Okay, I ran a little experiment - here's the size of the debug sections that Fission would keep (for base library):

  .debug_abbrev:          8932 - 0.06%
  .debug_line:          374134 - 2.6%
  .debug_frame:         671200 - 4.5%

Not that much. On the other hand, .debug_info is a significant contributor:

  .debug_info(full):   4527391 - 30%

Here's what this contains: All procs get a corresponding DWARF entry, and we declare all Cmm blocks as "lexical blocks". The latter isn't actually required right now - to my knowledge, GDB simply ignores it, while LLDB shows it as "inlined" routines. In either case, it just shows yet more GHC-generated names, so it's really only useful for profiling tools that know Cmm block names.

So here's what we get if we strip out block information:

  .debug_info(!block): 1688410 - 11%

This eliminates a good chunk of information, and might therefore be a good idea for "-g1" at minimum. If we want this as default for 7.10, this would make the total overhead about 18%. Acceptable? I can supply a patch if needed.

Just for comparison - for Fission we'd strip proc records as well, which would cause even more extreme savings:

  .debug_info(!proc):    36081 - 0.2%

At this point the overhead would be just about 7% - but without doing Fission properly this would most certainly affect debuggers.

Greetings,
  Peter

On 03/01/2015 21:22, Johan Tibell wrote:
> How much debug info (as a percentage) do we currently generate? Could we just keep it in there in the release?

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