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GH-132554: "Virtual" iterators #132555

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Merged
merged 29 commits into from
May 27, 2025
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markshannon
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@markshannon markshannon commented Apr 15, 2025

Just a draft PR until I have performance numbers.

@markshannon
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Performance is good. Nothing amazing, but a small speedup.

Stats show no significant changes

@Fidget-Spinner
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@markshannon I don't think it matters here, but you didn't update in https://github.com/python/cpython/pull/132545/files Py_TAG_BITS to 3. It's still 1. I know it "technically" doesn't matter because we use a bitshift to zero it out, but we should still update it to be consistent.

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@markshannon I don't think it matters here, but you didn't update in https://github.com/python/cpython/pull/132545/files Py_TAG_BITS to 3. It's still 1. I know it "technically" doesn't matter because we use a bitshift to zero it out, but we should still update it to be consistent.

Fixed in #134244

static inline _PyStackRef
PyStackRef_IncrementTaggedIntNoOverflow(_PyStackRef ref)
{
assert(ref.bits != (uintptr_t)-1); // Deosn't overflow
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I don't understand why you use this condition. Should it not be assert(ref.bits + 4 > ref.bits) or something like that?

return PyCode_Check(PyStackRef_AsPyObjectBorrow(stackref));
}

static inline bool
PyStackRef_FunctionCheck(_PyStackRef stackref)
{
if (PyStackRef_IsTaggedInt(stackref)) {
return false;
}
return PyFunction_Check(PyStackRef_AsPyObjectBorrow(stackref));
}
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Would it help to define these via a macro? Something like

#define STACKREF_CHECK_FUNC(T) \
    static inline bool \
    PyStackRef_ ## T ## Check(_PyStackRef stackref) \
        if (PyStackRef_IsTaggedInt(stackref)) { \
            return false; \
        } \
        return Py ## T ## _Check(PyStackRef_AsPyObjectBorrow(stackref)); \
    }

...
STACKREF_CHECK_FUNC(Exception);
STACKREF_CHECK_FUNC(Code);
STACKREF_CHECK_FUNC(Function);

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I think it might not work when want to define variants of Check and CheckExact, though we can always define two macros for that if we go down this route.

iterable doesn't prematurely free the iterable"""

def foo(x):
r = 0
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I'd add this to make sure the test is testing what the comment is saying.
assert(sys.getrefcount(x) == 1)

_PyStackRef
PyStackRef_IncrementTaggedIntNoOverflow(_PyStackRef ref)
{
assert(ref.index != (uintptr_t)-1); // Overflow
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Do here same as in d9dc597 ?

@markshannon markshannon merged commit f6f4e8a into python:main May 27, 2025
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@markshannon markshannon deleted the virtual-iterators branch May 27, 2025 14:59
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