Add an index for Module Metadata record in the bitcode

Summary:
This index record the position for each metadata record in
the bitcode, so that the reader will be able to lazy-load
on demand each individual record.

We also make sure that every abbrev is emitted upfront so
that the block can be skipped while reading.

I don't plan to commit this before having the reader
counterpart, but I figured this can be reviewed mostly
independently.

Reviewers: pcc, tejohnson

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D28083

llvm-svn: 290684

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp b/llvm/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
index e494343bf87..3220063275b 100644
--- a/llvm/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
+++ b/llvm/tools/llvm-bcanalyzer/llvm-bcanalyzer.cpp
@@ -353,6 +353,8 @@ static const char *GetCodeName(unsigned CodeID, unsigned BlockID,
       STRINGIFY_CODE(METADATA, OBJC_PROPERTY)
       STRINGIFY_CODE(METADATA, IMPORTED_ENTITY)
       STRINGIFY_CODE(METADATA, MODULE)
+      STRINGIFY_CODE(METADATA, INDEX_OFFSET)
+      STRINGIFY_CODE(METADATA, INDEX)
     }
   case bitc::METADATA_KIND_BLOCK_ID:
     switch (CodeID) {
@@ -514,6 +516,9 @@ static bool ParseBlock(BitstreamCursor &Stream, BitstreamBlockInfo &BlockInfo,
 
   SmallVector<uint64_t, 64> Record;
 
+  // Keep the offset to the metadata index if seen.
+  uint64_t MetadataIndexOffset = 0;
+
   // Read all the records for this block.
   while (1) {
     if (Stream.AtEndOfStream())
@@ -600,6 +605,22 @@ static bool ParseBlock(BitstreamCursor &Stream, BitstreamBlockInfo &BlockInfo,
       for (unsigned i = 0, e = Record.size(); i != e; ++i)
         outs() << " op" << i << "=" << (int64_t)Record[i];
 
+      // If we found a metadata index, let's verify that we had an offset before
+      // and validate its forward reference offset was correct!
+      if (BlockID == bitc::METADATA_BLOCK_ID) {
+        if (Code == bitc::METADATA_INDEX_OFFSET) {
+          MetadataIndexOffset = Stream.GetCurrentBitNo() + Record[0];
+        }
+        if (Code == bitc::METADATA_INDEX) {
+          outs() << " (offset ";
+          if (MetadataIndexOffset == RecordStartBit)
+            outs() << "match)";
+          else
+            outs() << "mismatch: " << MetadataIndexOffset << " vs "
+                   << RecordStartBit << ")";
+        }
+      }
+
       // If we found a module hash, let's verify that it matches!
       if (BlockID == bitc::MODULE_BLOCK_ID && Code == bitc::MODULE_CODE_HASH) {
         if (Record.size() != 5)