[llvm] [Utils][update_mc_test_checks] Support generating asm tests from templates. (PR #168946)

[Ivan Kosarev via llvm-commits]

https://github.com/kosarev commented:

Added a test.

There are obviously lots of things about this that will likely need more work, such as maybe expanding tokens beginning the longest ones, for one example. I intentionally postpone addressing them until later, when we have a better idea on what it's like to use templates in practice.

> Btw, does this "regenerate from template" feature remove the existing test lines?

Yes, the idea is that where templates are used, they work as the single source of input, meaning the reader should never need to consult the rest of the file. Doing otherwise would undermine the idea of having templates as a comprehensible but true version of the test.

https://github.com/llvm/llvm-project/pull/168946