Index: llvm/include/llvm/Bitcode/BitCodes.h
===================================================================
--- llvm/include/llvm/Bitcode/BitCodes.h
+++ llvm/include/llvm/Bitcode/BitCodes.h
@@ -73,8 +73,9 @@
 
     BLOCKINFO_CODE_SETBID        = 1, // SETBID: [blockid#]
     BLOCKINFO_CODE_BLOCKNAME     = 2, // BLOCKNAME: [name]
-    BLOCKINFO_CODE_SETRECORDNAME = 3  // BLOCKINFO_CODE_SETRECORDNAME:
+    BLOCKINFO_CODE_SETRECORDNAME = 3, // BLOCKINFO_CODE_SETRECORDNAME:
                                       //                             [id, name]
+    BLOCKINFO_CODE_DEPENDENCY    = 4, // DEPENDENCY: [bitno]
   };
 
 } // End bitc namespace
Index: llvm/include/llvm/Bitcode/BitstreamReader.h
===================================================================
--- llvm/include/llvm/Bitcode/BitstreamReader.h
+++ llvm/include/llvm/Bitcode/BitstreamReader.h
@@ -58,6 +58,11 @@
   /// information in the BlockInfo block. Only llvm-bcanalyzer uses this.
   bool IgnoreBlockInfoNames;
 
+  /// Tracks the bit number of the most recently read block info block. This is
+  /// used to interpret the BLOCKINFO_CODE_DEPENDENCY record which helps ensure
+  /// that block info blocks are read in dependency order.
+  uint64_t BlockInfoDependency = 0;
+
 public:
   BitstreamReader() : IgnoreBlockInfoNames(true) {
   }
@@ -114,6 +119,9 @@
     return BlockInfoRecords.back();
   }
 
+  uint64_t getBlockInfoDependency() const { return BlockInfoDependency; }
+  void setBlockInfoDependency(uint64_t B) { BlockInfoDependency = B; }
+
   /// Takes block info from the other bitstream reader.
   ///
   /// This is a "take" operation because BlockInfo records are non-trivial, and
Index: llvm/include/llvm/Bitcode/BitstreamWriter.h
===================================================================
--- llvm/include/llvm/Bitcode/BitstreamWriter.h
+++ llvm/include/llvm/Bitcode/BitstreamWriter.h
@@ -42,6 +42,11 @@
   /// selected BLOCK ID.
   unsigned BlockInfoCurBID;
 
+  /// Tracks the bit number of the most recently written block info block. This
+  /// is used to write the BLOCKINFO_CODE_DEPENDENCY record which helps ensure
+  /// that block info blocks are read in dependency order.
+  uint64_t BlockInfoDependency = 0;
+
   /// CurAbbrevs - Abbrevs installed at in this block.
   std::vector<IntrusiveRefCntPtr<BitCodeAbbrev>> CurAbbrevs;
 
@@ -509,8 +514,14 @@
 
   /// EnterBlockInfoBlock - Start emitting the BLOCKINFO_BLOCK.
   void EnterBlockInfoBlock(unsigned CodeWidth) {
+    uint64_t LastBlockInfoDependency = BlockInfoDependency;
+    BlockInfoDependency = GetCurrentBitNo();
+
     EnterSubblock(bitc::BLOCKINFO_BLOCK_ID, CodeWidth);
     BlockInfoCurBID = ~0U;
+    if (LastBlockInfoDependency)
+      EmitRecord(bitc::BLOCKINFO_CODE_DEPENDENCY,
+                 ArrayRef<uint64_t>{LastBlockInfoDependency});
   }
 private:
   /// SwitchToBlockID - If we aren't already talking about the specified block
Index: llvm/lib/Bitcode/Reader/BitstreamReader.cpp
===================================================================
--- llvm/lib/Bitcode/Reader/BitstreamReader.cpp
+++ llvm/lib/Bitcode/Reader/BitstreamReader.cpp
@@ -319,13 +319,12 @@
 }
 
 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");
+  uint64_t BlockInfoDependency = GetCurrentBitNo();
 
   if (EnterSubBlock(bitc::BLOCKINFO_BLOCK_ID)) return true;
 
   SmallVector<uint64_t, 64> Record;
+  uint64_t LastBlockInfoDependency = 0;
   BitstreamReader::BlockInfo *CurBlockInfo = nullptr;
 
   // Read all the records for this module.
@@ -337,6 +336,12 @@
     case llvm::BitstreamEntry::Error:
       return true;
     case llvm::BitstreamEntry::EndBlock:
+      // We expect the client to read block info blocks in dependency order.
+      if (getBitStreamReader()->getBlockInfoDependency() !=
+          LastBlockInfoDependency)
+        report_fatal_error(
+            "Duplicate or out of order read of block info block");
+      getBitStreamReader()->setBlockInfoDependency(BlockInfoDependency);
       return false;
     case llvm::BitstreamEntry::Record:
       // The interesting case.
@@ -359,6 +364,9 @@
     Record.clear();
     switch (readRecord(Entry.ID, Record)) {
       default: break;  // Default behavior, ignore unknown content.
+      case bitc::BLOCKINFO_CODE_DEPENDENCY:
+        LastBlockInfoDependency = Record[0];
+        break;
       case bitc::BLOCKINFO_CODE_SETBID:
         if (Record.size() < 1) return true;
         CurBlockInfo =