[LLVMdev] -gcolumn-info and PR 14106

Eric Christopher
Thu, 26 Jun 2014 19:31:02 -0000

On Thu, Jun 26, 2014 at 9:46 AM, Diego Novillo <dnovillo at google.com>
wrote:
> For -Rpass, and other related uses, I am looking at enabling column info by
> default. David pointed me at PR 14106, which seems to be the original
> motivation for introducing -gcolumn-info. However, I am finding no
> differences when using it on this test.  I've tried building
with/without
> -gcolumn-info and found almost no difference in compile time (+0.4%):
>
> $ /usr/bin/time clang -w -fno-builtin -O2 -g -gcolumn-info test-tgmath2.i
> 474.38user 2.10system 7:58.00elapsed 99%CPU
>
> $ /usr/bin/time clang -w -fno-builtin -O2 -g  test-tgmath2.i
> 472.63user 2.02system 7:56.11elapsed 99%CPU
>
> I'm running clang from trunk @211693.
>
> The size of all debug sections (according to readelf) are:
>
> - with -g -gcolumn-info: 836,177 bytes
> - with -g: 826,552 bytes
>
> That's a growth of about 1% in debug info size.
>
> These numbers are in line with a comparative build I did of our internal
> codebase. The build included a massive number of C and C++ files. For C
> files, total file size grows by 1% on average. For C++ files the average
> growth is around 0.2%. Build times are unchanged as well.
>
> Does anyone remember any other edge case I may want to try? It seems to me
> that these differences are not really worth the effort of having a flag
> controlling column information.
>

I remember it being larger last I'd looked, but I know I didn't have
quite the range that you just tested. I'm all for turning it on -
especially if it doesn't really cost us anything.

Adrian: any issues on your end before I turn it on by default and
remove the option? This will also obviate a few of the patches that
you had to distinguish call sites as well I think.

-eric