Remove llvm::MemoryBuffer const_casts

Summary:
llvm has grown a WritableMemoryBuffer class, which is convertible
(inherits from) a MemoryBuffer. We can use it to avoid conts_casting the
buffer contents when we want to write to it.

Reviewers: dblaikie, rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D41387

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@321167 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Basic/SourceManager.cpp

@@ -125,11 +125,12 @@ llvm::MemoryBuffer *ContentCache::getBuffer(DiagnosticsEngine &Diag,
   // possible.
   if (!BufferOrError) {
     StringRef FillStr("<<<MISSING SOURCE FILE>>>\n");
-    Buffer.setPointer(MemoryBuffer::getNewUninitMemBuffer(
-                          ContentsEntry->getSize(), "<invalid>").release());
-    char *Ptr = const_cast<char*>(Buffer.getPointer()->getBufferStart());
+    auto BackupBuffer = llvm::WritableMemoryBuffer::getNewUninitMemBuffer(
+        ContentsEntry->getSize(), "<invalid>");
+    char *Ptr = BackupBuffer->getBufferStart();
     for (unsigned i = 0, e = ContentsEntry->getSize(); i != e; ++i)
       Ptr[i] = FillStr[i % FillStr.size()];
+    Buffer.setPointer(BackupBuffer.release());
 
     if (Diag.isDiagnosticInFlight())
       Diag.SetDelayedDiagnostic(diag::err_cannot_open_file,

lib/Lex/Preprocessor.cpp

@@ -420,10 +420,9 @@ bool Preprocessor::SetCodeCompletionPoint(const FileEntry *File,
   CodeCompletionFile = File;
   CodeCompletionOffset = Position - Buffer->getBufferStart();
 
-  std::unique_ptr<MemoryBuffer> NewBuffer =
-      MemoryBuffer::getNewUninitMemBuffer(Buffer->getBufferSize() + 1,
-                                          Buffer->getBufferIdentifier());
-  char *NewBuf = const_cast<char*>(NewBuffer->getBufferStart());
+  auto NewBuffer = llvm::WritableMemoryBuffer::getNewUninitMemBuffer(
+      Buffer->getBufferSize() + 1, Buffer->getBufferIdentifier());
+  char *NewBuf = NewBuffer->getBufferStart();
   char *NewPos = std::copy(Buffer->getBufferStart(), Position, NewBuf);
   *NewPos = '\0';
   std::copy(Position, Buffer->getBufferEnd(), NewPos+1);