Refactor bitcode reader to simplify control.

[kschimpf]

Summary

Modifies the bitcode reader such that the same logic is used for
both memory buffers and data streams. The incremental parsing
was factored into startParse, continueParse, and finishParse.
All parses (incremental or non-incremental) begin with startParse.
Then zero (or more) calls to continueParse incrementally read more
input, picking up from where the last call left off. finishParse
materializes any additional parts, based on the flags passed to startParse.

[jvoung]

lib/Bitcode/Reader/BitcodeReader.cpp

234

be consistent about capitalization in comments

one line starts with "parsed input" and another line starts with "Parsed input" =)

250–251

Don't need explicit anymore, though that transition was a while back so not really related to this CL.

277

Variable name is different from comment "MaterializeAll" vs "ShouldMaterializeAll" -- make them the same? I see that in the actual definition you're trying to avoid conflicting with the field name...

[kschimpf]

• Merge branch 'master' of http://llvm.org/git/llvm into readfac1
• Working version. Save state.
• Cleanup startParse.
• Cleaned up code.
• Fix nit.
• Merge branch 'master' of http://llvm.org/git/llvm into readfac1

[kschimpf]

DId all changes except adding test that forward block address references get resolved on lazy loads.

lib/Bitcode/Reader/BitcodeReader.cpp

234

Done.

250–251

Done.

268–269

Sorry, my fault. I followed the syntax of ConstantPlaceHolder below. Changing to follow coding standards.

268–269

Done.

276

Good point. Fixing.

277

Fixing the names to be consistent. Fixing name conflict by prefixing assignments of field names with "this->".

386

Done.

390

Done.

398

I guess the first part of the problem is that there are 2 notions of parse state:

1. The field ParseState that names the state of the parser, and
2. NextUnreadBit which defines where to continue the parse on return (in case a function body gets parsed between calls).

I also overloaded the return value with this update. Refactoring to do less and be more clear.

413

The refactoring is a bit better now. Hopefully good enough.

2845

Done.

3277

After talking to Derek, I realized what was the issue I was missing. I'l summarize what I understand:

1. When streaming, we want to "return" as soon as possible, without having to force all bitcode to be scanned. This reduces the cost of (potential) blocking calls to the data streamer.

2. Control can return to the caller without having completed the parse. However, the parsed portions must be consistent (i.e. forward block address references have been resolved).

Based on this, I've modified the code to lift the materializeForwardReferencedFunctions into startParse.

3281

I agree that there should be some type of forward reference unit test to verify we can lazy evaluate these forward-referenced block addresses.

I also agree that for the use by llvm-dis, my original code worked because it eventually calls materializeAllPermanently. I think I may have been confused about the full expectation of "streamed" (or lazy) was because of this.

4616

Done.

[• rafael]

include/llvm/Support/StreamingMemoryObject.h

75 ↗

(On Diff #23431)

Why do you need this? The streamer will return how many bytes were read and can handle a larger request.

Also, why does it need to be part of this patch? It looks like this patch has many independent changes in it.

88 ↗

(On Diff #23431)

Why the extra logic? If objectsize is known it is the same as BytesRead, no?

[kschimpf]

include/llvm/Support/StreamingMemoryObject.h

75 ↗

(On Diff #23431)

This was added to handle the case of when one is parsing a wrapped bitcode file. In such cases, you do not need to do another read (which may block until it succeeds). That was the intent of this change. However, a simpler approach would be to allow the extra read, and then not set ObjectSize (below) if already set.

I will remove this change, and add the conditional assignment to ObjectSize below.

I changed it in this CL because it didn't cause a problem until I fixed that materializing a module (when streaming) didn't actually read all of the bitcode file. When that change was added, tests failed and this issue was exposed.

I will remove the changes StreamingMemoryObject.{h,cpp} and put in a separate CL.

88 ↗

(On Diff #23431)

No, they aren't necessarily the same.

The problem happens when you have a wrapped bitcode file, and was not exposed until I fixed the case that we weren't reading the entire bitcode when materializing lazily. Then, a bunch of test cases failed.

When I looked into it, this is what I discovered:

1. The wrapped bitcode was smaller than kChunkSize. Hence, the initial read set BytesRead to the size of the wrapped file on first read.

2. The wrapper was then read, and set ObjectSize, which corresponded to 4 bytes smaller than BytesRead.

This is the reason I changed this file as I did.

[jvoung]

lib/Bitcode/Reader/BitcodeReader.cpp

242

nit: This is usually 0 or 1, but it seems unexpected for this field to be named "NumModulesParsed", and yet have the type be "bool". Rename or change type?

413

Thanks -- this is better.

For a while I was also wondering how many places need to be aware of setting the state to ParseError, but I think it's just continueParse() because most/all searching for bit position, etc. goes through that.

3159

Does this need to be cleanupOnError(EC) also?

3197

This covers two states? InsideModule and AtTopLevel? It might be more clear if you list them out so it's clear what the "break" corresponds to (AtTopLevel).

Previously, the Stream.JumpToBit(NextUnreadBit); was only needed when InsideModule... is it now needed for AtTopLevel too?

3292

"NoMorInput" -> "NoMoreInput"

It could also be that more states >= NoMoreInput are added as code evolves, but not handled here. Can the compiler accept/handle a "static_assert(ParseState < NoMoreInput, "...") to catch what happens if more states are added after NoMoreInput but not handled by this switch?

4664

Is this necessary at this point? Should that already be covered by the " // Iterate over the module, deserializing any functions that are still on disk" loop?

4664–4665

The "promise" comment from "above" is removed now, so you could update this comment.

[kschimpf]

Fix issues raised by jvoung, and remove changes now in D8907.

[kschimpf]

lib/Bitcode/Reader/BitcodeReader.cpp

242

Good catch. I did meant to use size_t. Fixing.

