[clang] [llvm] [clang][DebugInfo] Emit unified (Itanium) mangled name to structor declarations (PR #154142)

[Michael Buch via llvm-commits]

Michael137 wrote:

Here is the debug-info increase when I run bloaty on all the Clang/LLDB/LLVM object files:
```
$ bloaty `find builds-lldb/with-patch/ -name '*.o'` -- `find builds-lldb/no-patch/ -name '*.o'`
    FILE SIZE        VM SIZE    
 --------------  -------------- 
   +15%  +207Mi  [ = ]       0    .debug_str
  +9.6% +56.2Mi  [ = ]       0    .rela.debug_str_offsets
  +9.6% +9.37Mi  [ = ]       0    .debug_str_offsets
  +0.7% +4.29Mi  [ = ]       0    .debug_info
  +0.0%    +404  [ = ]       0    .group
  +0.0%    +230  +0.0%    +210    .rodata.str1.1
  +0.0%     +12  [ = ]       0    .debug_addr
  +0.1%      +8  [ = ]       0    .data.rel.ro._ZTVN4llvm2cl15OptionValueCopyIbEE
  +1.7%      +8  [ = ]       0    .data.rel.ro._ZTVN5clang4Sema27ContextualImplicitConverterE
  +150%      +6  [ = ]       0    .rodata._ZSt14in_place_indexILm10EE
 -66.7%      -2  [ = ]       0    .rodata._ZN4llvm7IsaPredIJN5clang17OpenACCBindClauseEEEE
  -0.9%      -4  [ = ]       0    .rodata._ZN4llvm14GlobalVariable11AllocMarkerE
  -1.3%      -6  [ = ]       0    .rodata._ZSt14in_place_indexILm0EE
  -3.0%     -12  [ = ]       0    .rodata._ZN4llvm3LLT28PointerAddressSpaceFieldInfoE
  -0.8%     -42  [ = ]       0    .rodata._ZSt7nullopt
  -0.0%    -191  [ = ]       0    .comment
  -0.1% -17.8Ki  [ = ]       0    .debug_line_str
  -1.9%  -243Ki  [ = ]       0    .debug_abbrev
  +4.9%  +277Mi  +0.0%    +210    TOTAL
```

Google used an earlier version of this patch to check how their binaries are affected. The `.debug_str` section exceeds the 4GB limit for some of the larger binaries. So I added a command-line option to switch this behaviour off. @cmtice @labath does that alleviate some of your concerns?

Also CCing @jmorse as a heads up for Sony in case you have any concerns.

https://github.com/llvm/llvm-project/pull/154142