Fuzzer: Add support for creating structs and arrays in makeConst (#4707)

#4659 adds a testcase with an import of (ref $struct). This could cause an error in
the fuzzer, since it wants to remove imports (because the various fuzzers cannot pass
in custom imports - they want to just run the wasm). When it tries to remove that
import it tries to create a constant for a struct reference, and fails. To fix that, add
enough support to create structs and arrays at least in the simple case where all their
fields are defaultable.

1 files changed, 20 insertions, 8 deletions

diff --git a/src/tools/fuzzing/fuzzing.cpp b/src/tools/fuzzing/fuzzing.cpp
index fe091c91f..e5afbf559 100644
--- a/src/tools/fuzzing/fuzzing.cpp
+++ b/src/tools/fuzzing/fuzzing.cpp
@@ -2017,23 +2017,35 @@ Expression* TranslateToFuzzReader::makeConstCompoundRef(Type type) {
   assert(wasm.features.hasReferenceTypes());
   if (heapType.isSignature()) {
     return makeRefFuncConst(type);
-  } else {
-    // TODO: Handle nontrivial array and struct types.
   }
+
   // We weren't able to directly materialize a non-null constant. Try again to
   // create a null.
   if (type.isNullable()) {
     return builder.makeRefNull(type);
   }
+
   // We have to produce a non-null value. Possibly create a null and cast it
   // to non-null even though that will trap at runtime. We must have a
-  // function context because the cast is not allowed in globals.
-  if (!funcContext) {
-    std::cerr << type << "\n";
+  // function context for this because the cast is not allowed in globals.
+  if (funcContext) {
+    return builder.makeRefAs(RefAsNonNull,
+                             builder.makeRefNull(Type(heapType, Nullable)));
+  }
+
+  // Otherwise, we are not in a function context. This can happen if we need
+  // 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*>{});
+  } else if (type.isArray()) {
+    return builder.makeArrayNew(type.getHeapType(), makeConst(Type::i32));
+  } else {
+    WASM_UNREACHABLE("bad user-defined ref type");
   }
-  assert(funcContext);
-  return builder.makeRefAs(RefAsNonNull,
-                           builder.makeRefNull(Type(heapType, Nullable)));
 }
 
 Expression* TranslateToFuzzReader::buildUnary(const UnaryArgs& args) {