Index: clang/include/clang/Basic/SourceManager.h
===================================================================
--- clang/include/clang/Basic/SourceManager.h
+++ clang/include/clang/Basic/SourceManager.h
@@ -145,7 +145,7 @@
     ///
     /// This is lazily computed.  The lines are owned by the SourceManager
     /// BumpPointerAllocator object.
-    LineOffsetMapping SourceLineCache;
+    mutable LineOffsetMapping SourceLineCache;
 
     /// Indicates whether the buffer itself was provided to override
     /// the actual file contents.
@@ -718,7 +718,7 @@
   /// These ivars serve as a cache used in the getLineNumber
   /// method which is used to speedup getLineNumber calls to nearby locations.
   mutable FileID LastLineNoFileIDQuery;
-  mutable SrcMgr::ContentCache *LastLineNoContentCache;
+  mutable const SrcMgr::ContentCache *LastLineNoContentCache;
   mutable unsigned LastLineNoFilePos;
   mutable unsigned LastLineNoResult;
 
Index: clang/lib/Basic/SourceManager.cpp
===================================================================
--- clang/lib/Basic/SourceManager.cpp
+++ clang/lib/Basic/SourceManager.cpp
@@ -1259,20 +1259,20 @@
 #endif
 
 static LLVM_ATTRIBUTE_NOINLINE void
-ComputeLineNumbers(DiagnosticsEngine &Diag, ContentCache *FI,
+ComputeLineNumbers(DiagnosticsEngine &Diag, const ContentCache &FI,
                    llvm::BumpPtrAllocator &Alloc,
                    const SourceManager &SM, bool &Invalid);
-static void ComputeLineNumbers(DiagnosticsEngine &Diag, ContentCache *FI,
+static void ComputeLineNumbers(DiagnosticsEngine &Diag, const ContentCache &FI,
                                llvm::BumpPtrAllocator &Alloc,
                                const SourceManager &SM, bool &Invalid) {
   // Note that calling 'getBuffer()' may lazily page in the file.
   llvm::Optional<llvm::MemoryBufferRef> Buffer =
-      FI->getBufferOrNone(Diag, SM.getFileManager(), SourceLocation());
+      FI.getBufferOrNone(Diag, SM.getFileManager(), SourceLocation());
   Invalid = !Buffer;
   if (Invalid)
     return;
 
-  FI->SourceLineCache = LineOffsetMapping::get(*Buffer, Alloc);
+  FI.SourceLineCache = LineOffsetMapping::get(*Buffer, Alloc);
 }
 
 LineOffsetMapping LineOffsetMapping::get(llvm::MemoryBufferRef Buffer,
@@ -1322,7 +1322,7 @@
     return 1;
   }
 
-  ContentCache *Content;
+  const ContentCache *Content;
   if (LastLineNoFileIDQuery == FID)
     Content = LastLineNoContentCache;
   else {
@@ -1334,14 +1334,14 @@
       return 1;
     }
 
-    Content = const_cast<ContentCache*>(Entry.getFile().getContentCache());
+    Content = Entry.getFile().getContentCache();
   }
 
   // If this is the first use of line information for this buffer, compute the
   /// SourceLineCache for it on demand.
   if (!Content->SourceLineCache) {
     bool MyInvalid = false;
-    ComputeLineNumbers(Diag, Content, ContentCacheAlloc, *this, MyInvalid);
+    ComputeLineNumbers(Diag, *Content, ContentCacheAlloc, *this, MyInvalid);
     if (Invalid)
       *Invalid = MyInvalid;
     if (MyInvalid)
@@ -1685,8 +1685,7 @@
   if (Line == 1 && Col == 1)
     return FileLoc;
 
-  ContentCache *Content
-    = const_cast<ContentCache *>(Entry.getFile().getContentCache());
+  const ContentCache *Content = Entry.getFile().getContentCache();
   if (!Content)
     return SourceLocation();
 
@@ -1694,7 +1693,7 @@
   // SourceLineCache for it on demand.
   if (!Content->SourceLineCache) {
     bool MyInvalid = false;
-    ComputeLineNumbers(Diag, Content, ContentCacheAlloc, *this, MyInvalid);
+    ComputeLineNumbers(Diag, *Content, ContentCacheAlloc, *this, MyInvalid);
     if (MyInvalid)
       return SourceLocation();
   }
Index: clang/lib/Lex/ScratchBuffer.cpp
===================================================================
--- clang/lib/Lex/ScratchBuffer.cpp
+++ clang/lib/Lex/ScratchBuffer.cpp
@@ -37,10 +37,10 @@
   else {
     // Clear out the source line cache if it's already been computed.
     // FIXME: Allow this to be incrementally extended.
-    auto *ContentCache = const_cast<SrcMgr::ContentCache *>(
-        SourceMgr.getSLocEntry(SourceMgr.getFileID(BufferStartLoc))
-                 .getFile().getContentCache());
-    ContentCache->SourceLineCache = SrcMgr::LineOffsetMapping();
+    SourceMgr.getSLocEntry(SourceMgr.getFileID(BufferStartLoc))
+        .getFile()
+        .getContentCache()
+        ->SourceLineCache = SrcMgr::LineOffsetMapping();
   }
 
   // Prefix the token with a \n, so that it looks like it is the first thing on