[PavlNekrasov]

Widen MASK and top to int64_t before shifting

• Issue: frameobject: undefined 32-bit left shifts in stack_swap() #161666

[picnixz]

Please follow the devguide when you create a PR (gh-NNNNNN: in the title, NEWS entries).

[iRELDevz]

stack_swap() still returns Kind (32-bit), so the result gets truncated once the stack has 11+ entries, even with the casts. The return type needs to be int64_t:

-static Kind
+static int64_t
 stack_swap(int64_t stack, int n)

It's visible from Python too: this jump is wrongly rejected with can't jump into the body of a for loop (passes without the swap line). Could go into JumpTestCase in Lib/test/test_sys_settrace.py:

    def testbackwardjumpT(self):
        src = ["def f(output):"]
        src += [" " * (i + 1) + f"for a{i} in [0]:" for i in range(10)]
        src += [" " * 11 + "output.append(1)",
                " " * 11 + "output[0], a9 = a9, output[0]",
                " " * 11 + "output.append(2)"]
        ns = {}
        exec("\n".join(src), ns)
        self.run_test(ns["f"], 13, 11, [1, 1, 2])

[iRELDevz]

damn the test I suggested is too deep. 10 loops overflows the stack model and hits the top_of_stack(next_stack) == Object assert in mark_stacks on debug builds, which is what's breaking CI (it happens on main too, with or without the swap line).

6 loops is enough: it still fails on main and passes with this PR.

    def test_backward_jump_deep_stack(self):
        src = ["def f(output):"]
        src += [" " * (i + 1) + f"for a{i} in [0]:" for i in range(6)]
        src += [" " * 7 + "output.append(1)",
                " " * 7 + "output[0], a5 = a5, output[0]",
                " " * 7 + "output.append(2)"]
        ns = {}
        exec("\n".join(src), ns)
        self.run_test(ns["f"], 9, 7, [1, 1, 2])