413

That is correct and was the intent. State updates (and bit positioning) is intentionally now localized to continueParse.

The only exception is in ParseModule, which updates the state to state whether it returned without completing.

3159

Yes. Good catch. Fixing.

3197

The jumpToBit is needed because various "materialize" methods may be called between calls to continueParse. By forcing a jumpToBit to happen at all calls to continueParse, we no longer need to know where the materialize methods leave the bitcursor.

While I did not see an example of an error caused by interleaved calls to materialize, I was very suspicious that they could occur, and wanted to make sure that this would not happen. Hence, I made sure that continueParse always resets the position to where it left off.

I will fix to not use default, so that a corresponding warning will be generated if a new value is added to the enumeration.

3292

Fixed string. Also removed "default" case and made all states explicit. This will force a warning if a new state is added.

4651

Removing the comment about being after a function body. This is no longer true. A call to materializeMetadata would put us some place else in the bitcode file.

4664

In correct bitcode files, you are right. However, if the function doesn't define any function blocks, but (incorrectly) references function block addresses, this code will cause the error to be generated.

However, looking at the following instruction, this is checked anyway. Removing.

4664–4665

Done.

[kschimpf]

Fix issues in diff 23431.

[kschimpf]

• Merge branch 'master' into readfac1
• Fix issues raised by merge.
• Merge branch 'master' of http://llvm.org/git/llvm into readfac1
• Fix tests to use old-style parser.

[kschimpf]

• Fix nits.

[kschimpf]

Now that the issues with the streaming memory object has been fixed, I have updated this CL for review.

Note that I added a CL flag "-old-lazy-bitcode-parser". This was done to deal with a bug fixed by this CL. That is, in the old code, when you materialized a module, it didn't check if there was any additional data in the bitcode file. The new code fixes this by calling "finishParse". However, there are a couple of (bitcode binary) tests that were generated with this violation. Hence, the flag was added to fix this problem.

I'm willing to remove this flag in either (1) a later review, or (2) in a later revision. However, for this review I made the issues explicit so that the problem can be seen.

[filcab]

In D8786#179791, @kschimpf wrote:

However, there are a couple of (bitcode binary) tests that were generated with this violation. Hence, the flag was added to fix this problem.

I'm willing to remove this flag in either (1) a later review, or (2) in a later revision. However, for this review I made the issues explicit so that the problem can be seen.

Let me know which ones have bugs. They might be easy-ish to reconstruct (especially since I have some additional practice in fiddling with bc files, now (Can't promise to deal with them very quickly, though).

lib/Bitcode/Reader/BitcodeReader.cpp

282–283

Why the empty line?

294

http://llvm.org/docs/CodingStandards.html#doxygen-use-in-documentation-comments
^^ This changed recently.

Omit \brief if the brief description is just a sentence. (You might want to add the '.' at the end, though)

771

Omit \brief.

785

Omit \brief.

3227

We're already at top level, no? (line 3234)
I might be missing something, but it looks like we're at top level, and saw an EndBlock. Shouldn't this be an error?

[kschimpf]

• Merge branch 'master' of http://llvm.org/git/llvm into readfac1
• Fix issues raised by filcab.

[kschimpf]

Fixes based on feedback by Filipe.

lib/Bitcode/Reader/BitcodeReader.cpp

282–283

Removed.

771

Done.

785

Done.

3227

I agree that we should be at top level.

I also agree that it appears weird that we allow extra (unmathced) EndBlocks. This has been allowed by the bitcode reader/writer for years. I just wasn't willing to make the leap that I should remove this.

However, I tried removing it (and making it an error), and no tests failed. Hence, Converting this to an error.

4656

Moved the iterating of functions to before the call to finishParse. This deals with the problems I was having with tests in test/Bitcode/invalid.test (i.e. Inputs/invalid-fwdref-type-mismatch-2.bc and Inputs/invalid-load-ptr-type.bc). These two files had multiple errors (the one they intended which was inside a function body, and the one probably not intended - extraneous stuff at the end of the bitcode file).

This removes the need for the command line flag UseOldLazyBitcodeParse, and I have deleted it.

[filcab]

Hi Karl,

The files came straight from the fuzzer, so it is likely have more than one error. If, in order to support them (where support is: keep the test working and diagnosing what we want), you have to change the code in a convoluted way, I would prefer to change the test.

If the change is minimal and not a problem (doesn't impact legibility or architecture), then keeping the tests as they are is not a problem either. I just want to avoid having worse code just so we don't have to re-do some tests.

Of course, if we started crashing on the tests, that's a problem :-)

Thanks,

Filipe

(Phab butchered the comment in my email. Editing it to get a complete history in Phabricator)

[kschimpf]

• Fix invalid bitcode tests with more than one error.
• Merge branch 'master' into readfac1

[kschimpf]

In addition to moving the code back in materializeModule, I fixed three tests. Two of them were fuzz tests where I "truncated" the file to the end of the module block. The other test did not have anything after a bad abbreviation definition, and the code file was incomplete. So I generated a replacement test that was well structured otherwise (i.e. only had that one error in it).

include/llvm/Bitcode/BitstreamReader.h

328

This code fixes the state of the bit streamer when no more input is found. As a result, method AtEndOfStream now works correctly.

lib/Bitcode/Reader/BitcodeReader.cpp

3226

Discovered that the Bitstream::EndBLock was "hiding" a bug int the bitstream reader when processing a data stream. That is, when using a data stream, the size is not set until after the eof is reached. Hence, when Stream.AtEndOfStream() was called above, it would return false even when at the eof. The actual problem was in FillCurWord, which did not set the bit position correctly when there was no more input.

The old code worked because the read (at eof) would return zero, and is understood as an end block. By returning success for this value, it would hide this problem.

I also improved the error message so that once can see where the reader thought the eof should be, if there is miscellaneous stuff at the end of the bit code file. This makes it easier to know where to cut a test file in such cases.

