[Assignment Tracking][9/*] Don't drop DIAssignID in dropUnknownNonDebugMetadata

The Assignment Tracking debug-info feature is outlined in this RFC:

https://discourse.llvm.org/t/
rfc-assignment-tracking-a-better-way-of-specifying-variable-locations-in-ir

A DIAssignID attachment is debug metadata, so don't drop it.

Reviewed By: jmorse

Differential Revision: https://reviews.llvm.org/D133292

1 files changed, 3 insertions, 6 deletions

diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index 533690203189..bde83717ebef 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/llvm/lib/IR/Metadata.cpp
@@ -1403,15 +1403,12 @@ void Instruction::dropUnknownNonDebugMetadata(ArrayRef<unsigned> KnownIDs) {
   if (!Value::hasMetadata())
     return; // Nothing to remove!
 
-  if (KnownIDs.empty()) {
-    // Just drop our entry at the store.
-    clearMetadata();
-    return;
-  }
-
   SmallSet<unsigned, 4> KnownSet;
   KnownSet.insert(KnownIDs.begin(), KnownIDs.end());
 
+  // A DIAssignID attachment is debug metadata, don't drop it.
+  KnownSet.insert(LLVMContext::MD_DIAssignID);
+
   auto &MetadataStore = getContext().pImpl->ValueMetadata;
   auto &Info = MetadataStore[this];
   assert(!Info.empty() && "bit out of sync with hash table");