Replace hilariously out of date backend architecture document

[thewilsonator]

Also on that subject why do we have two AA implementations, another leaking allocator, that leaks from malloc instead of the GC?

[dlang-bot]

Thanks for your pull request and interest in making D better, @thewilsonator! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.
Please verify that your PR follows this checklist:

• My PR is fully covered with tests (you can see the annotated coverage diff directly on GitHub with CodeCov's browser extension
• My PR is as minimal as possible (smaller, focused PRs are easier to review than big ones)
• I have provided a detailed rationale explaining my changes
• New or modified functions have Ddoc comments (with Params: and Returns:)

Please see CONTRIBUTING.md for more information.

---

If you have addressed all reviews or aren't sure how to proceed, don't hesitate to ping us with a simple comment.

Bugzilla references

Your PR doesn't reference any Bugzilla issue.

If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + dmd#9850"

[thewilsonator]

@WalterBright can we:

• rm backend/aarray.d and replace its uses with root/aav.d?
• rm backend/outbuf.d and replace it with root/outbuffer?
• rm backend/ph2.d and leak from just the GC?
• mv complex.d root/complex.d && rm backend/bcomplex.d?

[jacob-carlborg]

This looks pretty awful when it’s rendered: https://github.com/thewilsonator/dmd/blob/d38197fe1734cd03961bcb322b9fd926eafccebb/src/dmd/backend/backend.md

[jacob-carlborg]

I don’t think Walter want the backend to use the root package. Although I thought the reason for having the root package was for the frontend and backend to share code.

[thewilsonator]

Ow, yeah that it a horrible rendering (looks much nicer in plain text, lol). Fixed.

[thewilsonator]

Yes, a list looks much better.

[jacob-carlborg]

Perhaps make the filenames bold as well. Or otherwise somehow separate the filename from the description.

[thewilsonator]

Im about to go to sleep, don't let me stop you doing that ;)