[CodeView] Fix cycles in debug info when merging Types with global hashes

When type streams with forward references were merged using GHashes, cycles 
were introduced in the debug info. This was caused by 
GlobalTypeTableBuilder::insertRecordAs() not inserting the record on the second
pass, thus yielding an empty ArrayRef at that record slot. Later on, upon PDB 
emission, TpiStreamBuilder::commit() would skip that empty record, thus 
offseting all indices that came after in the stream. 

This solution comes in two steps: 

1. Fix the hash calculation, by doing a multiple-step resolution, iff there are
forward references in the input stream.
2. Fix merge by resolving with multiple passes, therefore moving records with
forward references at the end of the stream. 

This patch also adds support for llvm-readoj --codeview-ghash.
Finally, fix dumpCodeViewMergedTypes() which previously could reference deleted
memory. 

Fixes PR40221 

Differential Revision: https://reviews.llvm.org/D57790 

llvm-svn: 353412

2 files changed, 11 insertions, 2 deletions

diff --git a/llvm/lib/DebugInfo/CodeView/TypeHashing.cpp b/llvm/lib/DebugInfo/CodeView/TypeHashing.cpp
index 612399ddbff..2dbc11a84f0 100644
--- a/llvm/lib/DebugInfo/CodeView/TypeHashing.cpp
+++ b/llvm/lib/DebugInfo/CodeView/TypeHashing.cpp
@@ -54,10 +54,16 @@ GloballyHashedType::hashType(ArrayRef<uint8_t> RecordData,
         reinterpret_cast<const TypeIndex *>(RefData.data()), Ref.Count);
     for (TypeIndex TI : Indices) {
       ArrayRef<uint8_t> BytesToHash;
-      if (TI.isSimple() || TI.isNoneType() || TI.toArrayIndex() >= Prev.size()) {
+      if (TI.isSimple() || TI.isNoneType()) {
         const uint8_t *IndexBytes = reinterpret_cast<const uint8_t *>(&TI);
         BytesToHash = makeArrayRef(IndexBytes, sizeof(TypeIndex));
       } else {
+        if (TI.toArrayIndex() >= Prev.size() ||
+            Prev[TI.toArrayIndex()].empty()) {
+          // There are references to yet-unhashed records. Suspend hashing for
+          // this record until all the other records are processed.
+          return {};
+        }
         BytesToHash = Prev[TI.toArrayIndex()].Hash;
       }
       S.update(BytesToHash);
diff --git a/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp b/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp
index f2a5dcb93d6..6b308453c2d 100644
--- a/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/TpiStreamBuilder.cpp
@@ -152,9 +152,12 @@ Error TpiStreamBuilder::commit(const msf::MSFLayout &Layout,
   if (auto EC = Writer.writeObject(*Header))
     return EC;
 
-  for (auto Rec : TypeRecords)
+  for (auto Rec : TypeRecords) {
+    assert(!Rec.empty()); // An empty record will not write anything, but it
+                          // would shift all offsets from here on.
     if (auto EC = Writer.writeBytes(Rec))
       return EC;
+  }
 
   if (HashStreamIndex != kInvalidStreamIndex) {
     auto HVS = WritableMappedBlockStream::createIndexedStream(