[GC] Add struct.new and start to test interesting execution (#3433)

With struct.new read/write support, we can start to do interesting
things! This adds a test of creating a struct and seeing that references
behave like references, that is, if we write to the value X refers to, and
if Y refers to the same thing, when reading from Y's value we see the
change as well.

The test is run through all of -O1, which uncovered a minor issue in
Precompute: We can't try to precompute a reference type, as we can't
replace a reference with a value.

Note btw that the test shows the optimizer properly running
CoalesceLocals on reference types, merging two locals.

1 files changed, 20 insertions, 1 deletions

diff --git a/src/wasm-interpreter.h b/src/wasm-interpreter.h
index 65a4417c8..bf02b7987 100644
--- a/src/wasm-interpreter.h
+++ b/src/wasm-interpreter.h
@@ -1398,7 +1398,26 @@ public:
   }
   Flow visitStructNew(StructNew* curr) {
     NOTE_ENTER("StructNew");
-    WASM_UNREACHABLE("TODO (gc): struct.new");
+    auto rtt = this->visit(curr->rtt);
+    if (rtt.breaking()) {
+      return rtt;
+    }
+    const auto& fields = curr->rtt->type.getHeapType().getStruct().fields;
+    Literals data;
+    data.resize(fields.size());
+    for (Index i = 0; i < fields.size(); i++) {
+      if (curr->isWithDefault()) {
+        data[i] = Literal::makeZero(fields[i].type);
+      } else {
+        auto value = this->visit(curr->operands[i]);
+        if (value.breaking()) {
+          return value;
+        }
+        data[i] = value.getSingleValue();
+      }
+    }
+    return Flow(
+      Literal(std::shared_ptr<Literals>(new Literals(data)), curr->type));
   }
   Flow visitStructGet(StructGet* curr) {
     NOTE_ENTER("StructGet");