Fuzzer: Create struct/array initial values when fields are nondefaultable (#5529)

1 files changed, 18 insertions, 4 deletions

diff --git a/src/tools/fuzzing/fuzzing.cpp b/src/tools/fuzzing/fuzzing.cpp
index c4c47ee23..03ee7d376 100644
--- a/src/tools/fuzzing/fuzzing.cpp
+++ b/src/tools/fuzzing/fuzzing.cpp
@@ -2146,12 +2146,26 @@ Expression* TranslateToFuzzReader::makeConstCompoundRef(Type type) {
   // to make a constant for the initializer of a global, for example. We've
   // already handled simple cases of this above, for basic heap types, so what
   // we have left here are user-defined heap types like structs.
-  // TODO: support non-defaultable fields. for now, just use default values.
   if (type.isStruct()) {
-    return builder.makeStructNew(type.getHeapType(),
-                                 std::vector<Expression*>{});
+    auto& fields = heapType.getStruct().fields;
+    std::vector<Expression*> values;
+    // TODO: use non-default values randomly even when not necessary, sometimes
+    if (std::any_of(fields.begin(), fields.end(), [&](const Field& field) {
+          return !field.type.isDefaultable();
+        })) {
+      // There is a nondefaultable field, which we must create.
+      for (auto& field : fields) {
+        values.push_back(makeTrivial(field.type));
+      }
+    }
+    return builder.makeStructNew(heapType, values);
   } else if (type.isArray()) {
-    return builder.makeArrayNew(type.getHeapType(), makeConst(Type::i32));
+    auto element = heapType.getArray().element;
+    Expression* init = nullptr;
+    if (!element.type.isDefaultable()) {
+      init = makeTrivial(element.type);
+    }
+    return builder.makeArrayNew(type.getHeapType(), makeConst(Type::i32), init);
   } else {
     WASM_UNREACHABLE("bad user-defined ref type");
   }