[threads] Simplify and generalize heap type writing without GC

scripts/fuzz_opt.py

@@ -361,6 +361,7 @@ def is_git_repo():
     'shared-absheaptype.wast',
     'type-ssa-shared.wast',
     'shared-ref_eq.wast',
+    'shared-null-no-gc.wast',
 ]
 
 

src/wasm/wasm-binary.cpp

@@ -1629,20 +1629,7 @@ void WasmBinaryWriter::writeHeapType(HeapType type) {
   // only actually valid with GC. Otherwise, emit the corresponding valid top
   // types instead.
   if (!wasm->features.hasGC()) {
-    if (HeapType::isSubType(type, HeapType::func)) {
-      type = HeapType::func;
-    } else if (HeapType::isSubType(type, HeapType::ext)) {
-      type = HeapType::ext;
-    } else if (HeapType::isSubType(type, HeapType::exn)) {
-      type = HeapType::exn;
-    } else if (wasm->features.hasStrings()) {
-      // Strings are enabled, and this isn't a func or an ext, so it must be a
-      // string type (string or stringview), which we'll emit below, or a bottom
-      // type (which we must allow, because we wouldn't know whether to emit a
-      // string or stringview for it).
-    } else {
-      WASM_UNREACHABLE("invalid type without GC");
-    }
+    type = type.getTop();
   }
 
   if (!type.isBasic()) {

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

@@ -0,0 +1,19 @@
+;; 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.
+
+;; RUN: wasm-opt %s --enable-reference-types --enable-shared-everything --roundtrip -S -o - | filecheck %s
+
+(module
+ ;; CHECK:      (func $test
+ ;; CHECK-NEXT:  (drop
+ ;; CHECK-NEXT:   (ref.null (shared nofunc))
+ ;; CHECK-NEXT:  )
+ ;; CHECK-NEXT: )
+ (func $test
+  (drop
+   (ref.null (shared func))
+  )
+ )
+)