[llvm] [Dwarf][Transforms] Add dwarf support when func signature changed (PR #127855)

[Jose E. Marchesi via llvm-commits]

jemarch wrote:

> > Wouldn't it be possible to set the existing DW_AT_artificial attribute instead of introducing vendor-specific extensions?
> 
> not sure if that'd connote either of the properties being expressed here (uncallable, and un-printable-returns) - for instance in C++, implicit ctors, assignment operators, and dtors are artificial but callable/printable returns based on ABI, so we couldn't have debuggers assuming artificial functions can't be called/have their return values printed.

The idea, which we were briefly discussing today in the #gcc IRC channel, would be to have the signature change of some given function represented in DWARF using a DW_TAG_artificial "container" with an inlined subroutine reflecting the original signature.  Something like: 

```
foo.clone (int a, int b) { foo (1, { a, b }); } 
```

The signature change would be described in the formal parameters of the DW_TAG_inlined_subroutine.


https://github.com/llvm/llvm-project/pull/127855