[clang] [llvm] [clang][DebugInfo] Add symbol for debugger with VTable information. (PR #130255)

[Carlos Alberto Enciso via cfe-commits]

CarlosAlbertoEnciso wrote:

@dwblaikie I have used bloaty to get some debug info size changes.

The VTable work is based on this specific revision c02019141.

I built Clang using `DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_PROJECTS=clang`:
- at that specific revision c02019141 (original Clang)  --> **original**.
- and that revision with the current patch applied --> **modified**.

Using those builds I built Clang twice with debug info, using `DCMAKE_BUILD_TYPE=Debug -DLLVM_ENABLE_PROJECTS=clang`:
Using **original** --> **reference**
Using **modified** --> **vtables**

These are the sizes reported by `bloaty`
```
$ [...]./bloaty [...]/vtables/bin/clang++ -- [...]/reference/bin/clang++
    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.2%  +436Ki  [ = ]       0    .debug_str
  +0.1%  +361Ki  [ = ]       0    .debug_info
  +3.2%  +300Ki  [ = ]       0    .debug_abbrev
  +0.3%  +122Ki  [ = ]       0    .debug_addr
  +0.1% +69.9Ki  [ = ]       0    .debug_str_offsets
  +0.0% +9.75Ki  [ = ]       0    .debug_line
  +0.0% +2.51Ki  [ = ]       0    .debug_rnglists
  +0.0%     +21  [ = ]       0    .debug_line_str
  +9.9%     +15  [ = ]       0    .comment
  +0.0%      +1  [ = ]       0    .debug_loclists
  +0.1% +1.27Mi  [ = ]       0    TOTAL

$ ls -Ll [...]/vtables/bin/clang++ [...]/reference/bin/clang++
-rwxrwxr-x 1 [...] 1678577192 May 20 10:53 [...]/vtables/bin/clang++
-rwxrwxr-x 1 [...] 1677243032 May 20 10:35 [...]/reference/bin/clang++
```
```
$ [...]./bloaty [...]/vtables/bin/llc -- [...]/reference/bin/llc
    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.2%  +291Ki  [ = ]       0    .debug_str
  +0.1%  +283Ki  [ = ]       0    .debug_info
  +3.0%  +202Ki  [ = ]       0    .debug_abbrev
  +0.3% +71.1Ki  [ = ]       0    .debug_addr
  +0.1% +42.0Ki  [ = ]       0    .debug_str_offsets
  +0.0% +1.94Ki  [ = ]       0    .debug_rnglists
  +0.0%    +486  [ = ]       0    .debug_line
  +0.0%     +18  [ = ]       0    .debug_line_str
  +9.9%     +15  [ = ]       0    .comment
  +0.0%      +1  [ = ]       0    .debug_loclists
  +0.1%  +892Ki  [ = ]       0    TOTAL
```
```
$ [...]./bloaty [...]/vtables/bin/opt -- [...]/reference/bin/opt

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.2%  +293Ki  [ = ]       0    .debug_str
  +0.1%  +283Ki  [ = ]       0    .debug_info
  +3.0%  +202Ki  [ = ]       0    .debug_abbrev
  +0.3% +71.3Ki  [ = ]       0    .debug_addr
  +0.1% +42.1Ki  [ = ]       0    .debug_str_offsets
  +0.0% +1.93Ki  [ = ]       0    .debug_rnglists
  +0.0%    +486  [ = ]       0    .debug_line
  +0.0%     +18  [ = ]       0    .debug_line_str
  +9.9%     +15  [ = ]       0    .comment
  +0.0%      +1  [ = ]       0    .debug_loclists
  +0.1%  +895Ki  [ = ]       0    TOTAL
```
```
$ [...]./bloaty [...]/vtables/bin/llvm-as -- [...]/reference/bin/llvm-as
    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.1% +59.6Ki  [ = ]       0    .debug_info
  +0.1% +34.6Ki  [ = ]       0    .debug_str
  +2.7% +29.9Ki  [ = ]       0    .debug_abbrev
  +0.3% +11.2Ki  [ = ]       0    .debug_addr
  +0.1% +6.51Ki  [ = ]       0    .debug_str_offsets
  +0.0%    +288  [ = ]       0    .debug_rnglists
  +0.0%     +18  [ = ]       0    .debug_line_str
  +9.9%     +15  [ = ]       0    .comment
  -0.0%     -22  [ = ]       0    .debug_line
  +0.1%  +142Ki  [ = ]       0    TOTAL
```


https://github.com/llvm/llvm-project/pull/130255