Add (unsupported experimental) feature allowing byte aligned bitcode.

lib/Bitcode/NaCl/Analysis/NaClBitcodeAnalyzer.cpp

 //===-- NaClBitcodeAnalyzer.cpp - Bitcode Analyzer ------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #define DEBUG_TYPE "nacl-bitcode-analyzer"
@@ skipping 390 matching lines @@
 int AnalyzeBitcodeInBuffer(const std::unique_ptr<MemoryBuffer> &Buf,
                            raw_ostream &OS,
                            const AnalysisDumpOptions &DumpOptions) {
   DEBUG(dbgs() << "-> AnalyzeBitcodeInBuffer\n");
 
   if (Buf->getBufferSize() & 3)
     return Error("Bitcode stream should be a multiple of 4 bytes in length");
 
   const unsigned char *BufPtr = (const unsigned char *)Buf->getBufferStart();
   const unsigned char *EndBufPtr = BufPtr + Buf->getBufferSize();
+  const unsigned char *HeaderPtr = BufPtr;

[jvoung (off chromium), 2015/05/08 17:55:01]

I know Header.Read(x, ...) actually modifies x, but I'm not sure why this is
changed now? Is the NaClBistreamReader tolerant of starting where the header
begins instead of after?

[Karl, 2015/05/08 21:09:00]

I changed this a while back. The problem is that the bitstream reader assumes
the beginning passed in is the beginning of the corresponding file it comes
from. Hence, if you pass in the modified BufPtr (as passed to Header.Read(), it
will incorrectly report bitcode byte locations.

The InitialAddress value let adjust the beginning to the position past the
header. However, the old code wasn't doing that, because of the fact that BufPtr
started past the beginning of the bitcode header.

I fixed some of the applications, but I apparently missed a few (including this
one).

I agree that it would be nice to fix Header.Read() to not update the pointer,
and added it to this CL.

The new constructors for NaClBitstreamReader with a Header argument
automatically set the initial index based on the size of the header, allowing
one not to pass that value in.

[jvoung (off chromium), 2015/05/11 17:51:39]

Thanks, that's easier to follow.

 
   NaClBitcodeHeader Header;
-  if (Header.Read(BufPtr, EndBufPtr))
+  if (Header.Read(HeaderPtr, EndBufPtr))
     return Error("Invalid PNaCl bitcode header");
 
   if (!Header.IsSupported())
     errs() << "Warning: " << Header.Unsupported() << "\n";
 
   if (!Header.IsReadable())
     Error("Bitcode file is not readable");
 
-  NaClBitstreamReader StreamFile(BufPtr, EndBufPtr);
+  NaClBitstreamReader StreamFile(
+      getNonStreamedMemoryObject(BufPtr, EndBufPtr), Header);
   NaClBitstreamCursor Stream(StreamFile);
 
   unsigned NumTopBlocks = 0;
 
   // Print out header information.
   for (size_t i = 0, limit = Header.NumberFields(); i < limit; ++i) {
     OS << Header.GetField(i)->Contents() << "\n";
   }
   if (Header.NumberFields()) OS << "\n";
 
@@ skipping 27 matching lines @@
   ErrorOr<std::unique_ptr<MemoryBuffer>> ErrOrFile =
       MemoryBuffer::getFileOrSTDIN(InputFilename);
   if (std::error_code EC = ErrOrFile.getError())
     return Error(Twine("Error reading '") + InputFilename + "': " +
                  EC.message());
 
   return AnalyzeBitcodeInBuffer(ErrOrFile.get(), OS, DumpOptions);
 }
 
 } // namespace llvm