IL Checker about jeff65 HOT 1 OPEN

As far as I can tell, NFCE just has the passes run in a predefined order, but we can probably make things more complicated than that.

For starters, the fact that simplification and conversion passes change the IR implies a kind of sequential grouping. "Phase" is kind of an overloaded term, so let's call the set of all operations to be done on a particular IR an "era". Each era ends with a simplification pass or conversion pass (or outputting to disk).

Now, if we consider a DAG where each era is a node, and each conversion/simplification pass is an edge, we can, given a target and a starting point, automatically determine an appropriate sequence of conversion/simplification passes. The compiler should (at least in debug mode) verify that only one such path is possible. We then filter out any passes which are unused in this path, including verification, analysis, and improvement passes associated with off-path eras.

Now we construct a new DAG, this time including all passes. We assume that any additional inter-pass dependencies have been annotated appropriately. The resulting DAG can then be topologically sorted, and the resulting sequence used to execute the compilation.

This can be extended, incidentally, to handle automatic recursive compilation, and provides us with a convenient method of handling multiple targets too. Such usage will require that, rather than simply constructing a sequence to be executed, we also consider that passes will be run multiple times on different inputs.

from jeff65.