[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, 9 insertions, 0 deletions

diff --git a/test/gtest/possible-contents.cpp b/test/gtest/possible-contents.cpp
index 04c288806..7b8f0c4a8 100644
--- a/test/gtest/possible-contents.cpp
+++ b/test/gtest/possible-contents.cpp
@@ -481,6 +481,8 @@ void assertIntersection(PossibleContents a,
   auto intersection = a;
   intersection.intersectWithFullCone(b);
   EXPECT_EQ(intersection, result);
+
+  EXPECT_EQ(PossibleContents::haveIntersection(a, b), !result.isNone());
 }
 
 TEST_F(PossibleContentsTest, TestStructCones) {
@@ -713,6 +715,13 @@ TEST_F(PossibleContentsTest, TestStructCones) {
   assertIntersection(nnExactA, PossibleContents::fullConeType(nullB), none);
   assertIntersection(exactA, PossibleContents::fullConeType(nnB), none);
 
+  // A and E have no intersection, so the only possibility is a null, and that
+  // null must be the bottom type.
+  assertIntersection(
+    exactA,
+    PossibleContents::fullConeType(nullE),
+    PossibleContents::literal(Literal::makeNull(HeapType::none)));
+
   assertIntersection(PossibleContents::coneType(nnA, 1),
                      PossibleContents::fullConeType(nnB),
                      nnExactB);