[threads] Simplify and generalize reftype writing without GC (#6766)

Similar to #6765, but for types instead of heap types. Generalize the
logic for transforming written reference types to types that are
supported without GC so that it will automatically handle shared types
and other new types correctly.

scripts/fuzz_opt.py

@@ -361,7 +361,7 @@ def is_git_repo():
     'shared-absheaptype.wast',
     'type-ssa-shared.wast',
     'shared-ref_eq.wast',
-    'shared-null-no-gc.wast',
+    'shared-types-no-gc.wast',
 ]
 
 

src/wasm/wasm-binary.cpp

@@ -1520,23 +1520,15 @@ void WasmBinaryWriter::writeType(Type type) {
     // internally use more refined versions of those types, but we cannot emit
     // those more refined types.
     if (!wasm->features.hasGC()) {
-      if (Type::isSubType(type, Type(HeapType::func, Nullable))) {
-        o << S32LEB(BinaryConsts::EncodedType::funcref);
-        return;
-      }
-      if (Type::isSubType(type, Type(HeapType::ext, Nullable))) {
-        o << S32LEB(BinaryConsts::EncodedType::externref);
-        return;
-      }
-      if (Type::isSubType(type, Type(HeapType::exn, Nullable))) {
-        o << S32LEB(BinaryConsts::EncodedType::exnref);
-        return;
-      }
-      if (Type::isSubType(type, Type(HeapType::string, Nullable))) {
-        o << S32LEB(BinaryConsts::EncodedType::stringref);
-        return;
+      auto ht = type.getHeapType();
+      if (ht.isBasic() && ht.getBasic(Unshared) == HeapType::string) {
+        // Do not overgeneralize stringref to anyref. We have tests that when a
+        // stringref is expected, we actually get a stringref. If we see a
+        // string, the stringref feature must be enabled.
+        type = Type(HeapTypes::string.getBasic(ht.getShared()), Nullable);
+      } else {
+        type = Type(type.getHeapType().getTop(), Nullable);
       }
-      WASM_UNREACHABLE("bad type without GC");
     }
     auto heapType = type.getHeapType();
     if (type.isNullable() && heapType.isBasic() && !heapType.isShared()) {

test/lit/basic/shared-null-no-gc.wast → test/lit/basic/shared-types-no-gc.wast

@@ -1,19 +1,26 @@
 ;; NOTE: Assertions have been generated by update_lit_checks.py and should not be edited.
 
-;; Test that we can write a binary without crashing when using a shared bottom
-;; type without GC enabled.
+;; Test that we can write a binary without crashing when using shared reference
+;; types without GC enabled.
 
 ;; RUN: wasm-opt %s --enable-reference-types --enable-shared-everything --roundtrip -S -o - | filecheck %s
 
 (module
- ;; CHECK:      (func $test
+ ;; CHECK:      (func $null
  ;; CHECK-NEXT:  (drop
  ;; CHECK-NEXT:   (ref.null (shared nofunc))
  ;; CHECK-NEXT:  )
  ;; CHECK-NEXT: )
- (func $test
+ (func $null
   (drop
    (ref.null (shared func))
   )
  )
+
+ ;; CHECK:      (func $signature (result (ref null (shared func)))
+ ;; CHECK-NEXT:  (unreachable)
+ ;; CHECK-NEXT: )
+ (func $signature (result (ref null (shared func)))
+  (unreachable)
+ )
 )