public static Dictionary <Expression, (int usageCount, int cost)> Evaluate(Expression expression)
{
var c = new ExpressionCounter();
c.Visit(expression);
return(c.Expressions);
}
public static Expression EliminateCommonSubexpressions(this Expression expression, ref IEnumerable <ParameterExpression> variablePool)
{
var pool = new VariablePool(variablePool);
do
{
var q = from e in ExpressionCounter.Evaluate(expression)
where e.Value.usageCount > 1 && e.Value.cost > 0
orderby e.Value.usageCount descending, e.Value.cost descending
select e.Key;
var mostExpensive = q.FirstOrDefault();
if (mostExpensive == null)
{
break;
}
// introduce a variable for mostExpensive
var t = pool.GetVariable(mostExpensive.Type);
// TODO: fix the order of the variables. Assignments should go after all depends
expression = MergeBlocks(t, mostExpensive, ExpressionReplacer.Replace(expression, mostExpensive, t, new CodeComparer()));
} while (true);
variablePool = pool.Variables;
return(expression);
}
