Awareness of register pressure on strength reduction of induction variables.

[Richard Biener]

On Tue, Sep 1, 2015 at 7:57 PM, Ajit Kumar Agarwal
<ajit.kumar.agarwal@xilinx.com> wrote:
> All;
>
> The Global code motion are the important optimization that have an impact on register spills and Fetch. Thus
> The Global code motion takes into account the increase or decrease of register pressure.
>
> Strength Reductions is an important optimization that has an impact on register pressure. The strength reduction
> Optimizations doesn't take into account the register pressure and especially the strength reduction for induction
> Variables that are inside the Loops. Loops are the bottleneck for the register pressure and any spill inside the loops
> Based on strength reduction of induction variables degrades the performance of the Loops.
>
> Thus the strength reductions in general and especially the strength reduction for induction variables should take
> Into account the register pressure based on Live range info.
>
> I don't think we do take into account the register pressure for strength reduction optimization in general and especially the
> Strength reduction based on induction variables.

We do loop strength reduction as part of induction variable
optimization and I am not aware that IVO takes
existing register pressure into account (it does limit the number of
IVs it creates IIRC).

Richard.

> Thanks & Regards
> Ajit