Add a TypeBuilder API for copying a heap type (#6828)

Given a function that maps the old child heap types to new child heap
types, the new API takes care of copying the rest of the structure of a
given heap type into a TypeBuilder slot.

Use the new API in GlobalTypeRewriter::rebuildTypes. It will also be
used in an upcoming type optimization. This refactoring also required
adding the ability to clear the supertype of a TypeBuilder slot, which
was previously not possible.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/wasm/wasm-type.cpp b/src/wasm/wasm-type.cpp
index 173e4b8c3..011c51e7b 100644
--- a/src/wasm/wasm-type.cpp
+++ b/src/wasm/wasm-type.cpp
@@ -2532,10 +2532,10 @@ Type TypeBuilder::getTempRefType(HeapType type, Nullability nullable) {
   return markTemp(impl->typeStore.insert(TypeInfo(type, nullable)));
 }
 
-void TypeBuilder::setSubType(size_t i, HeapType super) {
+void TypeBuilder::setSubType(size_t i, std::optional<HeapType> super) {
   assert(i < size() && "index out of bounds");
   HeapTypeInfo* sub = impl->entries[i].info.get();
-  sub->supertype = getHeapTypeInfo(super);
+  sub->supertype = super ? getHeapTypeInfo(*super) : nullptr;
 }
 
 void TypeBuilder::createRecGroup(size_t index, size_t length) {