Make abbreviations explicit in pnacl-freeze/thaw.

include/llvm/Bitcode/NaCl/NaClBitstreamWriter.h

Index: include/llvm/Bitcode/NaCl/NaClBitstreamWriter.h
diff --git a/include/llvm/Bitcode/NaCl/NaClBitstreamWriter.h b/include/llvm/Bitcode/NaCl/NaClBitstreamWriter.h
index 26d9cb6b2486bc3d76c32f3a2b33d7ee633ac67e..c23fdc2f91e2b81f251f5dbd771c642a4c66a103 100644
--- a/include/llvm/Bitcode/NaCl/NaClBitstreamWriter.h
+++ b/include/llvm/Bitcode/NaCl/NaClBitstreamWriter.h
@@ -33,7 +33,7 @@ class NaClBitstreamWriter {
 
   /// CurCodeSize - This is the declared size of code values used for the
   /// current block, in bits.
-  unsigned CurCodeSize;
+  NaClBitcodeSelectorAbbrev CurCodeSize;
 
   /// BlockInfoCurBID - When emitting a BLOCKINFO_BLOCK, this is the currently
   /// selected BLOCK ID.
@@ -43,10 +43,11 @@ class NaClBitstreamWriter {
   std::vector<NaClBitCodeAbbrev*> CurAbbrevs;
 
   struct Block {
-    unsigned PrevCodeSize;
+    NaClBitcodeSelectorAbbrev PrevCodeSize;
     unsigned StartSizeWord;
     std::vector<NaClBitCodeAbbrev*> PrevAbbrevs;
-    Block(unsigned PCS, unsigned SSW) : PrevCodeSize(PCS), StartSizeWord(SSW) {}
+    Block(const NaClBitcodeSelectorAbbrev& PCS, unsigned SSW)
+        : PrevCodeSize(PCS), StartSizeWord(SSW) {}
   };
 
   /// BlockScope - This tracks the current blocks that we have entered.
@@ -94,7 +95,7 @@ class NaClBitstreamWriter {
 
 public:
   explicit NaClBitstreamWriter(SmallVectorImpl<char> &O)
-    : Out(O), CurBit(0), CurValue(0), CurCodeSize(2) {}
+      : Out(O), CurBit(0), CurValue(0), CurCodeSize() {}
 
   ~NaClBitstreamWriter() {
     assert(CurBit == 0 && "Unflused data remaining");
@@ -137,6 +138,10 @@ public:
     CurBit = (CurBit+NumBits) & 31;
   }
 
+  void EmitBool(bool b) {

[Karl, 2013/05/20 22:59:20]

Deleting this, since it is no longer needed.

+    Emit((uint32_t) b, 1);
+  }
+
   void Emit64(uint64_t Val, unsigned NumBits) {
     if (NumBits <= 32)
       Emit((uint32_t)Val, NumBits);
@@ -156,6 +161,7 @@ public:
 
   void EmitVBR(uint32_t Val, unsigned NumBits) {
     assert(NumBits <= 32 && "Too many bits to emit!");
+    assert(NumBits > 1 && "Too few bits to emit!");
     uint32_t Threshold = 1U << (NumBits-1);
 
     // Emit the bits with VBR encoding, NumBits-1 bits at a time.
@@ -169,6 +175,7 @@ public:
 
   void EmitVBR64(uint64_t Val, unsigned NumBits) {
     assert(NumBits <= 32 && "Too many bits to emit!");
+    assert(NumBits > 1 && "Too few bits to emit!");
     if ((uint32_t)Val == Val)
       return EmitVBR((uint32_t)Val, NumBits);
 
@@ -186,7 +193,10 @@ public:
 
   /// EmitCode - Emit the specified code.
   void EmitCode(unsigned Val) {
-    Emit(Val, CurCodeSize);
+    if (CurCodeSize.IsFixed)
+      Emit(Val, CurCodeSize.NumBits);
+    else
+      EmitVBR(Val, CurCodeSize.NumBits);
   }
 
   //===--------------------------------------------------------------------===//
@@ -207,16 +217,20 @@ public:
     return 0;
   }
 
-  void EnterSubblock(unsigned BlockID, unsigned CodeLen) {
+  // Enter block using CodeLen bits to read the size of the code selector
+  // associated with the block.
+  void EnterSubblock(unsigned BlockID,
+                     const NaClBitcodeSelectorAbbrev& CodeLen) {
     // Block header:
     //    [ENTER_SUBBLOCK, blockid, newcodelen, <align4bytes>, blocklen]
     EmitCode(naclbitc::ENTER_SUBBLOCK);
     EmitVBR(BlockID, naclbitc::BlockIDWidth);
-    EmitVBR(CodeLen, naclbitc::CodeLenWidth);
+    EmitBool(CodeLen.IsFixed);

[jvoung (off chromium), 2013/05/17 23:40:48]

See below:  if the fixedabbrevcutoff variant isn't used, then there's no need to
deviate from upstream and end up with an extra EmitBool here?

[Karl, 2013/05/20 22:59:20]

Deleted.

+    EmitVBR(CodeLen.NumBits, naclbitc::CodeLenWidth);
     FlushToWord();
 
     unsigned BlockSizeWordIndex = GetWordIndex();
-    unsigned OldCodeSize = CurCodeSize;
+    NaClBitcodeSelectorAbbrev OldCodeSize(CurCodeSize);
 
     // Emit a placeholder, which will be replaced when the block is popped.
     Emit(0, naclbitc::BlockSizeWidth);
@@ -239,6 +253,28 @@ public:
     }
   }
 
+  // Enter block with no abbreviations.
+  void EnterSubblock(unsigned BlockID) {
+    NaClBitcodeSelectorAbbrev DefaultCodeLen;
+    EnterSubblock(BlockID, DefaultCodeLen);
+  }
+
+  // Enter block with the given number of abbreviations.
+  void EnterSubblock(unsigned BlockID, unsigned NumAbbrev) {
+    NaClBitcodeSelectorAbbrev CodeLenAbbrev(NumAbbrev);
+    EnterSubblock(BlockID, CodeLenAbbrev);
+  }
+
+  // Enter block with the given number of abbreviations NumAbbrev,
+  // with the constraint that all abbreviations < FixedAbbrevCutoff will
+  // be read using a single read.
+  void EnterSubblock(unsigned BlockId,

[jvoung (off chromium), 2013/05/17 23:40:48]

Is this actually used?

[Karl, 2013/05/20 22:59:20]

Again, I'm over planning changes. Removing this case, since it is not yet
necessary.

+                     unsigned NumAbbrev,
+                     unsigned FixedAbbrevCutoff) {
+    NaClBitcodeSelectorAbbrev CodeLenAbbrev(FixedAbbrevCutoff, NumAbbrev);
+    EnterSubblock(BlockId, CodeLenAbbrev);
+  }
+
   void ExitBlock() {
     assert(!BlockScope.empty() && "Block scope imbalance!");
 
@@ -501,8 +537,8 @@ public:
   //===--------------------------------------------------------------------===//
 
   /// EnterBlockInfoBlock - Start emitting the BLOCKINFO_BLOCK.
-  void EnterBlockInfoBlock(unsigned CodeWidth) {
-    EnterSubblock(naclbitc::BLOCKINFO_BLOCK_ID, CodeWidth);
+  void EnterBlockInfoBlock() {
+    EnterSubblock(naclbitc::BLOCKINFO_BLOCK_ID);
     BlockInfoCurBID = ~0U;
   }
 private: