[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, 33 insertions, 1 deletions

diff --git a/src/wasm/wasm-validator.cpp b/src/wasm/wasm-validator.cpp
index c6e22899c..e97541444 100644
--- a/src/wasm/wasm-validator.cpp
+++ b/src/wasm/wasm-validator.cpp
@@ -2238,7 +2238,39 @@ void FunctionValidator::visitStructNew(StructNew* curr) {
   shouldBeTrue(getModule()->features.hasGC(),
                curr,
                "struct.new requires gc to be enabled");
-  WASM_UNREACHABLE("TODO (gc): struct.new");
+  if (curr->type == Type::unreachable) {
+    return;
+  }
+  if (!shouldBeTrue(
+        curr->rtt->type.isRtt(), curr, "struct.new rtt must be rtt")) {
+    return;
+  }
+  auto heapType = curr->rtt->type.getHeapType();
+  if (!shouldBeTrue(
+        heapType.isStruct(), curr, "struct.new heap type must be struct")) {
+    return;
+  }
+  const auto& fields = heapType.getStruct().fields;
+  if (curr->isWithDefault()) {
+    shouldBeTrue(curr->operands.empty(),
+                 curr,
+                 "struct.new_with_default should have no operands");
+    // All the fields must be defaultable.
+    for (const auto& field : fields) {
+      // TODO: add type.isDefaultable()?
+      shouldBeTrue(!field.type.isRef() || field.type.isNullable(),
+                   field,
+                   "struct.new_with_default value type must be defaultable");
+    }
+  } else {
+    // All the fields must have the proper type.
+    for (Index i = 0; i < fields.size(); i++) {
+      shouldBeSubType(curr->operands[i]->type,
+                      fields[i].type,
+                      curr,
+                      "struct.new operand must have proper type");
+    }
+  }
 }
 
 void FunctionValidator::visitStructGet(StructGet* curr) {