4657

Now that the eof checking is fixed, I moved this back where it was in an earlier version of this CL.

[filcab]

Hi Karl,

Really sorry for the delay.
LGTM on my part, as long as you add the test for the error message and do the fix.

Thank you,

Filipe

lib/Bitcode/Reader/BitcodeReader.cpp

772

Nit: Put more words on the first line.

776

Nit: If it's for docs, it's probably best to start with an uppercase letter.

3229

Thank you!

3233

errs()? Or StrBuf?
Please also add a test for this error message.

[kschimpf]

• Merge branch 'master' of http://llvm.org/git/llvm into readfac1
• Fixes associated with review by Filipe.

[kschimpf]

Fixed issues raised by Filipe.

lib/Bitcode/Reader/BitcodeReader.cpp

772

Done.

776

Done.

3233

Good catch. I meant StrBuf, so that we can use the same API for all errors.

[• rafael]

Applying the patch locally to take a better look.

lib/Bitcode/Reader/BitcodeReader.cpp

269–281

Please commit the pure cleanup bits first:

using \ instead of @
starting functions with lowercase names.

3234

This looks a bit much to be honest. Corrupted files are not that common and it is trivial to set a breakpoint to find the state.

3245

This is always 0 or 1. Use a boolean instead.

[• rafael]

I got the following test failures locally:

LLVM :: Bitcode/invalid.test
LLVM :: tools/gold/invalid.ll

[kschimpf]

This CL has gotten a bit long, and hard to read (to many versions). Moved to a new CL http://reviews.llvm.org/D10518

lib/Bitcode/Reader/BitcodeReader.cpp

269–281

I assume this has already been done. The new CL doesn't have suc cases anymore.

3234

Simplified in new CL to do same as before.

3245

This was already fixed in master.

[kschimpf]

This CL has gotten a bit long, and hard to read (to many versions). Moved to a new CL http://reviews.llvm.org/D10518

include/llvm/Bitcode/BitstreamReader.h

void fillCurWord() {
     // Read the next word from the stream.
     uint8_t Array[sizeof(word_t)] = {0};
 
     uint64_t BytesRead =
         BitStream->getBitcodeBytes().readBytes(Array, sizeof(Array), NextChar);
 
     // If we run out of data, stop at the end of the stream.
     if (BytesRead == 0) {
       Size = NextChar;
+      CurWord = 0;
+      BitsInCurWord = 0;
       return;
     }
 
     CurWord =
         support::endian::read<word_t, support::little, support::unaligned>(
             Array);
     NextChar += BytesRead;
     BitsInCurWord = BytesRead * 8;

lib/Bitcode/Reader/BitcodeReader.cpp

 #include "llvm/IR/OperandTraits.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Support/DataStream.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/Format.h"
 #include <deque>
 using namespace llvm;
 
 namespace {
 enum {
   SWITCH_INST_MAGIC = 0x4B5 // May 2012 => 1205 => Hex
 };
 
public:
   void AssignValue(Metadata *MD, unsigned Idx);
   void tryToResolveCycles();
 };
 
 class BitcodeReader : public GVMaterializer {
   LLVMContext &Context;
   DiagnosticHandlerFunction DiagnosticHandler;
   Module *TheModule;
+  // The following two fields define the type of memory to parse.
   std::unique_ptr<MemoryBuffer> Buffer;
+  DataStreamer *Streamer;
   std::unique_ptr<BitstreamReader> StreamFile;
   BitstreamCursor Stream;
-  DataStreamer *LazyStreamer;
-  uint64_t NextUnreadBit;
   bool SeenValueSymbolTable;
 
   std::vector<Type*> TypeList;
   BitcodeReaderValueList ValueList;
   BitcodeReaderMDValueList MDValueList;
   std::vector<Comdat *> ComdatList;
   SmallVector<Instruction *, 64> InstructionList;
 
class BitcodeReader : public GVMaterializer {
   /// for a more compact encoding.  Some instruction operands are not
   /// relative to the instruction ID: basic block numbers, and types.
   /// Once the old style function blocks have been phased out, we would
   /// not need this flag.
   bool UseRelativeIDs;
 
   /// True if all functions will be materialized, negating the need to process
   /// (e.g.) blockaddress forward references.
-  bool WillMaterializeAllForwardRefs;
+  bool WillMaterializeAllForwardRefs = false;
 
   /// Functions that have block addresses taken.  This is usually empty.
   SmallPtrSet<const Function *, 4> BlockAddressesTaken;
 
   /// True if any Metadata block has been materialized.
-  bool IsMetadataMaterialized;
+  bool IsMetadataMaterialized = false;
+
+  /// True if meta data should initially be skipped.
+  bool ShouldLazyLoadMetadata = false;
+
+  /// The name of state of the parse. Along with NextUnreadBit, they
+  /// define the state of the parse between calls to continueParse().
+  enum BitcodeReaderState {
+    AtStart,
+    AtTopLevel,    // Processing top-level records.
+    InsideModule,  // Processing records inside a module block.
+    // All states below here represent cases where input shouldn't be parsed.
+    NoMoreInput,   // Generic marker for having parsed input.
+    ReachedEof,     // Parsed input, but not necessary materializations.
+    FinishedParse, // Parsed input and materialized necessary parts.
+    ParseError,    // An error has occurred, stop parsing.
+  } ParseState = AtStart;
+
+  /// The position (within the bitcode) where continueParse() left off, and used
+  /// to set input position on the next call to continueParse().
+  uint64_t NextUnreadBit = 0;
+
+  /// The number of modules read at the top level.
+  size_t NumModulesParsed = 0;
 
   bool StripDebugInfo = false;
 
 public:
   std::error_code Error(BitcodeError E, const Twine &Message);
   std::error_code Error(BitcodeError E);
   std::error_code Error(const Twine &Message);
 
