diff --git a/llvm/include/llvm/Bitstream/BitCodes.h b/llvm/include/llvm/Bitstream/BitCodes.h
--- a/llvm/include/llvm/Bitstream/BitCodes.h
+++ b/llvm/include/llvm/Bitstream/BitCodes.h
@@ -40,11 +40,12 @@
     VBR   = 2,  // A VBR field where Val specifies the width of each chunk.
     Array = 3,  // A sequence of fields, next field species elt encoding.
     Char6 = 4,  // A 6-bit fixed field which maps to [a-zA-Z0-9._].
-    Blob  = 5   // 32-bit aligned array of 8-bit characters.
+    Blob  = 5,  // 32-bit aligned array of 8-bit characters.
+    VBRZ  = 6,  // A nullable VBR field, Val specifies the width of each chunk.
   };
 
   static bool isValidEncoding(uint64_t E) {
-    return E >= 1 && E <= 5;
+    return E >= 1 && E <= 6;
   }
 
   explicit BitCodeAbbrevOp(uint64_t V) :  Val(V), IsLiteral(true) {}
@@ -69,6 +70,7 @@
     switch (E) {
     case Fixed:
     case VBR:
+    case VBRZ:
       return true;
     case Array:
     case Char6:
diff --git a/llvm/include/llvm/Bitstream/BitstreamReader.h b/llvm/include/llvm/Bitstream/BitstreamReader.h
--- a/llvm/include/llvm/Bitstream/BitstreamReader.h
+++ b/llvm/include/llvm/Bitstream/BitstreamReader.h
@@ -226,7 +226,15 @@
     return R;
   }
 
-  Expected<uint32_t> ReadVBR(const unsigned NumBits) {
+  Expected<uint32_t> ReadVBR(const unsigned NumBits, bool ZeroBit = false) {
+    if (ZeroBit) {
+      Expected<unsigned> MaybeRead = Read(1);
+      if (!MaybeRead)
+        return MaybeRead;
+      if (*MaybeRead == 0)
+        return 0;
+    }
+
     Expected<unsigned> MaybeRead = Read(NumBits);
     if (!MaybeRead)
       return MaybeRead;
@@ -261,8 +269,16 @@
 
   // Read a VBR that may have a value up to 64-bits in size. The chunk size of
   // the VBR must still be <= 32 bits though.
-  Expected<uint64_t> ReadVBR64(const unsigned NumBits) {
-    Expected<uint64_t> MaybeRead = Read(NumBits);
+  Expected<uint64_t> ReadVBR64(const unsigned NumBits, bool ZeroBit = false) {
+    if (ZeroBit) {
+      Expected<unsigned> MaybeRead = Read(1);
+      if (!MaybeRead)
+        return MaybeRead;
+      if (*MaybeRead == 0)
+        return 0;
+    }
+
+    Expected<unsigned> MaybeRead = Read(NumBits);
     if (!MaybeRead)
       return MaybeRead;
     uint32_t Piece = MaybeRead.get();
diff --git a/llvm/include/llvm/Bitstream/BitstreamWriter.h b/llvm/include/llvm/Bitstream/BitstreamWriter.h
--- a/llvm/include/llvm/Bitstream/BitstreamWriter.h
+++ b/llvm/include/llvm/Bitstream/BitstreamWriter.h
@@ -221,7 +221,13 @@
     }
   }
 
-  void EmitVBR(uint32_t Val, unsigned NumBits) {
+  void EmitVBR(uint32_t Val, unsigned NumBits, bool ZeroBit = false) {
+    if (ZeroBit) {
+      Emit(Val != 0, 1);
+      if (Val == 0)
+        return;
+    }
+
     assert(NumBits <= 32 && "Too many bits to emit!");
     uint32_t Threshold = 1U << (NumBits-1);
 
@@ -234,10 +240,16 @@
     Emit(Val, NumBits);
   }
 
-  void EmitVBR64(uint64_t Val, unsigned NumBits) {
+  void EmitVBR64(uint64_t Val, unsigned NumBits, bool ZeroBit = false) {
     assert(NumBits <= 32 && "Too many bits to emit!");
     if ((uint32_t)Val == Val)
-      return EmitVBR((uint32_t)Val, NumBits);
+      return EmitVBR((uint32_t)Val, NumBits, ZeroBit);
+
+    if (ZeroBit) {
+      Emit(Val != 0, 1);
+      if (Val == 0)
+        return;
+    }
 
     uint32_t Threshold = 1U << (NumBits-1);
 
