Bitcode: Decouple block info block state from reader.

As proposed on llvm-dev:
http://lists.llvm.org/pipermail/llvm-dev/2016-October/106630.html

Move block info block state to a new class, BitstreamBlockInfo.
Clients may set the block info for a particular cursor with the
BitstreamCursor::setBlockInfo() method.

At this point BitstreamReader is not much more than a container for an
ArrayRef<uint8_t>, so remove it and replace all uses with direct uses
of memory buffers.

Differential Revision: https://reviews.llvm.org/D26259

llvm-svn: 286207

2 files changed, 29 insertions, 35 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 658e6d227e5..a5f040bfa36 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -233,7 +233,7 @@ protected:
   BitcodeReaderBase(MemoryBuffer *Buffer) : Buffer(Buffer) {}
 
   std::unique_ptr<MemoryBuffer> Buffer;
-  std::unique_ptr<BitstreamReader> StreamFile;
+  BitstreamBlockInfo BlockInfo;
   BitstreamCursor Stream;
 
   std::error_code initStream();
@@ -256,8 +256,8 @@ std::error_code BitcodeReaderBase::initStream() {
     if (SkipBitcodeWrapperHeader(BufPtr, BufEnd, true))
       return error("Invalid bitcode wrapper header");
 
-  StreamFile.reset(new BitstreamReader(ArrayRef<uint8_t>(BufPtr, BufEnd)));
-  Stream.init(&*StreamFile);
+  Stream = BitstreamCursor(ArrayRef<uint8_t>(BufPtr, BufEnd));
+  Stream.setBlockInfo(&BlockInfo);
 
   return std::error_code();
 }
@@ -2211,8 +2211,7 @@ std::error_code BitcodeReader::parseMetadataStrings(ArrayRef<uint64_t> Record,
     return error("Invalid record: metadata strings corrupt offset");
 
   StringRef Lengths = Blob.slice(0, StringsOffset);
-  SimpleBitstreamCursor R(*StreamFile);
-  R.jumpToPointer(Lengths.begin());
+  SimpleBitstreamCursor R(Lengths);
 
   StringRef Strings = Blob.drop_front(StringsOffset);
   do {
@@ -3759,9 +3758,12 @@ std::error_code BitcodeReader::parseBitcodeVersion() {
   }
 }
 
-
 bool BitcodeReaderBase::readBlockInfo() {
-  return Stream.ReadBlockInfoBlock();
+  Optional<BitstreamBlockInfo> NewBlockInfo = Stream.ReadBlockInfoBlock();
+  if (!NewBlockInfo)
+    return true;
+  BlockInfo = std::move(*NewBlockInfo);
+  return false;
 }
 
 std::error_code BitcodeReader::parseModule(uint64_t ResumeBit,
diff --git a/llvm/lib/Bitcode/Reader/BitstreamReader.cpp b/llvm/lib/Bitcode/Reader/BitstreamReader.cpp
index 0b549f7550f..f1237069f7b 100644
--- a/llvm/lib/Bitcode/Reader/BitstreamReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitstreamReader.cpp
@@ -18,14 +18,6 @@ using namespace llvm;
 //  BitstreamCursor implementation
 //===----------------------------------------------------------------------===//
 
-void BitstreamCursor::freeState() {
-  // Free all the Abbrevs.
-  CurAbbrevs.clear();
-
-  // Free all the Abbrevs in the block scope.
-  BlockScope.clear();
-}
-
 /// EnterSubBlock - Having read the ENTER_SUBBLOCK abbrevid, enter
 /// the block, and return true if the block has an error.
 bool BitstreamCursor::EnterSubBlock(unsigned BlockID, unsigned *NumWordsP) {
@@ -34,10 +26,12 @@ bool BitstreamCursor::EnterSubBlock(unsigned BlockID, unsigned *NumWordsP) {
   BlockScope.back().PrevAbbrevs.swap(CurAbbrevs);
 