-  explicit BitcodeReader(MemoryBuffer *buffer, LLVMContext &C,
-                         DiagnosticHandlerFunction DiagnosticHandler);
-  explicit BitcodeReader(DataStreamer *streamer, LLVMContext &C,
-                         DiagnosticHandlerFunction DiagnosticHandler);
+  BitcodeReader(MemoryBuffer *Buffer, LLVMContext &C,
+  BitcodeReader(DataStreamer *Streamer, LLVMContext &C,
   ~BitcodeReader() override { FreeState(); }
 
   std::error_code materializeForwardReferencedFunctions();
 
   void FreeState();
 
   void releaseBuffer();
 
   bool isDematerializable(const GlobalValue *GV) const override;
   std::error_code materialize(GlobalValue *GV) override;
   std::error_code materializeModule(Module *M) override;
   std::vector<StructType *> getIdentifiedStructTypes() const override;
   void dematerialize(GlobalValue *GV) override;
 
-  /// @brief Main interface to parsing a bitcode buffer.
-  /// @returns true if an error occurred.
-  std::error_code ParseBitcodeInto(Module *M,
-                                   bool ShouldLazyLoadMetadata = false);
+  /// \brief Starts parse of bitcode. Materializes during parse based on flags.
+  ///
+  /// \param M the module to build.
+  /// \param ShouldMaterializeAll true when the module should be materialized
+  /// completely before returning. Otherwise, function bodies are only loaded on
+  /// demand.
+  /// \param ShouldLazyLoadMetadata true when the metadata blocks should be
+  /// parsed.
+  ///
+  /// \returns true if an error occurred.
+  std::error_code parseBitcodeInto(Module *M,
+                                   bool ShouldMaterializeAll,
+                                   bool ShouldLazyLoadMetadata);
 
-  /// @brief Cheap mechanism to just extract module triple
-  /// @returns true if an error occurred.
+  /// Cheap mechanism to just extract module triple.
+  /// \returns true if an error occurred.
   ErrorOr<std::string> parseTriple();
 
   static uint64_t decodeSignRotatedValue(uint64_t V);
 
   /// Materialize any deferred Metadata block.
   std::error_code materializeMetadata() override;
 
   void setStripDebugInfo() override;
 
 private:
   std::vector<StructType *> IdentifiedStructTypes;
   StructType *createIdentifiedStructType(LLVMContext &Context, StringRef Name);
   StructType *createIdentifiedStructType(LLVMContext &Context);
 
   Type *getTypeByID(unsigned ID);
   Value *getFnValueByID(unsigned ID, Type *Ty) {
     if (Ty && Ty->isMetadataTy())
       return MetadataAsValue::get(Ty->getContext(), getFnMetadataByID(ID));
Value *getValueSigned(SmallVectorImpl<uint64_t> &Record, unsigned Slot,
     if (Slot == Record.size()) return nullptr;
     unsigned ValNo = (unsigned)decodeSignRotatedValue(Record[Slot]);
     // Adjust the ValNo, if it was encoded relative to the InstNum.
     if (UseRelativeIDs)
       ValNo = InstNum - ValNo;
     return getFnValueByID(ValNo, Ty);
   }
 
+  /// \name Functions that parses bitcode files, other than skipped blocks based
+  /// on flags to parseBitcodeInto().
+  /// @{
+  std::error_code startParse();
+  std::error_code continueParse();
+  std::error_code finishParse();
+  /// @}
+
+  // Changes the parse state to the new value.
+  void setParseState(BitcodeReaderState NewValue) {
+    NextUnreadBit = Stream.GetCurrentBitNo();
+    ParseState = NewValue;
+  }
+
+  // Changes the parse state to ParseError if given an error.
+  void setParseStateIfError(std::error_code EC) {
+    NextUnreadBit = Stream.GetCurrentBitNo();
+    if (EC)
+      ParseState = ParseError;
+  }
+
   /// Converts alignment exponent (i.e. power of two (or zero)) to the
   /// corresponding alignment to use. If alignment is too large, returns
   /// a corresponding error code.
   std::error_code parseAlignmentValue(uint64_t Exponent, unsigned &Alignment);
   std::error_code ParseAttrKind(uint64_t Code, Attribute::AttrKind *Kind);
-  std::error_code ParseModule(bool Resume, bool ShouldLazyLoadMetadata = false);
+  std::error_code ParseModule();
   std::error_code ParseAttributeBlock();
   std::error_code ParseAttributeGroupBlock();
   std::error_code ParseTypeTable();
   std::error_code ParseTypeTableBody();
 
   std::error_code ParseValueSymbolTable();
   std::error_code ParseConstants();
   std::error_code RememberAndSkipFunctionBody();
   /// Save the positions of the Metadata blocks and skip parsing the blocks.
   std::error_code rememberAndSkipMetadata();
   std::error_code ParseFunctionBody(Function *F);

 
 static std::error_code Error(DiagnosticHandlerFunction DiagnosticHandler,
                              const Twine &Message) {
   return Error(DiagnosticHandler,
                make_error_code(BitcodeError::CorruptedBitcode), Message);
 }
 
 std::error_code BitcodeReader::Error(BitcodeError E, const Twine &Message) {
+  setParseState(ParseError);
   return ::Error(DiagnosticHandler, make_error_code(E), Message);
 }
 
 std::error_code BitcodeReader::Error(const Twine &Message) {
+  setParseState(ParseError);
   return ::Error(DiagnosticHandler,
                  make_error_code(BitcodeError::CorruptedBitcode), Message);
 }
 
 std::error_code BitcodeReader::Error(BitcodeError E) {
+  setParseState(ParseError);
   return ::Error(DiagnosticHandler, make_error_code(E));
 }
 
 static DiagnosticHandlerFunction getDiagHandler(DiagnosticHandlerFunction F,
                                                 LLVMContext &C) {
   if (F)
     return F;
   return [&C](const DiagnosticInfo &DI) { C.diagnose(DI); };
 }
 
