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

[Xinliang David Li <davidxl at google dot com>]

On Wed, Jan 8, 2014 at 2:20 PM, Rong Xu <xur@google.com> wrote:
> 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.
>>
>> #ifdef IN_PREOFILE_TOOL
>> #define GCOV_MERGE_EXTRA_ARGS  gcov_type *src, unsigned w
>> #define GCOV_READ_COUNTER  *(src++) * w
>> #else
>> #define GCOV_MERGE_EXTRA_ARGS
>> #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?

or perhaps just define an inline wrapper function to read counter.
This wrapper function takes src as input. if src is NULL, call
gcov_read_counter.

David

>
> -Rong
>
>>
>> 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