[Wasm GC] Fix the intersection of a bottom type null (#5128)

When the heap types are not subtypes of each other, but a null is possible, the
intersection exists and is a null. That null must be the shared bottom type.

1 files changed, 8 insertions, 2 deletions

diff --git a/src/ir/possible-contents.cpp b/src/ir/possible-contents.cpp
index 8349939e1..cd8bd1516 100644
--- a/src/ir/possible-contents.cpp
+++ b/src/ir/possible-contents.cpp
@@ -195,11 +195,17 @@ void PossibleContents::intersectWithFullCone(const PossibleContents& other) {
   }
 
   // If the heap types are not compatible then they are in separate hierarchies
-  // and there is no intersection.
+  // and there is no intersection, aside from possibly a null of the bottom
+  // type.
   auto isSubType = HeapType::isSubType(heapType, otherHeapType);
   auto otherIsSubType = HeapType::isSubType(otherHeapType, heapType);
   if (!isSubType && !otherIsSubType) {
-    value = None();
+    if (nullability == Nullable &&
+        heapType.getBottom() == otherHeapType.getBottom()) {
+      value = Literal::makeNull(heapType.getBottom());
+    } else {
+      value = None();
+    }
     return;
   }