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Re: Awareness of register pressure on strength reduction of induction variables.
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Ajit Kumar Agarwal <ajit dot kumar dot agarwal at xilinx dot com>
- Cc: Jeff Law <law at redhat dot com>, "vmakarov at redhat dot com" <vmakarov at redhat dot com>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, Vinod Kathail <vinodk at xilinx dot com>, Shail Aditya Gupta <shailadi at xilinx dot com>, Vidhumouli Hunsigida <vidhum at xilinx dot com>, Nagaraju Mekala <nmekala at xilinx dot com>
- Date: Wed, 2 Sep 2015 14:52:30 +0200
- Subject: Re: Awareness of register pressure on strength reduction of induction variables.
- Authentication-results: sourceware.org; auth=none
- References: <37378DC5BCD0EE48BA4B082E0B55DFAA429746F6 at XAP-PVEXMBX02 dot xlnx dot xilinx dot com>
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