[mypyc] handle negative_int_emit and Truncate op

[TH3CHARLie]

related mypyc/mypyc#734

[TH3CHARLie]

There will be auto-generated Box, Unbox, DecRef sequence right after the CallC which I don't expect to have.

in the following code's case, this sequence will try to check whether the return value from CallC is a boolean.

def foo(x: object) ->bool:
    z = isinstance(x, str)
    return z

Since int32_rprimitive is an unboxed type, this would lead to an assertion failure during emit.

update:
fixed

[TH3CHARLie]

With this PR, for the following python function:

def foo(x: object) -> bool:
    z = isinstance(x, str)
    return z

The C code before:

char CPyDef_foo(PyObject *cpy_r_x) {
    PyObject *cpy_r_r0;
    char cpy_r_r1;
    char cpy_r_z;
    char cpy_r_r2;
CPyL0: ;
    cpy_r_r0 = (PyObject *)&PyUnicode_Type;
    int __tmp1 = PyObject_IsInstance(cpy_r_x, cpy_r_r0);
    if (__tmp1 < 0)
        cpy_r_r1 = 2;
    else
        cpy_r_r1 = __tmp1;
    if (unlikely(cpy_r_r1 == 2)) {
        CPy_AddTraceback("../foo.py", "foo", 2, CPyStatic_globals);
        goto CPyL2;
    } else
        goto CPyL1;
CPyL1: ;
    cpy_r_z = cpy_r_r1;
    return cpy_r_z;
CPyL2: ;
    cpy_r_r2 = 2;
    return cpy_r_r2;
}

after:

char CPyDef_foo(PyObject *cpy_r_x) {
    PyObject *cpy_r_r0;
    int32_t cpy_r_r1;
    char cpy_r_r2;
    char cpy_r_z;
    char cpy_r_r3;
CPyL0: ;
    cpy_r_r0 = (PyObject *)&PyUnicode_Type;
    cpy_r_r1 = PyObject_IsInstance(cpy_r_x, cpy_r_r0);
    if (unlikely(cpy_r_r1 < 0)) {
        CPy_AddTraceback("../foo.py", "foo", 2, CPyStatic_globals);
        goto CPyL2;
    } else
        goto CPyL1;
CPyL1: ;
    cpy_r_r2 = cpy_r_r1;
    cpy_r_z = cpy_r_r2;
    return cpy_r_z;
CPyL2: ;
    cpy_r_r3 = 2;
    return cpy_r_r3;
}

We actually reduce the comparison by 1 even though we introduce a new op in its IR.

[JukkaL]

Looks good! Left a few comments about documentation.

[TH3CHARLie]

Once this is merged, I'd start to merge the remaining ops during the weekends.

[JukkaL]

Thanks!