ivopts improvement

[Tom de Vries]

Hi Paolo,

On 03/03/2011 09:44 AM, Paolo Bonzini wrote:
> On 03/02/2011 11:01 PM, Tom de Vries wrote:
>> +  if (TREE_CODE (nit) == COND_EXPR)
>> +    {
>> +      if (!loop_only_exit_p (loop, exit))
>> +        return false;
>> +
>> +      return iv_elimination_compare_lt (use, cand, bound, nit, comp);
>> +    }
>> +
> 
> You probably need a comment on top of iv_elimination_compare_lt, 
> otherwise I'm left wondering why this isn't
> 
>    if (TREE_CODE (nit) == COND_EXPR
>        && loop_only_exit_p (loop, exit)
>        && iv_elimination_compare_lt (use, cand, bound, nit, comp))
>      return true;
> 

You're right, there's a comment missing. I added it now.

> Also, the check on nit is an optimization.  

It's not, hopefully now explained by the comment.

> Perhaps you should add a 
> gcc_checking_assert to i_elimination_compare_lt and/or remove this from 
> get_lt_bound:
> 
>> +  if (TREE_CODE (nit) != COND_EXPR)
>> +    return NULL_TREE;
>> +

It's duplicate test, so I turned it into a gcc_checking_assert.

> Or perhaps loop_only_exit_p could be optimized by computing it ahead of 
> time, possibly at the same time as loop_body_includes_call.  This way it 
> becomes very cheap and the code above can just call 
> iv_elimination_compare_lt without any pre-screening.

Gave it a try in a new patch.

reg-tested on x86_64. Better?

Thanks,
- Tom
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