[libcxx-commits] [libcxx] [libc++] Encode additional ODR-affecting properties in the ABI tag (PR #69669)

[Louis Dionne via libcxx-commits]

ldionne wrote:

Here's the results for `libcxx/test/std/algorithms/alg.modifying.operations/alg.transform/ranges.transform.binary.range.pass.cpp` when compiling with `-O0 -g` (that's what you wanted right?):

```
$ bloaty debug-before.o
    FILE SIZE        VM SIZE
 --------------  --------------
  30.9%  5.60Mi  44.0%  5.60Mi    ,__debug_str
  20.5%  3.72Mi   0.0%       0    String Table
  14.7%  2.67Mi  21.0%  2.67Mi    ,__debug_info
  14.1%  2.56Mi  20.1%  2.56Mi    ,__text
   7.6%  1.38Mi   0.0%       0    [Unmapped]
   4.7%   870Ki   6.7%   870Ki    ,__debug_line
   2.8%   524Ki   4.0%   524Ki    ,__apple_names
   2.5%   458Ki   3.5%   458Ki    ,__compact_unwind
   1.6%   288Ki   0.0%       0    Symbol Table
   0.2%  40.3Ki   0.3%  40.3Ki    ,__const
   0.2%  33.7Ki   0.3%  33.7Ki    ,__apple_types
   0.1%  10.7Ki   0.1%  10.7Ki    ,__literal16
   0.0%  6.80Ki   0.1%  6.80Ki    ,__data
   0.0%  2.68Ki   0.0%  2.68Ki    ,__literal4
   0.0%  1.63Ki   0.0%       0    [Mach-O Headers]
   0.0%  1.45Ki   0.0%  1.45Ki    ,__debug_abbrev
   0.0%     664   0.0%     664    ,__cstring
   0.0%     372   0.0%     372    ,__apple_namespac
   0.0%      56   0.0%      56    ,__eh_frame
   0.0%      52   0.0%      52    [2 Others]
   0.0%      48   0.0%      48    ,__debug_ranges
 100.0%  18.1Mi 100.0%  12.7Mi    TOTAL

$ bloaty debug-after.o
    FILE SIZE        VM SIZE
 --------------  --------------
  30.9%  5.61Mi  44.0%  5.61Mi    ,__debug_str
  20.6%  3.73Mi   0.0%       0    String Table
  14.7%  2.67Mi  21.0%  2.67Mi    ,__debug_info
  14.1%  2.56Mi  20.1%  2.56Mi    ,__text
   7.6%  1.38Mi   0.0%       0    [Unmapped]
   4.7%   870Ki   6.7%   870Ki    ,__debug_line
   2.8%   524Ki   4.0%   524Ki    ,__apple_names
   2.5%   458Ki   3.5%   458Ki    ,__compact_unwind
   1.6%   288Ki   0.0%       0    Symbol Table
   0.2%  40.3Ki   0.3%  40.3Ki    ,__const
   0.2%  33.7Ki   0.3%  33.7Ki    ,__apple_types
   0.1%  10.7Ki   0.1%  10.7Ki    ,__literal16
   0.0%  6.80Ki   0.1%  6.80Ki    ,__data
   0.0%  2.68Ki   0.0%  2.68Ki    ,__literal4
   0.0%  1.63Ki   0.0%       0    [Mach-O Headers]
   0.0%  1.45Ki   0.0%  1.45Ki    ,__debug_abbrev
   0.0%     664   0.0%     664    ,__cstring
   0.0%     372   0.0%     372    ,__apple_namespac
   0.0%      56   0.0%      56    ,__eh_frame
   0.0%      52   0.0%      52    [2 Others]
   0.0%      48   0.0%      48    ,__debug_ranges
 100.0%  18.1Mi 100.0%  12.7Mi    TOTAL
```

There doesn't seem to be a super significant change here either. Also FWIW I have no idea how symbols are stored inside debug information and whether it's possible to change that without breaking the world, but it would be quite awesome if they were stored in some sort of compressed form. For example we could store symbols in some kind of prefix tree and then this change would have basically no effect on the overall size of symbols.

https://github.com/llvm/llvm-project/pull/69669