[llvm] [KeyInstr][DwarfDebug] Add is_stmt emission support (PR #133495)

[Orlando Cazalet-Hyams via llvm-commits]

https://github.com/OCHyams commented:

Tests: I'd personally prefer the input source and explanation at the top of the file, although this is a style thing.

> Done

> My understanding of this code is that within a basic block, it should be possible for there to be two sequences of instructions of equal group and rank that both get a buoy and is_stmt, if they're separated by some other atom group. Perhaps I'm wrong; but if I'm right, it probably wants explicit test coverage.

That is tested in `dwarf-buoy-multi-key.mir` (but was broken, now fixed).

> There's a risk that the code being generated is brittle and frequently needs updating; I don't know what probability of that we find acceptable, let's just see how often it needs updating I guess.

The tests are not fun to read and were not fun to write, and probably won't be particularly fun to maintain as you have pointed out. Not sure this can be massively improved with the current strategy and I couldn't think of a different way to test it, sadly.

https://github.com/llvm/llvm-project/pull/133495