[Wasm GC] OptimizeInstructions: ref.as_non_null of null will trap (#5635)

Trivial peephole optimization. Some work was needed in the tests as some of
them relied on that pattern for convenience, so I modified them to try to keep
them testing the same thing as much as possible (for one, struct.set.null.fallthrough,
I don't think we can actually keep testing the same, as the situation should not
be possible any more).

1 files changed, 3 insertions, 0 deletions

diff --git a/src/passes/OptimizeInstructions.cpp b/src/passes/OptimizeInstructions.cpp
index 3a5f56be9..e71519012 100644
--- a/src/passes/OptimizeInstructions.cpp
+++ b/src/passes/OptimizeInstructions.cpp
@@ -2227,6 +2227,9 @@ struct OptimizeInstructions
     }
 
     assert(curr->op == RefAsNonNull);
+    if (trapOnNull(curr, curr->value)) {
+      return;
+    }
     skipNonNullCast(curr->value, curr);
     if (!curr->value->type.isNullable()) {
       replaceCurrent(curr->value);