From cbbb09687f563fad96fd815a3a89920f436373e4 Mon Sep 17 00:00:00 2001
From: Chad Rosier <mcrosier@apple.com>
Date: Wed, 7 Dec 2011 21:44:12 +0000
Subject: Begin adding experimental support for preserving use-list ordering of
 bitcode files.  First, add a new block USELIST_BLOCK to the bitcode format. 
 This is where USELIST_CODE_ENTRYs will be stored.  The format of the
 USELIST_CODE_ENTRYs have not yet been defined.  Add support in the
 BitcodeReader for parsing the USELIST_BLOCK. Part of rdar://9860654 and
 PR5680.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146078 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Bitcode/Reader/BitcodeReader.cpp | 51 ++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

(limited to 'lib/Bitcode/Reader/BitcodeReader.cpp')

diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index 3682e6ddca..d584015ef8 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1287,6 +1287,50 @@ bool BitcodeReader::ParseConstants() {
   return false;
 }
 
+bool BitcodeReader::ParseUseLists() {
+  if (Stream.EnterSubBlock(bitc::USELIST_BLOCK_ID))
+    return Error("Malformed block record");
+
+  SmallVector<uint64_t, 64> Record;
+  
+  // Read all the records.
+  while (1) {
+    unsigned Code = Stream.ReadCode();
+    if (Code == bitc::END_BLOCK) {
+      if (Stream.ReadBlockEnd())
+        return Error("Error at end of use-list table block");
+      return false;
+    }
+    
+    if (Code == bitc::ENTER_SUBBLOCK) {
+      // No known subblocks, always skip them.
+      Stream.ReadSubBlockID();
+      if (Stream.SkipBlock())
+        return Error("Malformed block record");
+      continue;
+    }
+    
+    if (Code == bitc::DEFINE_ABBREV) {
+      Stream.ReadAbbrevRecord();
+      continue;
+    }
+    
+    // Read a use list record.
+    Record.clear();
+    switch (Stream.ReadRecord(Code, Record)) {
+    default:  // Default behavior: unknown type.
+      break;
+    case bitc::USELIST_CODE_ENTRY: { // USELIST_CODE_ENTRY: TBD.
+      unsigned RecordLength = Record.size();
+      if (RecordLength < 1)
+        return Error ("Invalid UseList reader!");
+      UseListRecords.push_back(Record);
+      break;
+    }
+    }
+  }
+}
+
 /// RememberAndSkipFunctionBody - When we see the block for a function body,
 /// remember where it is and then skip it.  This lets us lazily deserialize the
 /// functions.
@@ -1393,6 +1437,10 @@ bool BitcodeReader::ParseModule() {
         if (RememberAndSkipFunctionBody())
           return true;
         break;
+      case bitc::USELIST_BLOCK_ID:
+        if (ParseUseLists())
+          return true;
+        break;
       }
       continue;
     }
@@ -2746,6 +2794,9 @@ Module *llvm::ParseBitcodeFile(MemoryBuffer *Buffer, LLVMContext& Context,
     return 0;
   }
 
+  // TODO: Restore the use-lists to the in-memory state when the bitcode was
+  // written.  We must defer until the Module has been fully materialized.
+
   return M;
 }
 
-- 
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