Add binary format parse checking for ref.as input type (#4389)

If that type is not valid then we cannot even create and finalize the node,
which means we'd hit an assertion inside finalize(), before we reach the
validator.

Fixes #4383

src/wasm/wasm-binary.cpp

@@ -6898,6 +6898,9 @@ void WasmBinaryBuilder::visitRefAs(RefAs* curr, uint8_t code) {
       WASM_UNREACHABLE("invalid code for ref.as_*");
   }
   curr->value = popNonVoidExpression();
+  if (!curr->value->type.isRef() && curr->value->type != Type::unreachable) {
+    throwError("bad input type for ref.as: " + curr->value->type.toString());
+  }
   curr->finalize();
 }
 

test/lit/binary/bad-ref-as.test

@@ -0,0 +1,6 @@
+;; Test that we error properly on a file with a ref.as of a non-ref type.
+
+;; RUN: not wasm-opt %s.wasm 2>&1 | filecheck %s
+
+;; CHECK: parse exception: bad input type for ref.as: i32
+