Index: clang-tools-extra/clang-tidy/ExpandModularHeadersPPCallbacks.cpp
===================================================================
--- clang-tools-extra/clang-tidy/ExpandModularHeadersPPCallbacks.cpp
+++ clang-tools-extra/clang-tidy/ExpandModularHeadersPPCallbacks.cpp
@@ -30,12 +30,12 @@
       return;
 
     // FIXME: Why is this happening? We might be losing contents here.
-    if (!ContentCache.getRawBuffer())
+    llvm::Optional<StringRef> Data = ContentCache.getBufferDataIfLoaded();
+    if (!Data)
       return;
 
     InMemoryFs.addFile(File->getName(), /*ModificationTime=*/0,
-                       llvm::MemoryBuffer::getMemBufferCopy(
-                           ContentCache.getRawBuffer()->getBuffer()));
+                       llvm::MemoryBuffer::getMemBufferCopy(Data));
     // Remove the file from the set of necessary files.
     FilesToRecord.erase(File);
   }
Index: clang/include/clang/Basic/SourceManager.h
===================================================================
--- clang/include/clang/Basic/SourceManager.h
+++ clang/include/clang/Basic/SourceManager.h
@@ -194,9 +194,23 @@
     /// this content cache.  This is used for performance analysis.
     llvm::MemoryBuffer::BufferKind getMemoryBufferKind() const;
 
-    /// Get the underlying buffer, returning NULL if the buffer is not
-    /// yet available.
-    const llvm::MemoryBuffer *getRawBuffer() const { return Buffer.get(); }
+    /// Return the buffer, only if it has been loaded.
+    /// specified FileID, returning None if it's not yet loaded.
+    ///
+    /// \param FID The file ID whose contents will be returned.
+    llvm::Optional<llvm::MemoryBufferRef> getBufferIfLoaded() const {
+      if (Buffer)
+        return Buffer->getMemBufferRef();
+      return None;
+    }
+
+    /// Return a StringRef to the source buffer data, only if it has already
+    /// been loaded.
+    llvm::Optional<StringRef> getBufferDataIfLoaded() const {
+      if (Buffer)
+        return Buffer->getBuffer();
+      return None;
+    }
 
     /// Set the buffer.
     void setBuffer(std::unique_ptr<llvm::MemoryBuffer> B) {
@@ -207,10 +221,10 @@
     /// Set the buffer to one that's not owned (or to nullptr).
     ///
     /// \pre Buffer cannot already be set.
-    void setUnownedBuffer(const llvm::MemoryBuffer *B) {
+    void setUnownedBuffer(llvm::Optional<llvm::MemoryBufferRef> B) {
       assert(!Buffer && "Expected to be called right after construction");
       if (B)
-        setBuffer(llvm::MemoryBuffer::getMemBuffer(B->getMemBufferRef()));
+        setBuffer(llvm::MemoryBuffer::getMemBuffer(*B));
     }
 
     // If BufStr has an invalid BOM, returns the BOM name; otherwise, returns
Index: clang/lib/Basic/SourceManager.cpp
===================================================================
--- clang/lib/Basic/SourceManager.cpp
+++ clang/lib/Basic/SourceManager.cpp
@@ -153,7 +153,7 @@
 
   // Check that the file's size is the same as in the file entry (which may
   // have come from a stat cache).
-  if (getRawBuffer()->getBufferSize() != (size_t)ContentsEntry->getSize()) {
+  if (Buffer->getBufferSize() != (size_t)ContentsEntry->getSize()) {
     if (Diag.isDiagnosticInFlight())
       Diag.SetDelayedDiagnostic(diag::err_file_modified,
                                 ContentsEntry->getName());
@@ -361,7 +361,7 @@
     Clone->BufferOverridden = Cache->BufferOverridden;
     Clone->IsFileVolatile = Cache->IsFileVolatile;
     Clone->IsTransient = Cache->IsTransient;
-    Clone->setUnownedBuffer(Cache->getRawBuffer());
+    Clone->setUnownedBuffer(Cache->getBufferIfLoaded());
     return Clone;
   };
 
@@ -474,7 +474,8 @@
 SourceManager::getFakeContentCacheForRecovery() const {
   if (!FakeContentCacheForRecovery) {
     FakeContentCacheForRecovery = std::make_unique<SrcMgr::ContentCache>();
-    FakeContentCacheForRecovery->setUnownedBuffer(getFakeBufferForRecovery());
+    FakeContentCacheForRecovery->setUnownedBuffer(
+        getFakeBufferForRecovery()->getMemBufferRef());
   }
   return FakeContentCacheForRecovery.get();
 }
@@ -749,10 +750,7 @@
   if (!SLoc.isFile() || MyInvalid)
     return None;
 
-  if (const llvm::MemoryBuffer *Buf =
-          SLoc.getFile().getContentCache()->getRawBuffer())
-    return Buf->getBuffer();
-  return None;
+  return SLoc.getFile().getContentCache()->getBufferDataIfLoaded();
 }
 
 llvm::Optional<StringRef> SourceManager::getBufferDataOrNone(FileID FID) const {
Index: clang/lib/Serialization/ASTReader.cpp
===================================================================
--- clang/lib/Serialization/ASTReader.cpp
+++ clang/lib/Serialization/ASTReader.cpp
@@ -1542,7 +1542,7 @@
       = SourceMgr.getOrCreateContentCache(File, isSystem(FileCharacter));
     if (OverriddenBuffer && !ContentCache->BufferOverridden &&
         ContentCache->ContentsEntry == ContentCache->OrigEntry &&
-        !ContentCache->getRawBuffer()) {
+        !ContentCache->getBufferIfLoaded()) {
       auto Buffer = ReadBuffer(SLocEntryCursor, File->getName());
       if (!Buffer)
         return true;
Index: clang/lib/Serialization/ASTWriter.cpp
===================================================================
--- clang/lib/Serialization/ASTWriter.cpp
+++ clang/lib/Serialization/ASTWriter.cpp
@@ -1468,7 +1468,7 @@
     if (PP->getHeaderSearchInfo()
             .getHeaderSearchOpts()
             .ValidateASTInputFilesContent) {
-      auto *MemBuff = Cache->getRawBuffer();
+      auto MemBuff = Cache->getBufferIfLoaded();
       if (MemBuff)
         ContentHash = hash_value(MemBuff->getBuffer());
       else