> DepFS,
       ExcludedPreprocessorDirectiveSkipMapping *PPSkipMappings,
       ScanningOutputFormat Format)
       : WorkingDirectory(WorkingDirectory), Consumer(Consumer),
-        DepFS(std::move(DepFS)), PPSkipMappings(PPSkipMappings),
-        Format(Format) {}
+        Outputs(std::move(Outputs)), DepFS(std::move(DepFS)),
+        PPSkipMappings(PPSkipMappings), Format(Format) {}
 
   bool runInvocation(std::shared_ptr<CompilerInvocation> Invocation,
                      FileManager *FileMgr,
@@ -65,6 +66,14 @@
     CompilerInstance Compiler(std::move(PCHContainerOps));
     Compiler.setInvocation(std::move(Invocation));
 
+    // Configure the output manager.
+    if (Outputs) {
+      Compiler.setOutputManager(std::move(Outputs));
+
+      // FIXME: Is this the best way to set the flag?
+      Compiler.getFrontendOpts().BuildingImplicitModuleUsesLock = false;
+    }
+
     // Don't print 'X warnings and Y errors generated'.
     Compiler.getDiagnosticOpts().ShowCarets = false;
     // Create the compiler's actual diagnostics engine.
@@ -142,6 +151,7 @@
 private:
   StringRef WorkingDirectory;
   DependencyConsumer &Consumer;
+  std::shared_ptr<llvm::vfs::OutputManager> Outputs;
   llvm::IntrusiveRefCntPtr<DependencyScanningWorkerFilesystem> DepFS;
   ExcludedPreprocessorDirectiveSkipMapping *PPSkipMappings;
   ScanningOutputFormat Format;
@@ -155,6 +165,35 @@
   DiagOpts = new DiagnosticOptions();
   PCHContainerOps = std::make_shared<PCHContainerOperations>();
   RealFS = llvm::vfs::createPhysicalFileSystem();
+
+  if (Service.interceptModuleOutputs()) {
+    using namespace llvm;
+    using namespace llvm::vfs;
+
+    // Create an in-memory filesystem for storing modules and overlay it on top
+    // of RealFS.
+    auto InMemoryFS = makeIntrusiveRefCnt<InMemoryFileSystem>();
+    {
+      auto OverlayFS =
+        makeIntrusiveRefCnt<OverlayFileSystem>(createPhysicalFileSystem());
+      OverlayFS->pushOverlay(InMemoryFS);
+      RealFS = std::move(OverlayFS);
+    }
+
+    // Capture outputs with a ".pcm" extension and save them in ModulesCache.
+    // Don't reject attempts to overwrite (it'll still reject if the content
+    // doesn't match).
+    //
+    // FIXME: The workers could share a single cache using an in-memory CAS.
+    auto InMemoryOutputs =
+        makeIntrusiveRefCnt<InMemoryOutputBackend>(std::move(InMemoryFS));
+    InMemoryOutputs->setShouldRejectExistingFiles(false);
+    Outputs = std::make_shared<OutputManager>(makeFilteringOutputBackend(
+        std::move(InMemoryOutputs), [](StringRef OutputPath, OutputConfig) {
+          return llvm::sys::path::extension(OutputPath) == ".pcm";
+        }));
+  }
+
   if (Service.canSkipExcludedPPRanges())
     PPSkipMappings =
         std::make_unique<ExcludedPreprocessorDirectiveSkipMapping>();
@@ -193,7 +232,7 @@
     Tool.setRestoreWorkingDir(false);
     Tool.setPrintErrorMessage(false);
     Tool.setDiagnosticConsumer(&DC);
-    DependencyScanningAction Action(WorkingDirectory, Consumer, DepFS,
+    DependencyScanningAction Action(WorkingDirectory, Consumer, Outputs, DepFS,
                                     PPSkipMappings.get(), Format);
     return !Tool.run(&Action);
   });
Index: clang/tools/clang-scan-deps/ClangScanDeps.cpp
===================================================================
--- clang/tools/clang-scan-deps/ClangScanDeps.cpp
+++ clang/tools/clang-scan-deps/ClangScanDeps.cpp
@@ -160,6 +160,12 @@
         "until reaching the end directive."),
     llvm::cl::init(true), llvm::cl::cat(DependencyScannerCategory));
 
+llvm::cl::opt<bool> InterceptModuleOutputs(
+    "intercept-module-outputs",
+    llvm::cl::desc(
+        "Keep the module outputs in-memory only, skipping the on-disk cache."),
+    llvm::cl::init(true), llvm::cl::cat(DependencyScannerCategory));
+
 llvm::cl::opt<bool> Verbose("v", llvm::cl::Optional,
                             llvm::cl::desc("Use verbose output."),
                             llvm::cl::init(false),
@@ -485,7 +491,8 @@
   SharedStream DependencyOS(llvm::outs());
 
   DependencyScanningService Service(ScanMode, Format, ReuseFileManager,
-                                    SkipExcludedPPRanges);
+                                    SkipExcludedPPRanges,
+                                    InterceptModuleOutputs);
   llvm::ThreadPool Pool(llvm::hardware_concurrency(NumThreads));
   std::vector<std::unique_ptr<DependencyScanningTool>> WorkerTools;
   for (unsigned I = 0; I < Pool.getThreadCount(); ++I)