On 11/26/13 03:52, Bin.Cheng wrote:
On Tue, Nov 26, 2013 at 6:06 AM, Jeff Law <l...@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
