[gomp4, committed] Add counter inits to zero_iter_bb in expand_omp_for_init_counts

[Tom de Vries <Tom_deVries@mentor.com>]

[ was: Re: [patch] Add counter inits to zero_iter_bb in 
expand_omp_for_init_counts ]

On 01/10/15 15:37, Tom de Vries wrote:
> On 01/10/15 14:49, Jakub Jelinek wrote:
>> On Thu, Oct 01, 2015 at 02:46:01PM +0200, Tom de Vries wrote:
>>> this patch adds initialization in zero_iter_bb of counters introduced in
>>> expand_omp_for_init_counts.
>>>
>>> This removes the need to set TREE_NO_WARNING on those counters.
>>
>> Why do you think it is a good idea?
>
> In replace_ssa_name, I've recently added the assert:
> ...
>            gcc_assert (!SSA_NAME_IS_DEFAULT_DEF (name));
> ...
>
> On the gomp-4_0-branch, this assert triggers for a collapsed acc loop,
> which uses expand_omp_for_generic for omp-expansion.  The assert
> triggers because (some of) the counters added by
> expand_omp_for_init_counts are not initialized on all paths.
>
> On trunk, for the test-case in the patch, this assert doesn't trigger
> because the omp function is split off before ssa.
>
>> I'd be afraid it slows things down unnecessarily.
>
> I think zero_iter_bb is a block that is expected not to be executed
> frequently.
>
> I've attached an sdiff of x86_64 assembly for the test-case (before
> left, after right). AFAICT, this patch has the effect that it speeds up
> the frequent path with one instruction.
>
>>  Furthermore, I'd prefer not to change this area of code before
>> gomp-4_1-branch is merged, as it will be a nightmare for the merge
>> otherwise.
>
> Committing to gomp-4_0-branch for now would work for me.
>

Committed to gomp-4_0-branch.

Thanks,
- Tom