Re: [PATCH v3 1/1] Don't rewind PC for GHC generated frames

[Bartosz Nitka <niteria at gmail dot com>]

Hi Simon,

Thanks for taking a look at the updated version.

> I hoped there would be some comments from others.

Is there anyone we could ask directly?

> In particular, is anybody
> able to tell if adding a call to find_pc_compunit_symtab in
> get_frame_address_in_block is a performance concern?  How frequently is
> get_frame_address_in_block called, and how costly is find_pc_compunit_symtab
> to call?

This is a valid concern.
When I originally made this change, I was focusing on making dwarf2_frame_cache
work. dwarf2_frame_cache calls get_frame_address_in_block and then calls
dwarf2_frame_find_quirks. dwarf2_frame_find_quirks calls
find_pc_compunit_symtab.
That makes me think that for this code path there should be no difference.

That's only one code path, I haven't analyzed others. If performance
turned out to be a
problem, then undoing the effect of get_frame_address_in_block in
dwarf2_frame_cache
would get me 90% of what I care about currently (unwinding).

That said, there must be a way to resolve this in a data driven way.
Are there any pre-existing benchmarks I can run?
Is there a scenario that I can benchmark to resolve the questions above?

> However, please tell me if you are fine with
> my suggestion below.

Yes, that's a good change. Thanks! If it helps move things along I'm
happy to submit
an updated version.

Thanks,
Bartosz