Bitcode: Simplify BitstreamWriter::EnterBlockInfoBlock() interface.

[pcc]

Summary

No block info block should need to define local abbreviations, so we can
always use a code width of 2.

Also change all block info block writers to use EnterBlockInfoBlock.

[mehdi_amini]

Motivation is just serialization size here, right?

[pcc]

I am about to make EnterBlockInfoBlock more complicated in order to deal with multiple block info blocks, so I need all block info block writers to go through this function. The code width thing is just something I noticed in passing.

[mehdi_amini]

OK, so no particular motivation other than cleanup IIUC.

LGTM, thks.

clang/lib/Frontend/SerializedDiagnosticPrinter.cpp

 }
 
 static void AddRangeLocationAbbrev(llvm::BitCodeAbbrev *Abbrev) {
   AddSourceLocationAbbrev(Abbrev);
   AddSourceLocationAbbrev(Abbrev);  
 }
 
 void SDiagsWriter::EmitBlockInfoBlock() {
-  State->Stream.EnterBlockInfoBlock(3);
+  State->Stream.EnterBlockInfoBlock();
 
   using namespace llvm;
   llvm::BitstreamWriter &Stream = State->Stream;
   RecordData &Record = State->Record;
   AbbreviationMap &Abbrevs = State->Abbrevs;
 
   // ==---------------------------------------------------------------------==//
   // The subsequent records and Abbrevs are for the "Meta" block.

clang/lib/Serialization/ASTWriter.cpp

#define RECORD(X) EmitRecordID(X, #X, Stream, Record)
   RECORD(EXPR_CXX_UUIDOF_EXPR);
   RECORD(EXPR_CXX_UUIDOF_TYPE);
   RECORD(EXPR_LAMBDA);
 #undef RECORD
 }
 
 void ASTWriter::WriteBlockInfoBlock() {
   RecordData Record;
-  Stream.EnterSubblock(llvm::bitc::BLOCKINFO_BLOCK_ID, 3);
+  Stream.EnterBlockInfoBlock();
 
 #define BLOCK(X) EmitBlockID(X ## _ID, #X, Stream, Record)
 #define RECORD(X) EmitRecordID(X, #X, Stream, Record)
 
   // Control Block.
   BLOCK(CONTROL_BLOCK);
   RECORD(METADATA);
   RECORD(SIGNATURE);

clang/lib/Serialization/GlobalModuleIndex.cpp

static void emitRecordID(unsigned ID, const char *Name,
   while (*Name)
     Record.push_back(*Name++);
   Stream.EmitRecord(llvm::bitc::BLOCKINFO_CODE_SETRECORDNAME, Record);
 }
 
 void
 GlobalModuleIndexBuilder::emitBlockInfoBlock(llvm::BitstreamWriter &Stream) {
   SmallVector<uint64_t, 64> Record;
-  Stream.EnterSubblock(llvm::bitc::BLOCKINFO_BLOCK_ID, 3);
+  Stream.EnterBlockInfoBlock();
 
 #define BLOCK(X) emitBlockID(X ## _ID, #X, Stream, Record)
 #define RECORD(X) emitRecordID(X, #X, Stream, Record)
   BLOCK(GLOBAL_INDEX_BLOCK);
   RECORD(INDEX_METADATA);
   RECORD(MODULE);
   RECORD(IDENTIFIER_INDEX);
 #undef RECORD

llvm/include/llvm/Bitcode/BitstreamWriter.h

return static_cast<unsigned>(CurAbbrevs.size())-1 +
       bitc::FIRST_APPLICATION_ABBREV;
   }
 
   //===--------------------------------------------------------------------===//
   // BlockInfo Block Emission
   //===--------------------------------------------------------------------===//
 
   /// EnterBlockInfoBlock - Start emitting the BLOCKINFO_BLOCK.
-  void EnterBlockInfoBlock(unsigned CodeWidth) {
-    EnterSubblock(bitc::BLOCKINFO_BLOCK_ID, CodeWidth);
+  void EnterBlockInfoBlock() {
+    EnterSubblock(bitc::BLOCKINFO_BLOCK_ID, 2);
     BlockInfoCurBID = ~0U;
   }
 private:
   /// SwitchToBlockID - If we aren't already talking about the specified block
   /// ID, emit a BLOCKINFO_CODE_SETBID record.
   void SwitchToBlockID(unsigned BlockID) {
     if (BlockInfoCurBID == BlockID) return;
     SmallVector<unsigned, 2> V;

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

void ModuleBitcodeWriter::writeFunction(
   Stream.ExitBlock();
 }
 
 // Emit blockinfo, which defines the standard abbreviations etc.
 void ModuleBitcodeWriter::writeBlockInfo() {
   // We only want to emit block info records for blocks that have multiple
   // instances: CONSTANTS_BLOCK, FUNCTION_BLOCK and VALUE_SYMTAB_BLOCK.
   // Other blocks can define their abbrevs inline.
-  Stream.EnterBlockInfoBlock(2);
+  Stream.EnterBlockInfoBlock();
 
   { // 8-bit fixed-width VST_CODE_ENTRY/VST_CODE_BBENTRY strings.
     BitCodeAbbrev *Abbv = new BitCodeAbbrev();
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 3));
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
     Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 8));
     if (Stream.EmitBlockInfoAbbrev(bitc::VALUE_SYMTAB_BLOCK_ID, Abbv) !=