[PATCH] D74169: [WIP][LLD][ELF][DebugInfo] Remove obsolete debug info.

[David Blaikie via Phabricator via llvm-commits]

dblaikie added a comment.

In D74169#1974097 <https://reviews.llvm.org/D74169#1974097>, @avl wrote:

> > Might be worth comparing with -gdb-index too (though not sure if gdb-index will be immediately compatible with the DWARF aware linking, so a difficult comparison - but even comparing "gdb-index without DWARF-aware linking V DWARF-aware linking without gdb-index", etc)
>
> here are the results for clang binary:
>
>   -------------------------------------------------------------
>   |     Options    | Run-time, sec | Used Memory, kb |  Size  |
>   -------------------------------------------------------------
>   |                |     35.58     |     9403596     |  1,4G  |
>   -------------------------------------------------------------
>   |  gc-debuginfo  |    109.15     |    14275444     |  783M  |
>   -------------------------------------------------------------
>   |  gc-debuginfo  |    130.63     |    14394700     |  797M  |
>   |   gdb-index    |               |                 |        |
>   -------------------------------------------------------------
>   |   gdb-index    |     52.88     |     9524976     |  1.5G  | 
>   -------------------------------------------------------------
>


Ah, sorry, I meant specifically related to the gdb startup time point you made earlier about DWARF-aware linking improving startup time. It'd be useful to measure startup time with a gdb-index for comparison. (I'm guessing the time in the above chart is linking time, rather than GDB startup time)

> I did not check whether gdb-index is compatible with DWARF aware linking output.
> 
> There probably exists the room for optimization of gdb-index(related to the strategy of DWARF context creation). 
>  As it was mentioned in  https://reviews.llvm.org/D74773#1920751 simple caching of DWARF context results in an 8% performance increase and 20% memory usage increase. 
>  It is probably worth implementing some smart strategy(reference counting?) that will keep DWARF context while there are users of it and release it when it is not expected to be used(so that it does not hold all DWARF contexts forever).




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