[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, 12 insertions, 2 deletions

diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index 2edd069d9..5c2acf3f0 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -1702,7 +1702,12 @@ struct PrintExpressionContents
     printHeapTypeName(o, curr->type.getRtt().heapType);
   }
   void visitStructNew(StructNew* curr) {
-    WASM_UNREACHABLE("TODO (gc): struct.new");
+    printMedium(o, "struct.new_");
+    if (curr->isWithDefault()) {
+      o << "default_";
+    }
+    o << "with_rtt ";
+    printHeapTypeName(o, curr->rtt->type.getRtt().heapType);
   }
   void visitStructGet(StructGet* curr) {
     const auto& field =
@@ -2391,7 +2396,12 @@ struct PrintSExpression : public OverriddenVisitor<PrintSExpression> {
   void visitStructNew(StructNew* curr) {
     o << '(';
     PrintExpressionContents(currFunction, o).visit(curr);
-    WASM_UNREACHABLE("TODO (gc): struct.new");
+    incIndent();
+    printFullLine(curr->rtt);
+    for (auto& operand : curr->operands) {
+      printFullLine(operand);
+    }
+    decIndent();
   }
   void visitStructGet(StructGet* curr) {
     o << '(';