-BitcodeReader::BitcodeReader(MemoryBuffer *buffer, LLVMContext &C,
+BitcodeReader::BitcodeReader(MemoryBuffer *Buffer, LLVMContext &C,
                              DiagnosticHandlerFunction DiagnosticHandler)
     : Context(C), DiagnosticHandler(getDiagHandler(DiagnosticHandler, C)),
-      TheModule(nullptr), Buffer(buffer), LazyStreamer(nullptr),
-      NextUnreadBit(0), SeenValueSymbolTable(false), ValueList(C),
-      MDValueList(C), SeenFirstFunctionBody(false), UseRelativeIDs(false),
-      WillMaterializeAllForwardRefs(false), IsMetadataMaterialized(false) {}
+      TheModule(nullptr), Buffer(Buffer), Streamer(nullptr),
+      SeenValueSymbolTable(false), ValueList(C),
+      MDValueList(C), SeenFirstFunctionBody(false), UseRelativeIDs(false) {}
 
-BitcodeReader::BitcodeReader(DataStreamer *streamer, LLVMContext &C,
+BitcodeReader::BitcodeReader(DataStreamer *Streamer, LLVMContext &C,
                              DiagnosticHandlerFunction DiagnosticHandler)
     : Context(C), DiagnosticHandler(getDiagHandler(DiagnosticHandler, C)),
-      TheModule(nullptr), Buffer(nullptr), LazyStreamer(streamer),
-      NextUnreadBit(0), SeenValueSymbolTable(false), ValueList(C),
-      MDValueList(C), SeenFirstFunctionBody(false), UseRelativeIDs(false),
-      WillMaterializeAllForwardRefs(false), IsMetadataMaterialized(false) {}
+      TheModule(nullptr), Buffer(nullptr), Streamer(Streamer),
+      SeenValueSymbolTable(false), ValueList(C),
+      MDValueList(C), SeenFirstFunctionBody(false), UseRelativeIDs(false) {}
 
 std::error_code BitcodeReader::materializeForwardReferencedFunctions() {
   if (WillMaterializeAllForwardRefs)
     return std::error_code();
 
   // Prevent recursion.
   WillMaterializeAllForwardRefs = true;
 
static void UpgradeDLLImportExportLinkage(llvm::GlobalValue *GV, unsigned Val) {
   switch (Val) {
   case 5: GV->setDLLStorageClass(GlobalValue::DLLImportStorageClass); break;
   case 6: GV->setDLLStorageClass(GlobalValue::DLLExportStorageClass); break;
   }
 }
 
 namespace llvm {
 namespace {
-  /// @brief A class for maintaining the slot number definition
+  /// A class for maintaining the slot number definition
   /// as a placeholder for the actual definition for forward constants defs.
   class ConstantPlaceHolder : public ConstantExpr {
     void operator=(const ConstantPlaceHolder &) = delete;
   public:
-    // allocate space for exactly one operand
+    /// allocate space for exactly one operand
     void *operator new(size_t s) {
       return User::operator new(s, 1);
     }
     explicit ConstantPlaceHolder(Type *Ty, LLVMContext& Context)
       : ConstantExpr(Ty, Instruction::UserOp1, &Op<0>(), 1) {
       Op<0>() = UndefValue::get(Type::getInt32Ty(Context));
     }
 
-    /// @brief Methods to support type inquiry through isa, cast, and dyn_cast.
+    /// Methods to support type inquiry through isa, cast, and dyn_cast.
     static bool classof(const Value *V) {
       return isa<ConstantExpr>(V) &&
              cast<ConstantExpr>(V)->getOpcode() == Instruction::UserOp1;
     }
 
 
     /// Provide fast operand accessors
     DECLARE_TRANSPARENT_OPERAND_ACCESSORS(Value);
std::error_code BitcodeReader::GlobalCleanup() {
 
   // Force deallocation of memory for these vectors to favor the client that
   // want lazy deserialization.
   std::vector<std::pair<GlobalVariable*, unsigned> >().swap(GlobalInits);
   std::vector<std::pair<GlobalAlias*, unsigned> >().swap(AliasInits);
   return std::error_code();
 }
 
-std::error_code BitcodeReader::ParseModule(bool Resume,
-                                           bool ShouldLazyLoadMetadata) {
-  if (Resume)
-    Stream.JumpToBit(NextUnreadBit);
-  else if (Stream.EnterSubBlock(bitc::MODULE_BLOCK_ID))
+std::error_code BitcodeReader::ParseModule() {
+  if (ParseState == AtTopLevel) {
+    if (Stream.EnterSubBlock(bitc::MODULE_BLOCK_ID))
       return Error("Invalid record");
+    setParseState(InsideModule);
+  } else {
+    assert(ParseState == InsideModule);
+  }
 
   SmallVector<uint64_t, 64> Record;
   std::vector<std::string> SectionTable;
   std::vector<std::string> GCTable;
 
