This essentially passes the members of a linear map tuple as individual arguments. It yields few nice simplifications:
* No linear map tuples at all for getters / setters
* No tuple formation / deconstruction around pullbacks
* Pullbacks with loops still use heap-allocated tuples
The changes are intentionally were made close to the original implementation w/o possible simplifications to ease the review
Fixes#63207, supersedes #63379 (and fixes#63234)
Single input variable might yield multiple adjoint buffers if control flow is involved. Therefore we cannot simply transfer debug info from the input variable: it will be invalid as we will end with multiple locations for a single "source" variable, and, even worse, might end with conflicting debug info as different buffers might be optimized
differently.
We do:
- Drop input argument number. This must be unique and we're not
- Correct variable name
`salvageDebugInfo` is called during SIL Mem2Reg and could produce misleading debug info in the following case:
```
%a = alloc_stack $MyModel.TangentVector, var, name "self", argno 1, implicit, loc "debug2.swift":37:17 ...
...
store %b to %a : $*MyModel.TangentVector
```
Such SIL could be created as a result of inlining (where store comes from the inlined function).
Before this patch we'd end with `debug_value` instruction with variable information, but without or incorrect location.
This caused LLVM IR debug info verifier assertions when there might be another instruction with complete debug info (including location) for the same argument.
After this patch we always reuse it from destination alloca
Fixes#58660
