[wasm-reduce] Reduce struct.new arguments away when possible (#7118)HEADmain

If all the fields of a struct.new are defaultable, see if replacing it with a
struct.new_default preserves the behavior, and reduce that way if so.

Also add a missing --closed-world to the --remove-unused-types
invocation. Without that, it was erroring and not working, which I
noticed when testing this. The test also checks that.

1 files changed, 20 insertions, 1 deletions

diff --git a/src/tools/wasm-reduce.cpp b/src/tools/wasm-reduce.cpp
index 3b9229462..6613c8899 100644
--- a/src/tools/wasm-reduce.cpp
+++ b/src/tools/wasm-reduce.cpp
@@ -304,7 +304,7 @@ struct Reducer
       "--simplify-globals",
       "--simplify-locals --vacuum",
       "--strip",
-      "--remove-unused-types",
+      "--remove-unused-types --closed-world",
       "--vacuum"};
     auto oldSize = file_size(working);
     bool more = true;
@@ -627,6 +627,25 @@ struct Reducer
         // children (which would recreate the current state).
         return;
       }
+    } else if (auto* structNew = curr->dynCast<StructNew>()) {
+      // If all the fields are defaultable, try to replace this with a
+      // struct.new_with_default.
+      if (!structNew->isWithDefault() && structNew->type != Type::unreachable) {
+        auto& fields = structNew->type.getHeapType().getStruct().fields;
+        if (std::all_of(fields.begin(), fields.end(), [&](auto& field) {
+              return field.type.isDefaultable();
+            })) {
+          ExpressionList operands(getModule()->allocator);
+          operands.swap(structNew->operands);
+          assert(structNew->isWithDefault());
+          if (tryToReplaceCurrent(structNew)) {
+            return;
+          } else {
+            structNew->operands.swap(operands);
+            assert(!structNew->isWithDefault());
+          }
+        }
+      }
     }
     // Finally, try to replace with a child.
     for (auto* child : ChildIterator(curr)) {