   // Read all the records for this module.
   while (1) {
     BitstreamEntry Entry = Stream.advance();
 
     switch (Entry.Kind) {
     case BitstreamEntry::Error:
       return Error("Malformed block");
     case BitstreamEntry::EndBlock:
+      setParseState(AtTopLevel);
       return GlobalCleanup();
 
     case BitstreamEntry::SubBlock:
       switch (Entry.ID) {
       default:  // Skip unknown content.
         if (Stream.SkipBlock())
           return Error("Invalid record");
         break;
case BitstreamEntry::SubBlock:
           std::reverse(FunctionsWithBodies.begin(), FunctionsWithBodies.end());
           if (std::error_code EC = GlobalCleanup())
             return EC;
           SeenFirstFunctionBody = true;
         }
 
         if (std::error_code EC = RememberAndSkipFunctionBody())
           return EC;
-        // For streaming bitcode, suspend parsing when we reach the function
-        // bodies. Subsequent materialization calls will resume it when
-        // necessary. For streaming, the function bodies must be at the end of
-        // the bitcode. If the bitcode file is old, the symbol table will be
-        // at the end instead and will not have been seen yet. In this case,
-        // just finish the parse now.
-        if (LazyStreamer && SeenValueSymbolTable) {
-          NextUnreadBit = Stream.GetCurrentBitNo();
+        // Suspend parsing when we reach a function body, assuming we
+        // have already associated names with global values. Note: If
+        // the bitcode file is old, the symbol table will be at the
+        // end instead and will not have been seen yet.
+        if (SeenValueSymbolTable)
           return std::error_code();
-        }
         break;
       case bitc::USELIST_BLOCK_ID:
         if (std::error_code EC = ParseUseLists())
           return EC;
         break;
       }
       continue;
 
     case BitstreamEntry::Record:
       // The interesting case.
       break;
     }
 
-
     // Read a record.
     switch (Stream.readRecord(Entry.ID, Record)) {
     default: break;  // Default behavior, ignore unknown content.
     case bitc::MODULE_CODE_VERSION: {  // VERSION: [version#]
       if (Record.size() < 1)
         return Error("Invalid record");
       // Only version #0 and #1 are supported so far.
       unsigned module_version = Record[0];
case bitc::MODULE_CODE_FUNCTION: {
 
       ValueList.push_back(Func);
 
       // If this is a function with a body, remember the prototype we are
       // creating now, so that we can match up the body with them later.
       if (!isProto) {
         Func->setIsMaterializable(true);
         FunctionsWithBodies.push_back(Func);
-        if (LazyStreamer)
-          DeferredFunctionInfo[Func] = 0;
       }
       break;
     }
     // ALIAS: [alias type, aliasee val#, linkage]
     // ALIAS: [alias type, aliasee val#, linkage, visibility, dllstorageclass]
     case bitc::MODULE_CODE_ALIAS: {
       if (Record.size() < 3)
         return Error("Invalid record");
case bitc::MODULE_CODE_PURGEVALS:
         return Error("Invalid record");
       ValueList.shrinkTo(Record[0]);
       break;
     }
     Record.clear();
   }
 }
 
-std::error_code BitcodeReader::ParseBitcodeInto(Module *M,
+std::error_code BitcodeReader::parseBitcodeInto(Module *M,
+                                                bool ShouldMaterializeAll,
                                                 bool ShouldLazyLoadMetadata) {
-  TheModule = nullptr;
+  auto cleanupOnError = [&](std::error_code EC) {
+    releaseBuffer(); // Never take ownership on error.
+    return EC;
+  };
+
+  TheModule = M;
+  this->ShouldLazyLoadMetadata = ShouldLazyLoadMetadata;
+
+  if (std::error_code EC =  startParse())
+    return cleanupOnError(EC);
+
+  if (ShouldMaterializeAll) {
+    if (std::error_code EC = materializeModule(TheModule))
+      return cleanupOnError(EC);
+  } else {
+    if (std::error_code EC = materializeForwardReferencedFunctions())
+      return cleanupOnError(EC);
+  }
+
+  return std::error_code();
+}
+
+std::error_code BitcodeReader::startParse() {
+  assert(ParseState == AtStart);
 
   if (std::error_code EC = InitStream())
     return EC;
 
   // Sniff for the signature.
   if (Stream.Read(8) != 'B' ||
       Stream.Read(8) != 'C' ||
       Stream.Read(4) != 0x0 ||
       Stream.Read(4) != 0xC ||
       Stream.Read(4) != 0xE ||
       Stream.Read(4) != 0xD)
     return Error("Invalid bitcode signature");
 
+  return continueParse();
+}
+
+std::error_code BitcodeReader::continueParse() {
+  switch (ParseState) {
+  case AtStart:
+    setParseState(AtTopLevel);
+    break;
+  case AtTopLevel:
+    // Restore input position to saved position on last call.
+    Stream.JumpToBit(NextUnreadBit);
+    break;
+  case InsideModule: {
+    // Restore input position to saved position on last call,
+    // and then continue parsing module.
+    Stream.JumpToBit(NextUnreadBit);
+    std::error_code EC = ParseModule();
+    setParseStateIfError(EC);
+    return EC;
+  }
+  case NoMoreInput:
+  case ReachedEof:
+  case FinishedParse:
+    return std::error_code();
+  case ParseError:
+    return Error("Can't continue, bitcode error already found");
+  }
+
   // We expect a number of well-defined blocks, though we don't necessarily
   // need to understand them all.
   while (1) {
+    assert(ParseState == AtTopLevel);
+
     if (Stream.AtEndOfStream()) {
-      if (TheModule)
-        return std::error_code();
-      // We didn't really read a proper Module.
-      return Error("Malformed IR file");
+      setParseState(ReachedEof);
     }
 
     BitstreamEntry Entry =
       Stream.advance(BitstreamCursor::AF_DontAutoprocessAbbrevs);
 
     switch (Entry.Kind) {
     case BitstreamEntry::Error:
-      return Error("Malformed block");
     case BitstreamEntry::EndBlock:
-      return std::error_code();
-
+      {
+        // Give bit address where error is found, so that it can be
+        // easily repaired if is in an invalid test file.
+        std::string Buffer;
+        raw_string_ostream StrBuf(Buffer);
+        uint64_t Bit = Stream.GetCurrentBitNo();
+        errs() << "Malformed IR file at bit " << format("%x", (Bit / CHAR_BIT))
+               << ":" << (Bit % CHAR_BIT);
+        return Error(StrBuf.str());
+      }
     case BitstreamEntry::SubBlock:
       switch (Entry.ID) {
       case bitc::BLOCKINFO_BLOCK_ID:
         if (Stream.ReadBlockInfoBlock())
           return Error("Malformed block");
         break;
-      case bitc::MODULE_BLOCK_ID:
+      case bitc::MODULE_BLOCK_ID: {
         // Reject multiple MODULE_BLOCK's in a single bitstream.
-        if (TheModule)
+        if (NumModulesParsed++)
           return Error("Invalid multiple blocks");
-        TheModule = M;
-        if (std::error_code EC = ParseModule(false, ShouldLazyLoadMetadata))
-          return EC;
-        if (LazyStreamer)
-          return std::error_code();
-        break;
+        std::error_code EC = ParseModule();
+        setParseStateIfError(EC);
+      }
       default:
         if (Stream.SkipBlock())
           return Error("Invalid record");
         break;
       }
       continue;
     case BitstreamEntry::Record:
       // There should be no records in the top-level of blocks.
 
