[DebugInfo][Metadata] Make AllEnumTypes holding TrackingMDNodeRef

Having AllEnumtypes to be a vector of TrackingMDNodeRef makes it possible
to reflect changes in metadata in the vector if they took place before DIBuilder
being finalized.

Otherwise, we end up with heap-use-after-free because AllEnumTypes contains
metadata that no longer valid.

Consider a case where we have a class containing a definition of a enum,
so this enum has the class as a scope. For some reason (doesn't matter for
the current issue), we create a temporary debug metadata for this class, and
then resolve it while finalizing CGDebugInfo.

In the case of collision during uniqifying the temporary, we then need
to replace its uses with a new pointer. If a temporary's user is unique
(this is the enum mentioned above), we may need re-uniquefying it,
which may return a new pointer in the case of another collision.
If so, the pointer we stored in AllEnumTypes vector become dangling.
Making AllEnumTypes hodling TrackingMDNodeRef should solve this problem
(see debug-info-enum-metadata-collision.cpp test for details).

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D137067

1 files changed, 4 insertions, 2 deletions

diff --git a/llvm/lib/IR/DIBuilder.cpp b/llvm/lib/IR/DIBuilder.cpp
index fada07a..76d7ade 100644
--- a/llvm/lib/IR/DIBuilder.cpp
+++ b/llvm/lib/IR/DIBuilder.cpp
@@ -84,7 +84,9 @@ void DIBuilder::finalize() {
   }
 
   if (!AllEnumTypes.empty())
-    CUNode->replaceEnumTypes(MDTuple::get(VMContext, AllEnumTypes));
+    CUNode->replaceEnumTypes(MDTuple::get(
+        VMContext, SmallVector<Metadata *, 16>(AllEnumTypes.begin(),
+                                               AllEnumTypes.end())));
 
   SmallVector<Metadata *, 16> RetainValues;
   // Declarations and definitions of the same type may be retained. Some
@@ -556,7 +558,7 @@ DICompositeType *DIBuilder::createEnumerationType(
       getNonCompileUnitScope(Scope), UnderlyingType, SizeInBits, AlignInBits, 0,
       IsScoped ? DINode::FlagEnumClass : DINode::FlagZero, Elements, 0, nullptr,
       nullptr, UniqueIdentifier);
-  AllEnumTypes.push_back(CTy);
+  AllEnumTypes.emplace_back(CTy);
   trackIfUnresolved(CTy);
   return CTy;
 }