py: Modify bytecode "with" behaviour so it doesn't use any heap.
Before this patch a "with" block needed to create a bound method object
on the heap for the __exit__ call. Now it doesn't because we use
load_method instead of load_attr, and save the method+self on the stack.
diff --git a/py/vm.c b/py/vm.c
index 55203b0..1af3636 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -548,68 +548,82 @@
ENTRY(MP_BC_SETUP_WITH): {
MARK_EXC_IP_SELECTIVE();
+ // stack: (..., ctx_mgr)
mp_obj_t obj = TOP();
- SET_TOP(mp_load_attr(obj, MP_QSTR___exit__));
- mp_load_method(obj, MP_QSTR___enter__, sp + 1);
- mp_obj_t ret = mp_call_method_n_kw(0, 0, sp + 1);
+ mp_load_method(obj, MP_QSTR___exit__, sp);
+ mp_load_method(obj, MP_QSTR___enter__, sp + 2);
+ mp_obj_t ret = mp_call_method_n_kw(0, 0, sp + 2);
+ sp += 1;
PUSH_EXC_BLOCK(1);
PUSH(ret);
+ // stack: (..., __exit__, ctx_mgr, as_value)
DISPATCH();
}
ENTRY(MP_BC_WITH_CLEANUP): {
MARK_EXC_IP_SELECTIVE();
// Arriving here, there's "exception control block" on top of stack,
- // and __exit__ bound method underneath it. Bytecode calls __exit__,
+ // and __exit__ method (with self) underneath it. Bytecode calls __exit__,
// and "deletes" it off stack, shifting "exception control block"
// to its place.
- static const mp_obj_t no_exc[] = {mp_const_none, mp_const_none, mp_const_none};
if (TOP() == mp_const_none) {
- sp--;
- mp_obj_t obj = TOP();
+ // stack: (..., __exit__, ctx_mgr, None)
+ sp[1] = mp_const_none;
+ sp[2] = mp_const_none;
+ sp -= 2;
+ mp_call_method_n_kw(3, 0, sp);
SET_TOP(mp_const_none);
- mp_call_function_n_kw(obj, 3, 0, no_exc);
} else if (MP_OBJ_IS_SMALL_INT(TOP())) {
mp_int_t cause_val = MP_OBJ_SMALL_INT_VALUE(TOP());
if (cause_val == UNWIND_RETURN) {
- mp_call_function_n_kw(sp[-2], 3, 0, no_exc);
+ // stack: (..., __exit__, ctx_mgr, ret_val, UNWIND_RETURN)
+ mp_obj_t ret_val = sp[-1];
+ sp[-1] = mp_const_none;
+ sp[0] = mp_const_none;
+ sp[1] = mp_const_none;
+ mp_call_method_n_kw(3, 0, sp - 3);
+ sp[-3] = ret_val;
+ sp[-2] = MP_OBJ_NEW_SMALL_INT(UNWIND_RETURN);
} else {
assert(cause_val == UNWIND_JUMP);
- mp_call_function_n_kw(sp[-3], 3, 0, no_exc);
- // Pop __exit__ boundmethod at sp[-3]
- sp[-3] = sp[-2];
+ // stack: (..., __exit__, ctx_mgr, dest_ip, num_exc, UNWIND_JUMP)
+ mp_obj_t dest_ip = sp[-2];
+ mp_obj_t num_exc = sp[-1];
+ sp[-2] = mp_const_none;
+ sp[-1] = mp_const_none;
+ sp[0] = mp_const_none;
+ mp_call_method_n_kw(3, 0, sp - 4);
+ sp[-4] = dest_ip;
+ sp[-3] = num_exc;
+ sp[-2] = MP_OBJ_NEW_SMALL_INT(UNWIND_JUMP);
}
- sp[-2] = sp[-1]; // copy retval down
- sp[-1] = sp[0]; // copy cause down
- sp--; // discard top value (was cause)
+ sp -= 2; // we removed (__exit__, ctx_mgr)
} else {
assert(mp_obj_is_exception_type(TOP()));
+ // stack: (..., __exit__, ctx_mgr, traceback, exc_val, exc_type)
// Need to pass (sp[0], sp[-1], sp[-2]) as arguments so must reverse the
// order of these on the value stack (don't want to create a temporary
// array because it increases stack footprint of the VM).
mp_obj_t obj = sp[-2];
sp[-2] = sp[0];
sp[0] = obj;
- mp_obj_t ret_value = mp_call_function_n_kw(sp[-3], 3, 0, &sp[-2]);
+ mp_obj_t ret_value = mp_call_method_n_kw(3, 0, sp - 4);
if (mp_obj_is_true(ret_value)) {
- // This is what CPython does
- //PUSH(MP_OBJ_NEW_SMALL_INT(UNWIND_SILENCED));
- // But what we need to do is - pop exception from value stack...
+ // We need to silence/swallow the exception. This is done
+ // by popping the exception and the __exit__ handler and
+ // replacing it with None, which signals END_FINALLY to just
+ // execute the finally handler normally.
sp -= 4;
- // ... pop "with" exception handler, and signal END_FINALLY
- // to just execute finally handler normally (by pushing None
- // on value stack)
+ SET_TOP(mp_const_none);
assert(exc_sp >= exc_stack);
POP_EXC_BLOCK();
- PUSH(mp_const_none);
} else {
- // Pop __exit__ boundmethod at sp[-3], remembering that top 3 values
- // are reversed.
- sp[-3] = sp[0];
- obj = sp[-2];
- sp[-2] = sp[-1];
- sp[-1] = obj;
- sp--;
+ // We need to re-raise the exception. We pop __exit__ handler
+ // and copy the 3 exception values down (remembering that they
+ // are reversed due to above code).
+ sp[-4] = sp[0];
+ sp[-3] = sp[-1];
+ sp -= 2;
}
}
DISPATCH();