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

[via llvm-commits]

yonghong-song wrote:

> Yes that lets us describe the multiple variations.
> 
> One point my suggestions does _not_ address: which functions should be callable from the debugger, and which not callable? If the original function `foo` should not be callable (because it uses one of the modified parameter lists), we haven't done anything to indicate that. I think @dwblaikie was suggesting using the calling convention, would that work? Or do we need something else?

@pogo59 For my above example,
```
DW_TAG_subprogram
                DW_AT_low_pc	(0x0000000100003ed8)
                DW_AT_high_pc	(0x0000000100003f18)
                DW_AT_frame_base	(...)
                DW_AT_name	("foo")

                DW_TAG_formal_parameter
                   DW_AT_name	("a")
                   DW_AT_type	(0x0000000000000091 "int")

                DW_TAG_formal_parameter
                   DW_AT_location
                   DW_AT_name	("b")
                   DW_AT_type	(0x0000000000000095 "float")

                DW_TAG_formal_parameter
                   DW_AT_location
                   DW_AT_name	("c")
                   DW_AT_type	(0x0000000000000025 "char")

NULL

       DW_TAG_inlined_subroutine
                DW_AT_name	("foo")    
                DW_AT_type	(0x0000000000000091 "int")
                DW_AT_artificial (true)
                DW_AT_specificiation (original DW_TAG_subprogram)

                DW_TAG_formal_parameter
                  DW_AT_name	("b")
                  DW_AT_type	(0x0000000000000091 "int")

               DW_TAG_formal_parameter
                  DW_AT_name	("c")
                  DW_AT_type	(0x0000000000000095 "float")

       DW_TAG_inlined_subroutine
                DW_AT_name	("foo.1")    
                DW_AT_type	(0x0000000000000091 "int")
                DW_AT_artificial (true)
                DW_AT_specificiation (original DW_TAG_subprogram)

                DW_TAG_formal_parameter
                  DW_AT_name	("b")
                  DW_AT_type	(0x0000000000000091 "int")
```

I assume two functions with DW_TAG_inlined_subroutine should be callable for debugger?
We do have some calling conventions in llvm:
  https://github.com/llvm/llvm-project/blob/main/llvm/include/llvm/BinaryFormat/Dwarf.def#L1096-L1134
Not sure which one is appropriate. Any suggestions?


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