Live on Exit renaming.

[Bin.Cheng]

On Mon, Jul 6, 2015 at 6:02 AM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
> On Sat, Jul 4, 2015 at 3:45 PM, Ajit Kumar Agarwal wrote:
>> I am not sure why the above optimization is not implemented in GCC.
>
> -fsplit-ivs-in-unroller

And thing might have changed.  Given the condition GCC does IVO on
gimple, unrolling on RTL, there is inconsistency between the two
optimizer since IVO takes register pressure of IVs into consideration
and assumes IVs will take single registers.  At least for some cases,
splitting live range of IVs results in bad code.  See PR29256 for more
information.  As described in the comment, actually I am going to do
some experiments disabling such transformation to see what happens.

Thanks,
bin
>
> Ciao!
> Steven