Add a bitcode parser constructor for parallel parsing.

include/llvm/Bitcode/NaCl/NaClBitcodeParser.h

 //===- NaClBitcodeParser.h -----------------------------------*- C++ -*-===//
 //     Low-level bitcode driver to parse PNaCl bitcode files.
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
@@ skipping 579 matching lines @@
 
   // The current record (within the block) being processed.
   NaClBitcodeRecord Record;
 
   // The listener (if any) to use.
   NaClBitcodeParserListener *Listener;
 
   // The error stream to use if non-null (uses errs() if null).
   raw_ostream *ErrStream;
 
-  // Creates a block parser to parse the block associated with the
-  // bitcode entry that defines the beginning of a block. This
-  // instance actually parses the corresponding block.
+  // Creates a block parser to parse the block associated with the bitcode entry
+  // that defines the beginning of a block. This instance actually parses the
+  // corresponding block. Inherits the bitstream cursor from the
+  // EnclosingParser.
   NaClBitcodeParser(unsigned BlockID, NaClBitcodeParser *EnclosingParser)
       : EnclosingParser(EnclosingParser),
         Block(BlockID, EnclosingParser->Record),
         Record(Block),
         Listener(EnclosingParser->Listener),
         ErrStream(EnclosingParser->ErrStream)
   {}
 
+  // Same as above, but use the supplied bitstream cursor (instead of
+  // inheriting from the enclosing parser). This constructor allows
+  // parallel parsing of subblocks, by allowing the caller to generate
+  // a different Cursor for each block to be parsed in parallel.
+  NaClBitcodeParser(unsigned BlockID, NaClBitcodeParser *EnclosingParser,
+                    NaClBitstreamCursor &Cursor)
+      : EnclosingParser(EnclosingParser),
+        Block(BlockID, Cursor),
+        Record(Block),
+        Listener(EnclosingParser->Listener),
+        ErrStream(EnclosingParser->ErrStream)
+  {}
+
   /// Defines the listener for this block, and all enclosing blocks,
   /// to be the given listener. Should be set in the constructor.
   void SetListener(NaClBitcodeParserListener* UseListener) {
     Listener = UseListener;
   }
 
 private:
   // Special constant identifying the top-level instance.
   static const unsigned ILLEGAL_BLOCK_ID = UINT_MAX;
 
@@ skipping 19 matching lines @@
   bool ParseBlockInternal();
 
   void operator=(const NaClBitcodeParser &Parser) = delete;
   NaClBitcodeParser(const NaClBitcodeParser &Parser) = delete;
 
 };
 
 }  // namespace llvm
 
 #endif