8336095: Use-after-free in Superword leads to memory corruption

Reviewed-by: epeter, kvn, rrich

src/hotspot/share/opto/loopnode.hpp

@@ -611,6 +611,7 @@ public:
       _head(head), _tail(tail),
       _phase(phase),
       _local_loop_unroll_limit(0), _local_loop_unroll_factor(0),
+      _body(Compile::current()->comp_arena()),
       _nest(0), _irreducible(0), _has_call(0), _has_sfpt(0), _rce_candidate(0),
       _has_range_checks(0), _has_range_checks_computed(0),
       _safepts(nullptr),