Rewrite can_derive_debug as either a graph traversal or fix-point analysis

[fitzgen]

See #536 for details.

[photoszzt]

While I'm waiting things to compile, I wrote part of this following the skeleton in #765 in photoszzt@9e170ae. I also separate the MonotoFramework to the other file (photoszzt@718d367).

Looking at the skeleton code, I'm not sure where the consider_edge is used.

[fitzgen]

@highfive assign @photoszzt

[fitzgen]

Hmm, I guess highfive bot doesn't let you assign other people, and I can't assign either. Ah well.

Anyways, cool! :)

The commit separating the analysis infrastructure to its own file can land now, if you want to make a PR with just that commit.

The consider_edge function would be used to filter edges from the IR graph that don't matter for this analysis, and would be called when constructing the reversed graph for dependencies. Did you take a look at its use in the UsedTemplateParams analysis? That should hopefully help clear things up.

Easiest way for me to provide feedback on the CanDeriveDebugAnalysis would be to open a PR so I can leave comments inline easily.

[KiChjang]

FTR, @highfive assign me doesn't actually do anything facy behind the scenes, all it does is add a C-assigned tag to the issue, so if you do want to "assign" an issue to someone else, you can simply put the C-assigned tag on the issue manually.

[fitzgen]

FTR, @highfive assign me doesn't actually do anything facy behind the scenes, all it does is add a C-assigned tag to the issue, so if you do want to "assign" an issue to someone else, you can simply put the C-assigned tag on the issue manually.

Huh. It seems the "assigned" field is pretty useless then...