Open
Description
There seems to be a bug when checking if an action can be run in parallel during VerifyInstructionParams pass in instruction_selection.cpp.
Here is an example:
action error_trigger_1(mac_addr_t srcMac, PortId_t dst_port_4, bit<16> tmp) {
hdr.ethernet.ether_type = 1 + (tmp - 1);
}
@name("SwitchIngress.forward") table forward_0 {
key = {
}
actions = {
error_trigger_1();
}
}
Error message:
[--Werror=unsupported] error: add: action spanning multiple stages. Operations on operand 3 ($tmp7[0..15]) in action error_trigger_1 require multiple stages for a single action. We currently support only single stage actions. Please rewrite the action to be a single stage action.
hdr.ethernet.ether_type = 1 + (tmp - 1);
This does not just happen to add, but other instructions like shl, sub, xor, saddu, and so on.
A possible cause is, Tofino BE cannot correctly assign $tmp to expressions, and constructs scenarios where a tmp is used in a way that causes a statement cannot run in parallel.
However, if we change the line to hdr.ethernet.ether_type = (tmp - 1) + 1;, then there is no error reported.
I also tried non-action-data, which obey the similar behavior, like hdr.ethernet.ether_type = -hdr.ipv4.hdr_checksum + 1; cause the same issue.