[threads] Allow i31refs of mixed shareability to compare equal (#6752)

Normally, values of different types can never compare equal to each
other, but since i31refs are not actually allocations, `ref.eq` has no
way to differentiate a shared i31ref and an unshared i31ref with the
same value, so it will report them as equal. Update the implementation
of value equality to reflect this correctly.

Author: tlively

src/wasm/literal.cpp

@@ -412,6 +412,14 @@ void Literal::getBits(uint8_t (&buf)[16]) const {
 }
 
 bool Literal::operator==(const Literal& other) const {
+  // As a special case, shared and unshared i31 can compare equal even if their
+  // types are different (because one is shared and the other is not).
+  if (type.isRef() && other.type.isRef() && type.getHeapType().isBasic() &&
+      other.type.getHeapType().isBasic() &&
+      type.getHeapType().getBasic(Unshared) == HeapType::i31 &&
+      other.type.getHeapType().getBasic(Unshared) == HeapType::i31) {
+    return i32 == other.i32;
+  }
   if (type != other.type) {
     return false;
   }
@@ -445,9 +453,7 @@ bool Literal::operator==(const Literal& other) const {
     if (type.isData()) {
       return gcData == other.gcData;
     }
-    if (type.getHeapType() == HeapType::i31) {
-      return i32 == other.i32;
-    }
+    // i31 already handled.
     WASM_UNREACHABLE("unexpected type");
   }
   WASM_UNREACHABLE("unexpected type");

test/spec/shared-polymorphism.wast

@@ -23,3 +23,14 @@
     (extern.convert_any (local.get 0))
   )
 )
+
+(module
+  (func (export "eq") (param i32 i32) (result i32)
+    (ref.eq (ref.i31 (local.get 0)) (ref.i31_shared (local.get 1)))
+  )
+)
+
+(assert_return (invoke "eq" (i32.const 0) (i32.const 0)) (i32.const 1))
+(assert_return (invoke "eq" (i32.const 0) (i32.const 1)) (i32.const 0))
+(assert_return (invoke "eq" (i32.const 1) (i32.const 0)) (i32.const 0))
+(assert_return (invoke "eq" (i32.const 1) (i32.const 1)) (i32.const 1))