py/vm: Optimise handling of stackless mode when pystack is enabled.

When pystack is enabled mp_obj_fun_bc_prepare_codestate() will always
return a valid pointer, and if there is no more pystack available then it
will raise an exception (a RuntimeError).  So having pystack enabled with
stackless enabled automatically gives strict stackless mode.  There is
therefore no need to have code for strict stackless mode when pystack is
enabled, and this patch optimises the VM for such a case.

py/vm.c

@@ -911,21 +911,22 @@ unwind_jump:;
                         code_state->sp = sp;
                         code_state->exc_sp = MP_TAGPTR_MAKE(exc_sp, currently_in_except_block);
                         mp_code_state_t *new_state = mp_obj_fun_bc_prepare_codestate(*sp, unum & 0xff, (unum >> 8) & 0xff, sp + 1);
-                        if (new_state) {
+                        #if !MICROPY_ENABLE_PYSTACK
+                        if (new_state == NULL) {
+                            // Couldn't allocate codestate on heap: in the strict case raise
+                            // an exception, otherwise just fall through to stack allocation.
+                            #if MICROPY_STACKLESS_STRICT
+                        deep_recursion_error:
+                            mp_raise_recursion_depth();
+                            #endif
+                        } else
+                        #endif
+                        {
                             new_state->prev = code_state;
                             code_state = new_state;
                             nlr_pop();
                             goto run_code_state;
                         }
-                        #if MICROPY_STACKLESS_STRICT
-                        else {
-                        deep_recursion_error:
-                            mp_raise_recursion_depth();
-                        }
-                        #else
-                        // If we couldn't allocate codestate on heap, in
-                        // non non-strict case fall thru to stack allocation.
-                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_function_n_kw(*sp, unum & 0xff, (unum >> 8) & 0xff, sp + 1));
@@ -956,20 +957,21 @@ unwind_jump:;
                         // pystack is not enabled.  For pystack, they are freed when code_state is.
                         mp_nonlocal_free(out_args.args, out_args.n_alloc * sizeof(mp_obj_t));
                         #endif
-                        if (new_state) {
+                        #if !MICROPY_ENABLE_PYSTACK
+                        if (new_state == NULL) {
+                            // Couldn't allocate codestate on heap: in the strict case raise
+                            // an exception, otherwise just fall through to stack allocation.
+                            #if MICROPY_STACKLESS_STRICT
+                            goto deep_recursion_error;
+                            #endif
+                        } else
+                        #endif
+                        {
                             new_state->prev = code_state;
                             code_state = new_state;
                             nlr_pop();
                             goto run_code_state;
                         }
-                        #if MICROPY_STACKLESS_STRICT
-                        else {
-                            goto deep_recursion_error;
-                        }
-                        #else
-                        // If we couldn't allocate codestate on heap, in
-                        // non non-strict case fall thru to stack allocation.
-                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_method_n_kw_var(false, unum, sp));
@@ -993,20 +995,21 @@ unwind_jump:;
                         int adjust = (sp[1] == MP_OBJ_NULL) ? 0 : 1;
 
                         mp_code_state_t *new_state = mp_obj_fun_bc_prepare_codestate(*sp, n_args + adjust, n_kw, sp + 2 - adjust);
-                        if (new_state) {
+                        #if !MICROPY_ENABLE_PYSTACK
+                        if (new_state == NULL) {
+                            // Couldn't allocate codestate on heap: in the strict case raise
+                            // an exception, otherwise just fall through to stack allocation.
+                            #if MICROPY_STACKLESS_STRICT
+                            goto deep_recursion_error;
+                            #endif
+                        } else
+                        #endif
+                        {
                             new_state->prev = code_state;
                             code_state = new_state;
                             nlr_pop();
                             goto run_code_state;
                         }
-                        #if MICROPY_STACKLESS_STRICT
-                        else {
-                            goto deep_recursion_error;
-                        }
-                        #else
-                        // If we couldn't allocate codestate on heap, in
-                        // non non-strict case fall thru to stack allocation.
-                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_method_n_kw(unum & 0xff, (unum >> 8) & 0xff, sp));
@@ -1037,20 +1040,21 @@ unwind_jump:;
                         // pystack is not enabled.  For pystack, they are freed when code_state is.
                         mp_nonlocal_free(out_args.args, out_args.n_alloc * sizeof(mp_obj_t));
                         #endif
-                        if (new_state) {
+                        #if !MICROPY_ENABLE_PYSTACK
+                        if (new_state == NULL) {
+                            // Couldn't allocate codestate on heap: in the strict case raise
+                            // an exception, otherwise just fall through to stack allocation.
+                            #if MICROPY_STACKLESS_STRICT
+                            goto deep_recursion_error;
+                            #endif
+                        } else
+                        #endif
+                        {
                             new_state->prev = code_state;
                             code_state = new_state;
                             nlr_pop();
                             goto run_code_state;
                         }
-                        #if MICROPY_STACKLESS_STRICT
-                        else {
-                            goto deep_recursion_error;
-                        }
-                        #else
-                        // If we couldn't allocate codestate on heap, in
-                        // non non-strict case fall thru to stack allocation.
-                        #endif
                     }
                     #endif
                     SET_TOP(mp_call_method_n_kw_var(true, unum, sp));