p4c: Follow-up issue on exit statements

As @jafingerhut pointed out in #2225 , there might be some fallout from the exit changes. One of them is an edge-case in how to handle SideEffectOrdering.

SideEffectOrdering transforms the following program:

control ingress(inout Headers h, inout Meta m, inout standard_metadata_t sm) {
    action NoAction() {
    }
    action call_exit(inout bit<48> val, in bit<48> val1) {
            val = 1;
            exit;
    }
    apply {
        call_exit(h.eth_hdr.src_addr, h.eth_hdr.src_addr);
    }
}

into

control ingress(inout Headers h, inout Meta m, inout standard_metadata_t sm) {
    @name("call_exit") action call_exit_0(inout bit<48> val, in bit<48> val1) {
        val = 48w1;
        exit;
    }
    bit<48> tmp;
    bit<48> tmp_0;
    apply {
        {
            tmp = h.eth_hdr.src_addr;
            tmp_0 = h.eth_hdr.src_addr;
            call_exit_0(tmp, tmp_0);
            h.eth_hdr.src_addr = tmp;
        }
    }
}

which still looks okay, but ultimately this change causes this transformation in the MidEnd pass RemoveActionParameters:

control ingress(inout Headers h, inout Meta m, inout standard_metadata_t sm) {
    bit<48> tmp;
    bit<48> tmp_0;
    bit<48> val;
    bit<48> val1;
    @name("ingress.call_exit") action call_exit() {
        val = tmp;
        val1 = tmp_0;
        val = 48w1;
        tmp = val;
        exit;
        tmp = val;
    }
    apply {
        tmp = h.eth_hdr.src_addr;
        tmp_0 = h.eth_hdr.src_addr;
        call_exit();
        h.eth_hdr.src_addr = tmp;
    }
}

Here, h.eth_hdr.src_addr will never be assigned the value 1, from what I can tell.

side_effect_ordering_exit.p4.txt side_effect_ordering_exit.stf.txt