Re: [google gcc-4_8] Don't use gcov counter related ssa name as induction variables

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

ok for google branch for now.  Please resubmit to trunk and backport
the trunk version if needed.

thanks,

David

On Tue, Feb 11, 2014 at 10:29 AM, Wei Mi <wmi@google.com> wrote:
>>> +/* Return true if the use is defined by a gcov counter var.
>>> +   It is used to check if an iv candidate is generated for
>>> +   profiling. For profile generated ssa name, we should not
>>> +   use it as IV because gcov counter may have data-race for
>>> +   multithread program, it could involve tricky bug to use
>>> +   such ssa var in IVOPT.
>>> +
>>
>> Add the snippets describing how ralloc introduces a second gcov
>> counter load and asynchronous update of it from another thread leading
>> to bogus trip count.
>>
>> Also mention that setting volatile flag on gcov counter accesses may
>> greatly degrade profile-gen performance.
>>
>
> Comments added.
>
>>> +  if (!is_gimple_assign (stmt))
>>> +    return false;
>>> +
>>> +  rhs = gimple_assign_rhs1 (stmt);
>>> +  if (TREE_CODE (rhs) != ARRAY_REF)
>>> +    return false;
>>> +
>>> +  decl = TREE_OPERAND (rhs, 0);
>>> +  if (TREE_CODE (decl) != VAR_DECL)
>>> +    return false;
>>
>>
>>
>> Also check TREE_STATIC and DECL_ARTIFICIAL flag.
>>
>>
>> David
>>
>
> Check added. Add DECL_ARTIFICIAL setting in build_var() in coverage.c.
>
> The updated patch is attached.
>
> Thanks,
> Wei.