[NFC] Simplify rec group initialization in wasm-type.cpp (#5683)

Now that we no longer support constructing basic heap types in TypeBuilder, we
can fully initialize rec groups when they are created, rather than having to
initialize them later during the build step after any basic types have been
canonicalized. Alongside that change, also simplify the process of initializing
a type builder slot to avoid completely overwriting the HeapTypeInfo in the slot
and avoid the hacky workarounds that required.

src/wasm-type.h

@@ -540,6 +540,7 @@ struct Struct {
 
   // Prevent accidental copies
   Struct& operator=(const Struct&) = delete;
+  Struct& operator=(Struct&&) = default;
 };
 
 struct Array {
@@ -550,6 +551,8 @@ struct Array {
   bool operator==(const Array& other) const { return element == other.element; }
   bool operator!=(const Array& other) const { return !(*this == other); }
   std::string toString() const;
+
+  Array& operator=(const Array& other) = default;
 };
 
 // TypeBuilder - allows for the construction of recursive types. Contains a

src/wasm/wasm-type.cpp

@@ -102,7 +102,6 @@ struct HeapTypeInfo {
     ArrayKind,
   } kind;
   union {
-    HeapType::BasicHeapType basic;
     Signature signature;
     Struct struct_;
     Array array;
@@ -121,7 +120,6 @@ struct HeapTypeInfo {
   constexpr bool isArray() const { return kind == ArrayKind; }
   constexpr bool isData() const { return isStruct() || isArray(); }
 
-  HeapTypeInfo& operator=(const HeapTypeInfo& other);
   bool operator==(const HeapTypeInfo& other) const;
   bool operator!=(const HeapTypeInfo& other) const { return !(*this == other); }
 };
@@ -563,9 +561,11 @@ bool TypeInfo::operator==(const TypeInfo& other) const {
 }
 
 HeapTypeInfo::HeapTypeInfo(const HeapTypeInfo& other) {
-  kind = other.kind;
+  isTemp = other.isTemp;
   supertype = other.supertype;
   recGroup = other.recGroup;
+  recGroupIndex = other.recGroupIndex;
+  kind = other.kind;
   switch (kind) {
     case SignatureKind:
       new (&signature) auto(other.signature);
@@ -595,14 +595,6 @@ HeapTypeInfo::~HeapTypeInfo() {
   WASM_UNREACHABLE("unexpected kind");
 }
 
-HeapTypeInfo& HeapTypeInfo::operator=(const HeapTypeInfo& other) {
-  if (&other != this) {
-    this->~HeapTypeInfo();
-    new (this) HeapTypeInfo(other);
-  }
-  return *this;
-}
-
 bool HeapTypeInfo::operator==(const HeapTypeInfo& other) const {
   return this == &other;
 }
@@ -2247,14 +2239,21 @@ struct TypeBuilder::Impl {
       // to refer to it before it is initialized. Arbitrarily choose a default
       // value.
       info = std::make_unique<HeapTypeInfo>(Signature());
-      set(Signature());
-      initialized = false;
+      info->isTemp = true;
     }
     void set(HeapTypeInfo&& hti) {
-      hti.supertype = info->supertype;
-      hti.recGroup = info->recGroup;
-      *info = std::move(hti);
-      info->isTemp = true;
+      info->kind = hti.kind;
+      switch (info->kind) {
+        case HeapTypeInfo::SignatureKind:
+          info->signature = hti.signature;
+          break;
+        case HeapTypeInfo::StructKind:
+          info->struct_ = std::move(hti.struct_);
+          break;
+        case HeapTypeInfo::ArrayKind:
+          info->array = hti.array;
+          break;
+      }
       initialized = true;
     }
     HeapType get() { return HeapType(TypeID(info.get())); }
@@ -2326,18 +2325,22 @@ void TypeBuilder::setSubType(size_t i, HeapType super) {
   sub->supertype = getHeapTypeInfo(super);
 }
 
-void TypeBuilder::createRecGroup(size_t i, size_t length) {
-  assert(i <= size() && i + length <= size() && "group out of bounds");
+void TypeBuilder::createRecGroup(size_t index, size_t length) {
+  assert(index <= size() && index + length <= size() && "group out of bounds");
   // Only materialize nontrivial recursion groups.
   if (length < 2) {
     return;
   }
   auto& groups = impl->recGroups;
   groups.emplace_back(std::make_unique<RecGroupInfo>());
-  for (; length > 0; --length) {
-    auto& info = impl->entries[i + length - 1].info;
+  groups.back()->reserve(length);
+  for (size_t i = 0; i < length; ++i) {
+    auto& info = impl->entries[index + i].info;
     assert(info->recGroup == nullptr && "group already assigned");
-    info->recGroup = groups.back().get();
+    auto* recGroup = groups.back().get();
+    recGroup->push_back(asHeapType(info));
+    info->recGroup = recGroup;
+    info->recGroupIndex = i;
   }
 }
 
@@ -2592,13 +2595,6 @@ validateSubtyping(const std::vector<HeapType>& types) {
 std::optional<TypeBuilder::Error> canonicalizeIsorecursive(
   CanonicalizationState& state,
   std::vector<std::unique_ptr<RecGroupInfo>>& recGroupInfos) {
-  // Fill out the recursion groups.
-  for (auto& info : state.newInfos) {
-    if (info->recGroup != nullptr) {
-      info->recGroupIndex = info->recGroup->size();
-      info->recGroup->push_back(asHeapType(info));
-    }
-  }
 
   // Map rec groups to the unique pointers to their infos.
   std::unordered_map<RecGroup, std::unique_ptr<RecGroupInfo>> groupInfoMap;
@@ -2718,11 +2714,6 @@ TypeBuilder::BuildResult TypeBuilder::build() {
     state.newInfos.emplace_back(std::move(info));
   }
 
-#if TRACE_CANONICALIZATION
-  std::cerr << "After replacing basic heap types:\n";
-  state.dump();
-#endif
-
 #if TIME_CANONICALIZATION
   using instant_t = std::chrono::time_point<std::chrono::steady_clock>;
   auto getMillis = [&](instant_t start, instant_t end) {