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gh-124265: Remove redundant if statements in traceback.c #124272

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c2f7861
Remove redundant if statements in traceback.c
rruuaanng Sep 20, 2024
43dab5c
Merge branch 'main' into 124265
skirpichev Sep 20, 2024
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3 changes: 0 additions & 3 deletions Python/traceback.c
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Original file line number Diff line number Diff line change
Expand Up @@ -980,9 +980,6 @@ dump_traceback(int fd, PyThreadState *tstate, int write_header)
/* Trampoline frame */
frame = frame->previous;
}
if (frame == NULL) {
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Why, but why do you think that frame->previous on L981 is not NULL?

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@rruuaanng rruuaanng Sep 20, 2024 •
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If frame is part of a chain and there might be a situation where it’s traversed backwards, then at that point in the code

cpython/Python/traceback.c

Line 975 in 7a2d77c

frame = frame->previous;

It should break out. That’s what I think.
I’m not sure if my description is accurate. it’s just how I imagine the situation.

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@rruuaanng rruuaanng Sep 20, 2024 •
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static void
dump_traceback(int fd, PyThreadState *tstate, int write_header)
{
    if (write_header) {
        PUTS(fd, "Stack (most recent call first):\n");
    }

    if (tstate_is_freed(tstate)) {
        PUTS(fd, "  <tstate is freed>\n");
        return;
    }

    _PyInterpreterFrame *frame = tstate->current_frame;
    if (frame == NULL) {
        PUTS(fd, "  <no Python frame>\n");
        return;
    }

    unsigned int depth = 0;
    while (1) {
        if (MAX_FRAME_DEPTH <= depth) {
            if (MAX_FRAME_DEPTH < depth) {
                PUTS(fd, "plus ");
                _Py_DumpDecimal(fd, depth);
                PUTS(fd, " frames\n");
            }
            break;
        }
        dump_frame(fd, frame);
        frame = frame->previous;
        if (frame == NULL) {
            break;
        }
        if (frame->owner == FRAME_OWNED_BY_CSTACK) {
            /* Trampoline frame */
            frame = frame->previous;
        }
        // if (frame == NULL) {
        //     break;
        // }
        /* Can't have more than one shim frame in a row */
        assert(frame->owner != FRAME_OWNED_BY_CSTACK);
        depth++;
    }
}

I hid the targets I needed to modify by commenting them out.

cpython/Python/traceback.c

Lines 983 to 985 in 7a2d77c

if (frame == NULL) {
break;
}

Then run PCbuild/build.bat, I then ran the tests using ./python Lib\test\test_traceback.py.
It seemed to run well as it passed all 347 tests in about 8.3 seconds.

PS E:\code\cc\cpython\alpha\cpython-main> ./python .\Lib\test\test_traceback.py
Running Debug|x64 interpreter...
...........................................................................................................................................................................................................................................................................................................................................................
----------------------------------------------------------------------
Ran 347 tests in 8.303s

OK

But I can't understand why it fails on CI. Maybe I ran the test incorrectly.

break;
}
/* Can't have more than one shim frame in a row */
assert(frame->owner != FRAME_OWNED_BY_CSTACK);
depth++;
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