[Wasm GC] Fix CoalesceLocals i31 local.get removal (#5619)

When removing a local.get we must replace it with something of the
identical type, and not make it non-nullable.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/wasm-builder.h b/src/wasm-builder.h
index 8b34d6933..73803e37d 100644
--- a/src/wasm-builder.h
+++ b/src/wasm-builder.h
@@ -1295,7 +1295,12 @@ public:
       return ExpressionManipulator::refNull(curr, curr->type);
     }
     if (curr->type.isRef() && curr->type.getHeapType() == HeapType::i31) {
-      return makeI31New(makeConst(0));
+      Expression* ret = makeI31New(makeConst(0));
+      if (curr->type.isNullable()) {
+        // To keep the type identical, wrap it in a block that adds nullability.
+        ret = makeBlock({ret}, curr->type);
+      }
+      return ret;
     }
     if (!curr->type.isBasic()) {
       // We can't do any better, keep the original.