On Tue, May 15, 2012 at 7:05 AM, Jiangning Liu <jiangning....@arm.com> wrote: > Hi, > > Why can't we replace function force_expr_to_var_cost directly with function > computation_cost in tree-ssa-loop-ivopt.c? > > Actually I think it is inaccurate for the current recursive algorithm in > force_expr_to_var_cost to estimate expr cost. Instead computation_cost can > count some back-end factors and make the estimation more accurate. > > For example, using computation_cost, we may check whether back-ends can tie > some modes transformation expressed by SUBREG or not. If we use > force_expr_to_var_cost, some more computations around type > promotion/demotion would increase the cost estimated. > > Looking at the algorithm in force_expr_to_var_cost, it is just to analyze > the operator in the expression and give estimation. Should it be the same as > expanding EXPR to RTX and give estimation like in computation_cost? > > Any thoughts?
I suppose Zdenek may remember. Richard. > Thanks, > -Jiangning > > >
