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# Cost Calculation on Loop Invariant on Arithmetic operations on RTL

• From: Ajit Kumar Agarwal <ajit dot kumar dot agarwal at xilinx dot com>
• To: "vmakarov at redhat dot com" <vmakarov at redhat dot com>, Richard Biener <richard dot guenther at gmail dot com>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
• Cc: 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: Tue, 17 Feb 2015 08:45:02 +0000
• Subject: Cost Calculation on Loop Invariant on Arithmetic operations on RTL
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```Hello All:

I can see the Loop invariant pass in the GCC on RTL considering the register pressure and the cost manipulation
With respect to SET destination node in RTL.

The Loop invariant takes care of only address arithmetic candidates of Loop invariance.

In the function get_inv_cost, I can see the following check for the updation of comp_cost and the comp_cost
Gets incremented with respect all the dependence on the def node of the invariant variable.

(*comp_cost += inv->cost + inv->eqno

Is there any specific reasons of addr_uses  less than the actual uses check for the address arithmetic candidate
Of Loop invariant. I think we should be aggressive enough and can do the cost calculation without this check.

One more point the above cost calculation should not be considering the register pressure_costs.