Remove ReferenceMap from top-level frontend passes

[asl]

Finally, this removes ReferenceMap from top-level frontend passes:

• RemoveAllUnusedDeclarations uses lightweight implementation of used set that was factored out from ResolveReferences
• Added shortcut CheckShadow to execute ResolveReferences with shadow check enabled (and with "local" refmap)
• Made refmap and internal implementation details of Evaluator, Inliner and SimplifyDefUse

[asl]

As Evaluator is an inspector, presumably running it does not change anything, do we even need it in Frontend? Or is it because of errors it can produce? There seems to be just one...

Yeah, I was confused as well. And applied the common logic: if something looks incomplete, then probably there is a downstream code that uses / changes this. So, I tried to keep the existing logic as much as possible.

The Evaluator itself is a bit special:

• It does its own traversal
• While it is an Inspector, it creates new nodes. Though, it does not attach them anywhere, they are used to build a hierarchy of CompileTimeValue / Block nodes similar to CFG.

The inliner (DiscoverInlining specifically) does depend on the evaluator as it seems to traverse Block's from the top level block, not the whole program. Given that Inliner runs in PassRepeated we'd need to update that CFG re-running evaluator.

I think we'd can just remove it from Frontend, yes.

[asl]

I think I addressed the majority of review comments.

@fruffy I'm going to do TypeChecking changes in a separate PR.

[vlstill]

The inliner (DiscoverInlining specifically) does depend on the evaluator as it seems to traverse Block's from the top level block, not the whole program. Given that Inliner runs in PassRepeated we'd need to update that CFG re-running evaluator.

Oh, I missed that inliner runs as PassRepeated, sorry.

[asl]

Looks like both bazel and fedora are unhealthy. @grg @fruffy do you know what's going on?

[fruffy]

Looks like both bazel and fedora are unhealthy. @grg @fruffy do you know what's going on?

It's possible that one of the new includes is breaking the Bazel build related to alloc_trace. For Fedora, unclear how that error happens. Hope it is spurious.

[fruffy]

@smolkaj Any idea whether the Bazel failures are spurious or require a change?

[asl]

@fruffy @smolkaj Bazel seems to be recovered. Only Fedora left...