Piezo, PIFOTree: static option!

[anshumanmohan]

We now have a variant of the PIFOtree-controller-dataplane setup (hereby dubbed "SDN", somewhat grandly) where the stats component is static.

I have made small improvements to the eDSL library, adding static variants as needed. The goal was to continue to do everything through builder.py, never needing to directly access the Calyx AST. I've been successful in that. Other programs could eventually use my new additions for cleaner code.

Overall this looks successful to me: the static version is producing the same output as the dynamic version upon being fed 100 commands.

[anshumanmohan]

@rachitnigam just tagging you in case you see an easy way to reengineer the runt clumsiness.

1. Re: -d well-formed:
   I know how to pass a bespoke flag to a "glob" of files, frequently a directory. But is there any way, within a directory (in this case [calyx-py] correctness), to pass a special Calyx flag to one file?

2. Re: --static:
   Maybe this was a poor idea, and I should just have a separate .py, .data, .expect trio?

[anshumanmohan]

It would have been nice to have reused the existing incr with a static flag as an argument. I got a good way through it, but then the issue is that the dynamic version needs a line incr_group.done = ... but the static version does not.

I'd usually do that with the Python idiom of X if b else Y, but that doesn't tango super well with the eDSL's own with foo as bar: baz idiom.

[anshumanmohan]

Just paging @sampsyo in case he knows a neat way! Like basically is there some Y such that I could do:

with foo as bar:
  ...
  ...
  X if not static else Y

and the Y would be a no-op, ignored when generating Calyx code?

If I had a nice way of doing this, I could go through and do it for lots of helpers in the eDSL!

[anshumanmohan]

Thank you for the sync chat; it worked like a charm!

[rachitnigam]

Regarding the runt question: the easiest way to do this is define a separate test suite which only captures the glob of files that you want and passing the extra flag to it. Does that make sense?

[anshumanmohan]

For now I have just written, desugared, the code that I needed. It is easy to imagine a little sugar like:
static_if_while(CellAndGroup, IfBody, ElseBody), that:

1. Snaps apart the CellAndGroup into Cell and Group.
2. Puts all of Group's assignments into continuous assignment land.
3. Finally turns itself into static_if(Cell.out, IfBody, ElseBody)

[anshumanmohan]

This is now #1785

[anshumanmohan]

@rachitnigam yes I see how this solves my -d flag issue!

Any thoughts about the --static issue? Should I just bite the bullet and make a separate trio of files for static PIFO trees? And then the bespoke glob would hunt down that new static trio? Cuz right now, the runt command that is running on branch push is just testing the dynamic version! Runt doesn't know anything about this weird --static flag.

[rachitnigam]

Sorry, what does the --static flag do? If its supposed to generate the same output files but have a different implementation running and you want to do differential testing, you can use the expect_dir field in the test suite configuration to specify the location of the output file.

[anshumanmohan]

Thanks Rachit! Yes so the --static flag changes out the guts of the stats component to be static, and also changes the one invoke of the stats component into a static invoke.

For now I have just gone with a new trio of files (sdn.{py, data, expect}), living in their own directory (calyx-py/test/correctness/static/). This was the easiest way to define a glob for runt. Differential testing against the dynamic version is exactly the right idea, but I'm running into a silly engineering bugaboo that we can leave for post-deadline maybe?

[anshumanmohan]

I have updated the frontmatter of the PR to reflect the latest state of affairs. I think this is ready for review.