       // The ranlib in Xcode 4 will align archive members by appending newlines
       // to the end of them. If this file size is a multiple of 4 but not 8, we
       // have to read and ignore these final 4 bytes :-(
       if (Stream.getAbbrevIDWidth() == 2 && Entry.ID == 2 &&
           Stream.Read(6) == 2 && Stream.Read(24) == 0xa0a0a &&
-          Stream.AtEndOfStream())
+          Stream.AtEndOfStream()) {
+        setParseState(ReachedEof);
         return std::error_code();
+      }
 
       return Error("Invalid record");
     }
   }
 }
 
+std::error_code BitcodeReader::finishParse() {
+  assert(TheModule);
+
+  while (ParseState < NoMoreInput) {
+    if (std::error_code EC = continueParse())
+      return EC;
+  }
+
+  switch (ParseState) {
+  case AtStart:
+  case AtTopLevel:
+  case InsideModule:
+    llvm_unreachable("finishParse exits with ParseState < NoMoreInput");
+  case NoMoreInput:
+  case ReachedEof:
+    setParseState(FinishedParse);
+    break;
+  case FinishedParse:
+    break;
+  case ParseError:
+    return Error("Can't continue, bitcode error already found");
+  }
+  if (NumModulesParsed == 1)
+    return std::error_code();
+  // We didn't really read a proper Module.
+  return Error("Malformed IR file");
+}
+
 ErrorOr<std::string> BitcodeReader::parseModuleTriple() {
   if (Stream.EnterSubBlock(bitc::MODULE_BLOCK_ID))
     return Error("Invalid record");
 
   SmallVector<uint64_t, 64> Record;
 
   std::string Triple;
   // Read all the records for this module.
OutOfRecordLoop:
   return std::error_code();
 }
 
 /// Find the function body in the bitcode stream
 std::error_code BitcodeReader::FindFunctionInStream(
     Function *F,
     DenseMap<Function *, uint64_t>::iterator DeferredFunctionInfoIterator) {
   while (DeferredFunctionInfoIterator->second == 0) {
-    if (Stream.AtEndOfStream())
+    if (ParseState >= NoMoreInput) {
       return Error("Could not find function in stream");
-    // ParseModule will parse the next body in the stream and set its
-    // position in the DeferredFunctionInfo map.
-    if (std::error_code EC = ParseModule(true))
+    }
+    if (std::error_code EC = continueParse()) {
       return EC;
     }
+  }
   return std::error_code();
 }
 
 //===----------------------------------------------------------------------===//
 // GVMaterializer implementation
 //===----------------------------------------------------------------------===//
 
 void BitcodeReader::releaseBuffer() { Buffer.release(); }
 
 std::error_code BitcodeReader::materialize(GlobalValue *GV) {
   if (std::error_code EC = materializeMetadata())
     return EC;
 
   Function *F = dyn_cast<Function>(GV);
   // If it's not a function or is already material, ignore the request.
   if (!F || !F->isMaterializable())
     return std::error_code();
 
   DenseMap<Function*, uint64_t>::iterator DFII = DeferredFunctionInfo.find(F);
   assert(DFII != DeferredFunctionInfo.end() && "Deferred function not found!");
   // If its position is recorded as 0, its body is somewhere in the stream
   // but we haven't seen it yet.
-  if (DFII->second == 0 && LazyStreamer)
+  if (DFII->second == 0)
     if (std::error_code EC = FindFunctionInStream(F, DFII))
       return EC;
 
   // Move the bit stream to the saved position of the deferred function body.
   Stream.JumpToBit(DFII->second);
 
   if (std::error_code EC = ParseFunctionBody(F))
     return EC;
if (I->first != I->second) {
         if (CallInst* CI = dyn_cast<CallInst>(*UI++))
           UpgradeIntrinsicCall(CI, I->second);
       }
     }
   }
 
   // Bring in any functions that this function forward-referenced via
   // blockaddresses.
   return materializeForwardReferencedFunctions();
 }
 
 bool BitcodeReader::isDematerializable(const GlobalValue *GV) const {
   const Function *F = dyn_cast<Function>(GV);
   if (!F || F->isDeclaration())
     return false;
 
   // Dematerializing F would leave dangling references that wouldn't be
void BitcodeReader::dematerialize(GlobalValue *GV) {
   F->dropAllReferences();
   F->setIsMaterializable(true);
 }
 
 std::error_code BitcodeReader::materializeModule(Module *M) {
   assert(M == TheModule &&
          "Can only Materialize the Module this BitcodeReader is attached to.");
 
-  if (std::error_code EC = materializeMetadata())
+  // Make sure the rest of the bits in the module (excluding materializable)
+  // have been read.
+  if (std::error_code EC = finishParse())
     return EC;
 
-  // Promise to materialize all forward references.
-  WillMaterializeAllForwardRefs = true;
+  if (std::error_code EC = materializeMetadata())
+    return EC;
 
