Chapter 6. Adding a --target to the genx compiler.

The genx command is actually a driver that puts together a pipeline in which the parser pass feeds the intermediate representation to the code generating pass. This command's code is in the genx subdirectory of the directory tree.

To add a target you must:

1. Make the genx program recognize your new target in the --target option.

2. Make the genx program build the correct pipeline for your new target.

genx uses gengetopt to process command parameters. gengetopt takes genxparams.ggo as input and creates a header and C file to parse the parameters and options. Locate the following line in that file:

option "target" t "Code generation target" values="spectcl","root" enum
				

Add your target name to the list of target names in the values clause of this line.

Next you'll need to modify the genx.cpp compiler driver to select the correct backend for your option. Suppose your new target is called mytarget and is implemented in a program named mygenerator that will be installed in the genx installation's bin directory.

Locate the following code snippet in genx.cpp:

    if (parsedArgs.target_arg == target_arg_spectcl) {
        backend += "specgenerate";
    } else {
        backend += "rootgenerate";
    }
				

Modify it to look like:

    if (parsedArgs.target_arg == target_arg_spectcl) {
        backend += "specgenerate";
    } else if (parsedArgs.target_arg == target_arg_root) {
        backend += "rootgenerate";
    } else if (parsedArgs.target_arg == target_arg_mytarget) {
				    backent += "mygenerator";
				}

				

Note that since gengetop's parameter parsing code ensures the value of --target is one of the values specified, there's no need (though it can't hurt) for a final else to report an illegal value.