Bitcode: Correctly handle Fixed and VBR arrays in BitstreamCursor::skipRecord().

[pcc]

Summary

The assertions were wrong; we need to call getEncodingData() on the element,
not the array. While here, simplify the skipRecord() implementation for Fixed
and Char6 arrays. This is tested by the code I added to llvm-bcanalyzer
which makes sure that we can skip any record.

[mehdi_amini]

LGTM!

llvm/lib/Bitcode/Reader/BitstreamReader.cpp

if (Op.getEncoding() == BitCodeAbbrevOp::Array) {
       const BitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i);
 
       // Read all the elements.
       // Decode the value as we are commanded.
       switch (EltEnc.getEncoding()) {
       default:
         report_fatal_error("Array element type can't be an Array or a Blob");
       case BitCodeAbbrevOp::Fixed:
-        assert((unsigned)Op.getEncodingData() <= MaxChunkSize);
-        for (; NumElts; --NumElts)
-          Read((unsigned)EltEnc.getEncodingData());
+        assert((unsigned)EltEnc.getEncodingData() <= MaxChunkSize);
+        JumpToBit(GetCurrentBitNo() + NumElts * EltEnc.getEncodingData());
         break;
       case BitCodeAbbrevOp::VBR:
-        assert((unsigned)Op.getEncodingData() <= MaxChunkSize);
+        assert((unsigned)EltEnc.getEncodingData() <= MaxChunkSize);
         for (; NumElts; --NumElts)
           ReadVBR64((unsigned)EltEnc.getEncodingData());
         break;
       case BitCodeAbbrevOp::Char6:
-        for (; NumElts; --NumElts)
-          Read(6);
+        JumpToBit(GetCurrentBitNo() + NumElts * 6);
         break;
       }
       continue;
     }
 
     assert(Op.getEncoding() == BitCodeAbbrevOp::Blob);
     // Blob case.  Read the number of bytes as a vbr6.
     unsigned NumElts = ReadVBR(6);

llvm/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp

if (Entry.ID == bitc::DEFINE_ABBREV) {
       continue;
     }
     
     Record.clear();
 
     ++BlockStats.NumRecords;
 
     StringRef Blob;
-    unsigned CurrentRecordPos = Stream.getCurrentByteNo();
+    unsigned CurrentRecordPos = Stream.GetCurrentBitNo();
     unsigned Code = Stream.readRecord(Entry.ID, Record, &Blob);
 
     // Increment the # occurrences of this code.
     if (BlockStats.CodeFreq.size() <= Code)
       BlockStats.CodeFreq.resize(Code+1);
     BlockStats.CodeFreq[Code].NumInstances++;
     BlockStats.CodeFreq[Code].TotalBits +=
       Stream.GetCurrentBitNo()-RecordStartBit;
if (DumpRecords) {
       if (BlockID == bitc::MODULE_BLOCK_ID && Code == bitc::MODULE_CODE_HASH) {
         if (Record.size() != 5)
           outs() << " (invalid)";
         else {
           // Recompute the hash and compare it to the one in the bitcode
           SHA1 Hasher;
           StringRef Hash;
           {
-            int BlockSize = CurrentRecordPos - BlockEntryPos;
+            int BlockSize = (CurrentRecordPos / 8) - BlockEntryPos;
             auto Ptr = Stream.getPointerToByte(BlockEntryPos, BlockSize);
             Hasher.update(ArrayRef<uint8_t>(Ptr, BlockSize));
             Hash = Hasher.result();
           }
           SmallString<20> RecordedHash;
           RecordedHash.resize(20);
           int Pos = 0;
           for (auto &Val : Record) {
if (DumpRecords) {
             outs() << "'" << Blob << "'";
           else
             outs() << "unprintable, " << Blob.size() << " bytes.";          
         }
       }
 
       outs() << "\n";
     }
+
+    // Make sure that we can skip the current record.
+    Stream.JumpToBit(CurrentRecordPos);
+    Stream.skipRecord(Entry.ID);
   }
 }
 
 static void PrintSize(double Bits) {
   outs() << format("%.2f/%.2fB/%luW", Bits, Bits/8,(unsigned long)(Bits/32));
 }
 static void PrintSize(uint64_t Bits) {
   outs() << format("%lub/%.2fB/%luW", (unsigned long)Bits,