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[mypyc] Generate smaller code for casts by JukkaL · Pull Request #12839 · python/mypy · GitHub
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[mypyc] Generate smaller code for casts #12839

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Merged
merged 4 commits into from
May 23, 2022
Merged

[mypyc] Generate smaller code for casts #12839

merged 4 commits into from
May 23, 2022

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JukkaL
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@JukkaL JukkaL commented May 22, 2022

Merge a cast op followed by a branch that does an error check and adds a
traceback entry. Since casts are very common, this reduces the size of
the generated code a fair amount.

Old code generated for a cast:

    if (likely(PyUnicode_Check(cpy_r_x)))
        cpy_r_r0 = cpy_r_x;
    else {
        CPy_TypeError("str", cpy_r_x);
        cpy_r_r0 = NULL;
    }
    if (unlikely(cpy_r_r0 == NULL)) {
        CPy_AddTraceback("t/t.py", "foo", 2, CPyStatic_globals);
        goto CPyL2;
    }

New code:

    if (likely(PyUnicode_Check(cpy_r_x)))
        cpy_r_r0 = cpy_r_x;
    else {
        CPy_TypeErrorTraceback("t/t.py", "foo", 2, CPyStatic_globals, "str", cpy_r_x);
        goto CPyL2;
    }

The generated assembly is the same in the successful case, but assembly for the
error handler is more compact, reducing the size of binaries.

We could also do a similar thing to unbox ops in the future.

@JukkaL JukkaL merged commit 040f3ab into master May 23, 2022
@JukkaL JukkaL deleted the mypyc-cast-codegen branch May 23, 2022 14:18
@msullivan
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Great cleanup

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@ilevkivskyi ilevkivskyi ilevkivskyi approved these changes

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@JukkaL @msullivan @ilevkivskyi