[Wasm GC] rtt.fresh_sub (#3936)

This is the same as rtt.sub, but creates a "new" rtt each time. See

https://docs.google.com/document/d/1DklC3qVuOdLHSXB5UXghM_syCh-4cMinQ50ICiXnK3Q/edit#

The old Literal implementation of rtts becomes a little more complex here,
as it was designed for the original spec where only structure matters. It may
be worth a complete redesign there, but for now as the spec is in flux I think
the approach here is good enough.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/wasm/wasm-binary.cpp b/src/wasm/wasm-binary.cpp
index a4df4ed16..7625d1f2a 100644
--- a/src/wasm/wasm-binary.cpp
+++ b/src/wasm/wasm-binary.cpp
@@ -6419,12 +6419,16 @@ bool WasmBinaryBuilder::maybeVisitRttCanon(Expression*& out, uint32_t code) {
 }
 
 bool WasmBinaryBuilder::maybeVisitRttSub(Expression*& out, uint32_t code) {
-  if (code != BinaryConsts::RttSub) {
+  if (code != BinaryConsts::RttSub && code != BinaryConsts::RttFreshSub) {
     return false;
   }
   auto targetHeapType = getIndexedHeapType();
   auto* parent = popNonVoidExpression();
-  out = Builder(wasm).makeRttSub(targetHeapType, parent);
+  if (code == BinaryConsts::RttSub) {
+    out = Builder(wasm).makeRttSub(targetHeapType, parent);
+  } else {
+    out = Builder(wasm).makeRttFreshSub(targetHeapType, parent);
+  }
   return true;
 }