cartesian: report write-only temporaries

[romanc]

Description

In stencils, any unknown variable is automatically assumed to be a temporary. In the context of NWP codes with cryptic argument names, it can easily happen that an "output argument" is misspelled. In that case, the variable is a temporary. In this case, we get faulty behavior and potentially needlessly allocated memory. We could detect scenarios where temporaries are written and not read afterwards. Such cases could be flagged and reported (as warnings/errors) to users of GT4Py.

The current behavior is that this kind of situation is undetected at the GT4Py level. Once code is generated, the underlying compiler of the target language of the backend might or might not raise warnings.

Example

Notice how qcu_s, qlu_s, qiu_s, xc_s, cin_s, cinlcl_s, cbmf_s, and qc_s are allocated as temporaries in the following stencil.

def adjust_implicit_CIN_inputs2(
    condensation: BoolFieldIJ,
    umf_s: FloatField,
    umf_zint: FloatField,
    dcm: FloatField,
    qrten: FloatField,
    qsten: FloatField,
    cush: FloatFieldIJ,
    cufrc: FloatField,
    slflx_s: FloatField,
    slflx: FloatField,
    qtflx_s: FloatField,
    qtflx: FloatField,
    uflx_s: FloatField,
    uflx: FloatField,
    vflx_s: FloatField,
    vflx: FloatField,
    qcu: FloatField,
    qlu: FloatField,
    qiu: FloatField,
    fer: FloatField,
    fdr: FloatField,
    xco: FloatField,
    cin_IJ: FloatFieldIJ,
    cinlcl_IJ: FloatFieldIJ,
    cbmf: FloatField,
    qc: FloatField,
    qlten_det: FloatField,
    qiten_det: FloatField,
    qlten_sink: FloatField,
    qiten_sink: FloatField,
    ufrc_s: FloatField,
    ufrc: FloatField,
    dcm_s: FloatField,
    qrten_s: FloatField,
    qsten_s: FloatField,
    qldet_s: FloatField,
    qidet_s: FloatField,
    qlsub_s: FloatField,
    qisub_s: FloatField,
    cush_s: FloatField,
    cufrc_s: FloatField,
    fer_s: FloatField,
    fdr_s: FloatField,
    iteration: int32,
):
    """
    Part II of Adjust Implicit CIN Inputs
    """

    with computation(FORWARD), interval(...):
        if not condensation:
            umf_s = umf_zint
            umf_s[0, 0, 1] = umf_zint[0, 0, 1]
            dcm_s = dcm
            qrten_s = qrten
            qsten_s = qsten
            cush_s = cush
            cufrc_s = cufrc
            slflx_s = slflx
            qtflx_s = qtflx
            uflx_s = uflx
            vflx_s = vflx
            slflx_s[0, 0, 1] = slflx[0, 0, 1]
            qtflx_s[0, 0, 1] = qtflx[0, 0, 1]
            uflx_s[0, 0, 1] = uflx[0, 0, 1]
            vflx_s[0, 0, 1] = vflx[0, 0, 1]
            qcu_s = qcu
            qlu_s = qlu
            qiu_s = qiu
            fer_s = fer
            fdr_s = fdr
            xc_s = xco
            cin_s = cin_IJ
            cinlcl_s = cinlcl_IJ
            cbmf_s = cbmf
            qc_s = qc
            qldet_s = qlten_det
            qidet_s = qiten_det
            qlsub_s = qlten_sink
            qisub_s = qiten_sink

            ufrc_s = ufrc
            ufrc_s[0, 0, 1] = ufrc[0, 0, 1]