Convert TODOs to GH Issues

[f0rki]

• in casts: Document pointer-to-integer casts. see Document usage ptrtoint/inttoptr instructions #8
• in casts: Document integer-to-pointer casts. see Document usage ptrtoint/inttoptr instructions #8
• in casts: Find a useful example of an address-space casts, using the addrspacecast instruction, to be included here. see Document address space casts #11
• in structure-expressions: Document the extractvalue and insertvalue instructions.
• in mapping-control-structures-to-llvm-ir: Add common control structures such as if, for, switch, and while. see Basic Control Structures #6
• in mapping-control-structures-to-llvm-ir: Explain the purpose of the phi instruction; see Basic Control Structures #6
• in closures: Describe closures. see Describe closures #5
• in zero-cost-exception-handling: Explain how to implement exception handling using zero cost exception handling. see Document zero-cost exception handling #10
• in class-equivalence-test: Finish up class equivalence test sample.
• in class-inheritance-test: Document the faster class inheritance test implementation.
• from appendix-b-task-list: Ask various front-end implementors (Rust, Haskell (GHC), Rubinius, and more) to review and/or contribute so as to make the document great.

[minghu6]

It seems that this plan is a little outdated?

https://github.com/f0rki/mapping-high-level-constructs-to-llvm-ir/issues/mapping-exception-handling-to-llvm-ir/zero-cost-exception-handling.md has moved to .rst format, And It's still an empty file (just a Title), the target isn't completed indeed.

[archfrog]

I don't know about Michael (f0rki), but I have no knowledge of zero-cost exceptions. I wrote the initial document many years ago, and I don't seriously expect to ever cover zero-cost exceptions. I guess it is up to somebody with expertise in the area to complete that chapter. Back then, I expected to study zero-cost exceptions, but I've long ago dropped that idea again.

Basically, I wrote the document and gave it up because of other, more pressing concerns. So far, nobody has expanded significantly upon it since and it sorts of lives its own life, perhaps helping newcomers to LLVM a bit, but that's pretty much it.

[f0rki]

Unfortunately, I have never found the time to actively expand this document. I try to quickly merge PRs, fix small things, etc. though. It helped me a lot when starting with llvm so I try to keep it online.

This issue is solely meant to track converting open todos from the original document of @archfrog to github issues. There is already issue #10 regarding zero-cost exception handling. Feel free to drop any helpful resources there. We can also start to collect some helpful links/resources in that chapter as a start.

(I updated the links in this issue s.t., they don't 404)