[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.

3 files changed, 20 insertions, 21 deletions

diff --git a/scripts/fuzz_opt.py b/scripts/fuzz_opt.py
index a591f9414..e7826c0f3 100755
--- a/scripts/fuzz_opt.py
+++ b/scripts/fuzz_opt.py
@@ -361,7 +361,7 @@ INITIAL_CONTENTS_IGNORE = [
     'shared-absheaptype.wast',
     'type-ssa-shared.wast',
     'shared-ref_eq.wast',
-    'shared-null-no-gc.wast',
+    'shared-types-no-gc.wast',
 ]
 
 
diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index d35edadc8..20815b701 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/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()) {
diff --git a/test/lit/basic/shared-null-no-gc.wast b/test/lit/basic/shared-types-no-gc.wast
index b920f80f8..94c664f58 100644
--- a/test/lit/basic/shared-null-no-gc.wast
+++ b/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)
+ )
 )