Rebased PNaCl localmods in LLVM to 223109

lib/Support/MemoryBuffer.cpp

 //===--- MemoryBuffer.cpp - Memory Buffer implementation ------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 //  This file implements the MemoryBuffer interface.
@@ skipping 255 matching lines @@
   ErrorOr<std::unique_ptr<MemoryBuffer>> Ret =
       getOpenFileImpl(FD, Filename, FileSize, MapSize, Offset,
                       RequiresNullTerminator, IsVolatileSize);
   close(FD);
   return Ret;
 }
 
 static bool shouldUseMmap(int FD,
                           size_t FileSize,
                           size_t MapSize,
-                          off_t Offset,
+                          int64_t Offset,   // @LOCALMOD (?)
                           bool RequiresNullTerminator,
                           int PageSize,
                           bool IsVolatileSize) {
+
+  // @LOCALMOD-BEGIN
+  // Post 3.3-merge there seems to be a problem using mmap on cygwin. In the
+  // meantime, as a LOCALMOD, we disable usage of mmap in MemoryBuffer. The
+  // effect of this on the Windows/Cygwin toolchain can be a slightly slower
+  // developer-side linkage time.
+#if defined(__CYGWIN__)
+  return false;
+#endif
+  // @LOCALMOD-END
+
   // mmap may leave the buffer without null terminator if the file size changed
   // by the time the last page is mapped in, so avoid it if the file size is
   // likely to change.
   if (IsVolatileSize)
     return false;
 
   // We don't use mmap for small files because this can severely fragment our
   // address space.
   if (MapSize < 4 * 4096 || MapSize < (unsigned)PageSize)
     return false;
@@ skipping 137 matching lines @@
   sys::ChangeStdinToBinary();
 
   return getMemoryBufferForStream(0, "<stdin>");
 }
 
 MemoryBufferRef MemoryBuffer::getMemBufferRef() const {
   StringRef Data = getBuffer();
   StringRef Identifier = getBufferIdentifier();
   return MemoryBufferRef(Data, Identifier);
 }