   // Iterate over the module, deserializing any functions that are still on
   // disk.
   for (Module::iterator F = TheModule->begin(), E = TheModule->end();
        F != E; ++F) {
     if (std::error_code EC = materialize(F))
       return EC;
   }
-  // At this point, if there are any function bodies, the current bit is
-  // pointing to the END_BLOCK record after them. Now make sure the rest
-  // of the bits in the module have been read.
-  if (NextUnreadBit)
-    ParseModule(true);
 
-  // Check that all block address forward references got resolved (as we
-  // promised above).
+  // Check that all block address forward references got resolved.
   if (!BasicBlockFwdRefs.empty())
     return Error("Never resolved function from blockaddress");
 
   // Upgrade any intrinsic calls that slipped through (should not happen!) and
   // delete the old functions to clean up. We can't do this unless the entire
   // module is materialized because there could always be another function body
   // with calls to the old function.
   for (std::vector<std::pair<Function*, Function*> >::iterator I =
std::error_code BitcodeReader::materializeModule(Module *M) {
   return std::error_code();
 }
 
 std::vector<StructType *> BitcodeReader::getIdentifiedStructTypes() const {
   return IdentifiedStructTypes;
 }
 
 std::error_code BitcodeReader::InitStream() {
-  if (LazyStreamer)
+  if (Streamer)
     return InitLazyStream();
   return InitStreamFromBuffer();
 }
 
 std::error_code BitcodeReader::InitStreamFromBuffer() {
   const unsigned char *BufPtr = (const unsigned char*)Buffer->getBufferStart();
   const unsigned char *BufEnd = BufPtr+Buffer->getBufferSize();
 
std::error_code BitcodeReader::InitStreamFromBuffer() {
   Stream.init(&*StreamFile);
 
   return std::error_code();
 }
 
 std::error_code BitcodeReader::InitLazyStream() {
   // Check and strip off the bitcode wrapper; BitstreamReader expects never to
   // see it.
-  auto OwnedBytes = llvm::make_unique<StreamingMemoryObject>(LazyStreamer);
+  auto OwnedBytes = llvm::make_unique<StreamingMemoryObject>(Streamer);
   StreamingMemoryObject &Bytes = *OwnedBytes;
   StreamFile = llvm::make_unique<BitstreamReader>(std::move(OwnedBytes));
   Stream.init(&*StreamFile);
 
   unsigned char buf[16];
   if (Bytes.readBytes(buf, 16, 0) != 16)
     return Error("Invalid bitcode signature");
 
getLazyBitcodeModuleImpl(std::unique_ptr<MemoryBuffer> &&Buffer,
                          LLVMContext &Context, bool WillMaterializeAll,
                          DiagnosticHandlerFunction DiagnosticHandler,
                          bool ShouldLazyLoadMetadata = false) {
   Module *M = new Module(Buffer->getBufferIdentifier(), Context);
   BitcodeReader *R =
       new BitcodeReader(Buffer.get(), Context, DiagnosticHandler);
   M->setMaterializer(R);
 
-  auto cleanupOnError = [&](std::error_code EC) {
-    R->releaseBuffer(); // Never take ownership on error.
+  if (std::error_code EC =
+      R->parseBitcodeInto(M, WillMaterializeAll, ShouldLazyLoadMetadata)) {
     delete M;  // Also deletes R.
     return EC;
-  };
-
-  // Delay parsing Metadata if ShouldLazyLoadMetadata is true.
-  if (std::error_code EC = R->ParseBitcodeInto(M, ShouldLazyLoadMetadata))
-    return cleanupOnError(EC);
-
-  if (!WillMaterializeAll)
-    // Resolve forward references from blockaddresses.
-    if (std::error_code EC = R->materializeForwardReferencedFunctions())
-      return cleanupOnError(EC);
+  }
 
   Buffer.release(); // The BitcodeReader owns it now.
   return M;
 }
 
 ErrorOr<Module *>
 llvm::getLazyBitcodeModule(std::unique_ptr<MemoryBuffer> &&Buffer,
                            LLVMContext &Context,
                            DiagnosticHandlerFunction DiagnosticHandler,
                            bool ShouldLazyLoadMetadata) {
   return getLazyBitcodeModuleImpl(std::move(Buffer), Context, false,
                                   DiagnosticHandler, ShouldLazyLoadMetadata);
 }
 
 ErrorOr<std::unique_ptr<Module>>
 llvm::getStreamedBitcodeModule(StringRef Name, DataStreamer *Streamer,
                                LLVMContext &Context,
                                DiagnosticHandlerFunction DiagnosticHandler) {
   std::unique_ptr<Module> M = make_unique<Module>(Name, Context);
   BitcodeReader *R = new BitcodeReader(Streamer, Context, DiagnosticHandler);
   M->setMaterializer(R);
-  if (std::error_code EC = R->ParseBitcodeInto(M.get()))
+  if (std::error_code EC = R->parseBitcodeInto(M.get(), false, false))
     return EC;
   return std::move(M);
 }
 
 ErrorOr<Module *>
 llvm::parseBitcodeFile(MemoryBufferRef Buffer, LLVMContext &Context,
                        DiagnosticHandlerFunction DiagnosticHandler) {
   std::unique_ptr<MemoryBuffer> Buf = MemoryBuffer::getMemBuffer(Buffer, false);
   ErrorOr<Module *> ModuleOrErr = getLazyBitcodeModuleImpl(
       std::move(Buf), Context, true, DiagnosticHandler);
   if (!ModuleOrErr)
     return ModuleOrErr;
   Module *M = ModuleOrErr.get();
-  // Read in the entire module, and destroy the BitcodeReader.
-  if (std::error_code EC = M->materializeAllPermanently()) {
-    delete M;
-    return EC;
-  }
 
   // TODO: Restore the use-lists to the in-memory state when the bitcode was
   // written.  We must defer until the Module has been fully materialized.
 
   return M;
 }
 
 std::string