@@ -357,6 +369,10 @@
       if (Op.getEncodingData())
         EmitVBR64(V, (unsigned)Op.getEncodingData());
       break;
+    case BitCodeAbbrevOp::VBRZ:
+      if (Op.getEncodingData())
+        EmitVBR64(V, (unsigned)Op.getEncodingData(), /*ZeroBit=*/true);
+      break;
     case BitCodeAbbrevOp::Char6:
       Emit(BitCodeAbbrevOp::EncodeChar6((char)V), 6);
       break;
@@ -491,7 +507,7 @@
       EmitVBR(Code, 6);
       EmitVBR(Count, 6);
       for (unsigned i = 0, e = Count; i != e; ++i)
-        EmitVBR64(Vals[i], 6);
+        EmitVBR64(Vals[i], 6, /*ZeroBit=*/true);
       return;
     }
 
diff --git a/llvm/lib/Bitstream/Reader/BitstreamReader.cpp b/llvm/lib/Bitstream/Reader/BitstreamReader.cpp
--- a/llvm/lib/Bitstream/Reader/BitstreamReader.cpp
+++ b/llvm/lib/Bitstream/Reader/BitstreamReader.cpp
@@ -82,6 +82,9 @@
   case BitCodeAbbrevOp::VBR:
     assert((unsigned)Op.getEncodingData() <= Cursor.MaxChunkSize);
     return Cursor.ReadVBR64((unsigned)Op.getEncodingData());
+  case BitCodeAbbrevOp::VBRZ:
+    assert((unsigned)Op.getEncodingData() <= Cursor.MaxChunkSize);
+    return Cursor.ReadVBR64((unsigned)Op.getEncodingData(), /*ZeroBit=*/true);
   case BitCodeAbbrevOp::Char6:
     if (Expected<unsigned> Res = Cursor.Read(6))
       return BitCodeAbbrevOp::DecodeChar6(Res.get());
@@ -104,7 +107,7 @@
       return MaybeVBR.takeError();
     unsigned NumElts = MaybeVBR.get();
     for (unsigned i = 0; i != NumElts; ++i)
-      if (Expected<uint64_t> Res = ReadVBR64(6))
+      if (Expected<uint64_t> Res = ReadVBR64(6, /*ZeroBit=*/true))
         ; // Skip!
       else
         return Res.takeError();
@@ -169,10 +172,12 @@
           return std::move(Err);
         break;
       case BitCodeAbbrevOp::VBR:
+      case BitCodeAbbrevOp::VBRZ:
         assert((unsigned)EltEnc.getEncodingData() <= MaxChunkSize);
         for (; NumElts; --NumElts)
-          if (Expected<uint64_t> Res =
-                  ReadVBR64((unsigned)EltEnc.getEncodingData()))
+          if (Expected<uint64_t> Res = ReadVBR64(
+                  (unsigned)EltEnc.getEncodingData(),
+                  /*ZeroBit=*/EltEnc.getEncoding() == BitCodeAbbrevOp::VBRZ))
             ; // Skip!
           else
             return Res.takeError();
@@ -229,7 +234,7 @@
     Vals.reserve(Vals.size() + NumElts);
 
     for (unsigned i = 0; i != NumElts; ++i)
-      if (Expected<uint64_t> MaybeVal = ReadVBR64(6))
+      if (Expected<uint64_t> MaybeVal = ReadVBR64(6, /*ZeroBit=*/true))
         Vals.push_back(MaybeVal.get());
       else
         return MaybeVal.takeError();
@@ -306,9 +311,11 @@
             return MaybeVal.takeError();
         break;
       case BitCodeAbbrevOp::VBR:
+      case BitCodeAbbrevOp::VBRZ:
         for (; NumElts; --NumElts)
-          if (Expected<uint64_t> MaybeVal =
-                  ReadVBR64((unsigned)EltEnc.getEncodingData()))
+          if (Expected<uint64_t> MaybeVal = ReadVBR64(
+                  (unsigned)EltEnc.getEncodingData(),
+                  /*ZeroBit=*/EltEnc.getEncoding() == BitCodeAbbrevOp::VBRZ))
             Vals.push_back(MaybeVal.get());
           else
             return MaybeVal.takeError();