is_function/3 opcode doesn't handle arity as a term

[jakub-gonet]

I will try to find minimal repro (or stacktraces/opcodes sequence) in few days but when working on porting Erlang to WASM I noticed that OP_IS_FUNCTION2 sometimes crashed.

After decoding it as a term, the crash disappeared:

@ -5252,37 +5251,41 @@ wait_timeout_trap_handler:
                   DECODE_LABEL(label, pc)
                   term arg1;
                   DECODE_COMPACT_TERM(arg1, pc)
-                  unsigned int arity;
-                  DECODE_INTEGER(arity, pc)
+                  term arity_term;
+                  DECODE_COMPACT_TERM(arity_term, pc)

                   #ifdef IMPL_EXECUTE_LOOP
-                      if (term_is_function(arg1)) {
-                          const term *boxed_value = term_to_const_term_ptr(arg1);
+                      if (term_is_function(arg1)) {
+                          const uint32_t arity = term_to_int(arity_term);
+                          const term *boxed_value = term_to_const_term_ptr(arg1);

Not sure if AVM does some post-processing for BEAM bytecode when compiling to .avm or something else is in play.

BEAM book suggests that the opcode should have term/register (depending on %hot/%cold modifiers) type in emulator mode but literal in JIT