[Wasm GC] i31get can trap (#4825)

2 files changed, 27 insertions, 1 deletions

diff --git a/src/ir/effects.h b/src/ir/effects.h
index 43d4868d8..e3f4b565d 100644
--- a/src/ir/effects.h
+++ b/src/ir/effects.h
@@ -653,7 +653,12 @@ private:
     void visitTupleMake(TupleMake* curr) {}
     void visitTupleExtract(TupleExtract* curr) {}
     void visitI31New(I31New* curr) {}
-    void visitI31Get(I31Get* curr) {}
+    void visitI31Get(I31Get* curr) {
+      // traps when the ref is null
+      if (curr->i31->type.isNullable()) {
+        parent.implicitTrap = true;
+      }
+    }
     void visitCallRef(CallRef* curr) {
       parent.calls = true;
       if (parent.features.hasExceptionHandling() && parent.tryDepth == 0) {
diff --git a/test/lit/passes/vacuum-gc.wast b/test/lit/passes/vacuum-gc.wast
index f37085406..71f0e39c2 100644
--- a/test/lit/passes/vacuum-gc.wast
+++ b/test/lit/passes/vacuum-gc.wast
@@ -75,4 +75,25 @@
       )
     )
   )
+
+  ;; CHECK:      (func $drop-i31.get (param $ref (ref null i31)) (param $ref-nn i31ref)
+  ;; CHECK-NEXT:  (drop
+  ;; CHECK-NEXT:   (i31.get_s
+  ;; CHECK-NEXT:    (local.get $ref)
+  ;; CHECK-NEXT:   )
+  ;; CHECK-NEXT:  )
+  ;; CHECK-NEXT: )
+  (func $drop-i31.get (param $ref (ref null i31)) (param $ref-nn (ref i31))
+    ;; A nullable get might trap, so only the second item can be removed.
+    (drop
+      (i31.get_s
+        (local.get $ref)
+      )
+    )
+    (drop
+      (i31.get_s
+        (local.get $ref-nn)
+      )
+    )
+  )
 )