[Ping]Two pending IVOPT patches

[Jeff Law]

On 11/26/13 03:52, Bin.Cheng wrote:
> On Tue, Nov 26, 2013 at 6:06 AM, Jeff Law <law@redhat.com> wrote:
>> On 11/25/13 02:11, Bin.Cheng wrote:
>>>
>>>
>>> Slightly tune to make iv cand choosing algorithm more accurate:
>>> http://gcc.gnu.org/ml/gcc-patches/2013-11/msg01574.html
>>
>> It would help if you had some sample codes where this patch was useful.  I
>> can kind-of see what's going on, but I'm way too unfamiliar with the tree-IV
>> code to review this change.
>>
> Jeff, Thanks to your review.
> As for example, consider below code on ARM/cortex-m4, (the code itself
> may be non-sense):
[ ... ]
So in this testcase, it looks like the effect is to eliminate the IVs 
for the loop counters, instead expressing the loop termination in terms 
of the pointers.

As far as I can tell this is entirely due to the changes to iv_ca_narrow.

Do you have any codes where iv_ca_extend helps?  I can see how that hunk 
appears to be safe, and I'm guessing that setting the cost pair at each 
step could potentially give more accurate costing on the next iteration 
of the loop.   But I'd love to be able to see this effect directly 
rather than just assuming it's helpful.  Given that I'm prepared to 
approve the iv_ca_extend hunk.

I realize the changes to iv_ca_extend are of lesser importance, but I'm 
still working my way through the tree IV code to get some basic 
understanding of what it's doing and why.  I hope to be able to look at 
iv_ca_narrow in more detail over the weekend.

jeff