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

[via llvm-commits]

yonghong-song wrote:

> @ayermolo is correct about what I meant.
> 
> It's an interesting case, and other consumers may well want to know about it. Exploring this with a vendor-specific implementation is the correct way forward. If it turns out to be genuinely useful, it would be worth proposing as a new feature in DWARF v6.
> 
> Right now, though, my question is basically, how much size increase do we see in the DWARF with this new feature? If it's very small (maybe the optimization does not fire very often), then there's not much harm in emitting the info all the time, as the patch currently implements it. If there's a noticeable increase, though, that's a concern for some vendors and we might want to limit the situations where the info is emitted.

The following are some statistics when building a linux kernel with and without this patch:
```
without change:
Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  ...
  [49] .debug_aranges    PROGBITS        0000000000000000 68a5000 000680 00      0   0  1
  [50] .debug_info       PROGBITS        0000000000000000 68a5680 b61ff8d 00      0   0  1
  [51] .debug_abbrev     PROGBITS        0000000000000000 11ec560d 4a606a 00      0   0  1
  [52] .debug_line       PROGBITS        0000000000000000 1236b677 1cc7dc3 00      0   0  1
  [53] .debug_frame      PROGBITS        0000000000000000 14033440 45dcd8 00      0   0  8
  [54] .debug_str        PROGBITS        0000000000000000 14491118 5bd10f 01  MS  0   0  1
  [55] .debug_addr       PROGBITS        0000000000000000 14a4e227 5e2710 00      0   0  1
  [56] .debug_line_str   PROGBITS        0000000000000000 15030937 0534fe 01  MS  0   0  1
  [57] .debug_loclists   PROGBITS        0000000000000000 15083e35 18f1a7c 00      0   0  1
  [58] .debug_rnglists   PROGBITS        0000000000000000 169758b1 3aaec7 00      0   0  1
  [59] .debug_str_offsets PROGBITS       0000000000000000 16d20778 284c478 00      0   0  1

with change:
Section Headers:                                                                         
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  ...
  [49] .debug_aranges    PROGBITS        0000000000000000 68a5000 000680 00      0   0  1
  [50] .debug_info       PROGBITS        0000000000000000 68a5680 b6207e5 00      0   0  1
  [51] .debug_abbrev     PROGBITS        0000000000000000 11ec5e65 4a72f2 00      0   0  1
  [52] .debug_line       PROGBITS        0000000000000000 1236d157 1cc7dc3 00      0   0  1
  [53] .debug_frame      PROGBITS        0000000000000000 14034f20 45dcd8 00      0   0  8
  [54] .debug_str        PROGBITS        0000000000000000 14492bf8 5bd10f 01  MS  0   0  1
  [55] .debug_addr       PROGBITS        0000000000000000 14a4fd07 5e2710 00      0   0  1
  [56] .debug_line_str   PROGBITS        0000000000000000 15032417 0534fe 01  MS  0   0  1
  [57] .debug_loclists   PROGBITS        0000000000000000 15085915 18f1a7c 00      0   0  1
  [58] .debug_rnglists   PROGBITS        0000000000000000 16977391 3aaec7 00      0   0  1
  [59] .debug_str_offsets PROGBITS       0000000000000000 16d22258 284c478 00      0   0  1
```

For debug_info section, without this patch the size is 0xb61ff8d and with this patch the size is 0xb6207e5. So the increase is 0x858 which is tiny.  


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