   // Add the abbrevs specific to this block to the CurAbbrevs list.
-  if (const BitstreamReader::BlockInfo *Info =
-          getBitStreamReader()->getBlockInfo(BlockID)) {
-    CurAbbrevs.insert(CurAbbrevs.end(), Info->Abbrevs.begin(),
-                      Info->Abbrevs.end());
+  if (BlockInfo) {
+    if (const BitstreamBlockInfo::BlockInfo *Info =
+            BlockInfo->getBlockInfo(BlockID)) {
+      CurAbbrevs.insert(CurAbbrevs.end(), Info->Abbrevs.begin(),
+                        Info->Abbrevs.end());
+    }
   }
 
   // Get the codesize of this block.
@@ -318,15 +312,14 @@ void BitstreamCursor::ReadAbbrevRecord() {
   CurAbbrevs.push_back(Abbv);
 }
 
-bool BitstreamCursor::ReadBlockInfoBlock() {
-  // We expect the client to read the block info block at most once.
-  if (getBitStreamReader()->hasBlockInfoRecords())
-    report_fatal_error("Duplicate read of block info block");
+Optional<BitstreamBlockInfo>
+BitstreamCursor::ReadBlockInfoBlock(bool ReadBlockInfoNames) {
+  if (EnterSubBlock(bitc::BLOCKINFO_BLOCK_ID)) return None;
 
-  if (EnterSubBlock(bitc::BLOCKINFO_BLOCK_ID)) return true;
+  BitstreamBlockInfo NewBlockInfo;
 
   SmallVector<uint64_t, 64> Record;
-  BitstreamReader::BlockInfo *CurBlockInfo = nullptr;
+  BitstreamBlockInfo::BlockInfo *CurBlockInfo = nullptr;
 
   // Read all the records for this module.
   while (true) {
@@ -335,9 +328,9 @@ bool BitstreamCursor::ReadBlockInfoBlock() {
     switch (Entry.Kind) {
     case llvm::BitstreamEntry::SubBlock: // Handled for us already.
     case llvm::BitstreamEntry::Error:
-      return true;
+      return None;
     case llvm::BitstreamEntry::EndBlock:
-      return false;
+      return std::move(NewBlockInfo);
     case llvm::BitstreamEntry::Record:
       // The interesting case.
       break;
@@ -345,7 +338,7 @@ bool BitstreamCursor::ReadBlockInfoBlock() {
 
     // Read abbrev records, associate them with CurBID.
     if (Entry.ID == bitc::DEFINE_ABBREV) {
-      if (!CurBlockInfo) return true;
+      if (!CurBlockInfo) return None;
       ReadAbbrevRecord();
 
       // ReadAbbrevRecord installs the abbrev in CurAbbrevs.  Move it to the
@@ -360,13 +353,12 @@ bool BitstreamCursor::ReadBlockInfoBlock() {
     switch (readRecord(Entry.ID, Record)) {
       default: break;  // Default behavior, ignore unknown content.
       case bitc::BLOCKINFO_CODE_SETBID:
-        if (Record.size() < 1) return true;
-        CurBlockInfo =
-            &getBitStreamReader()->getOrCreateBlockInfo((unsigned)Record[0]);
+        if (Record.size() < 1) return None;
+        CurBlockInfo = &NewBlockInfo.getOrCreateBlockInfo((unsigned)Record[0]);
         break;
       case bitc::BLOCKINFO_CODE_BLOCKNAME: {
-        if (!CurBlockInfo) return true;
-        if (getBitStreamReader()->isIgnoringBlockInfoNames())
+        if (!CurBlockInfo) return None;
+        if (!ReadBlockInfoNames)
           break; // Ignore name.
         std::string Name;
         for (unsigned i = 0, e = Record.size(); i != e; ++i)
@@ -375,8 +367,8 @@ bool BitstreamCursor::ReadBlockInfoBlock() {
         break;
       }
       case bitc::BLOCKINFO_CODE_SETRECORDNAME: {
-        if (!CurBlockInfo) return true;
-        if (getBitStreamReader()->isIgnoringBlockInfoNames())
+        if (!CurBlockInfo) return None;
+        if (!ReadBlockInfoNames)
           break; // Ignore name.
         std::string Name;
         for (unsigned i = 1, e = Record.size(); i != e; ++i)