[RFC] libgcov.c re-factoring and offline profile-tool

Rong Xu xur@google.com
Wed Jan 8 22:20:00 GMT 2014

On Wed, Dec 18, 2013 at 9:28 AM, Xinliang David Li <davidxl@google.com> wrote:
>>>  #ifdef L_gcov_merge_ior
>>>  /* The profile merging function that just adds the counters.  It is given
>>> -   an array COUNTERS of N_COUNTERS old counters and it reads the same number
>>> -   of counters from the gcov file.  */
>>> +   an array COUNTERS of N_COUNTERS old counters.
>>> +   When SRC==NULL, it reads the same number of counters from the gcov file.
>>> +   Otherwise, it reads from SRC array.  */
>>>  void
>>> -__gcov_merge_ior (gcov_type *counters, unsigned n_counters)
>>> +__gcov_merge_ior (gcov_type *counters, unsigned n_counters,
>>> +                  gcov_type *src, unsigned w __attribute__ ((unused)))
>> So the new in-memory variants are introduced for merging tool, while libgcc use gcov_read_counter
>> interface?
>> Perhaps we can actually just duplicate the functions to avoid runtime to do all the scalling
>> and in_mem tests it won't need?
> I thought about this one a little. How about making the interface
> change conditionally, but still share the implementation?  The merge
> function bodies mostly remain unchanged and there is no runtime
> penalty for libgcov.  The new macros can be shared across most of the
> mergers.
> #define GCOV_MERGE_EXTRA_ARGS  gcov_type *src, unsigned w
> #define GCOV_READ_COUNTER  *(src++) * w
> #else
> #define GCOV_READ_COUNTER gcov_read_counter ()
> #endif
> __gcov_merge_add (gcov_type *counters, unsigned n_counters,
>                                   GCOV_MERGE_EXTRA_ARGS)
> {
>  for (; n_counters; counters++, n_counters--)
>   {
>       *counters += GCOV_READ_COUNTER ;
>    }
> }
> thanks,

Personally I don't think the run time test of in_mem will cause any
issue. This is in profile dumping, why don't we care a few more cycle
heres? it won't pollute the profile.

If you really don't like that, we can use the above approach, or I can
hide the logic in gcov_read_counter(), i.e. overload
gcov_read_counter() in profile_tool. For that, I will need a new
global variable SRC and set it before calling the merge function.
I would prefer to keep weight in _gcov_merge_* argument list.

What do you think?


> David
>> I would suggest going with libgcov.h changes and clenaups first, with interface changes next
>> and the gcov-tool is probably quite obvious at the end?
>> Do you think you can split the patch this way?
>> Thanks and sorry for taking long to review. I should have more time again now.
>> Honza

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