/// <summary>
/// The last Rule is often a 'fallback' rule with an empty condition. If this is the case,
/// we can sometimes perform an optimisation that reduces the overall code size.
/// </summary>
/// <returns>Root of the generated tree.</returns>
private Node?BuildFallbackSequence()
{
// sanity check
if (ruleSet.NumRules <= 1)
{
return(null);
}
// check that there is a fallback rule
RuleSetEntry lastRule = ruleSet[ruleSet.NumRules - 1];
if (!lastRule.EffectiveCondition.IsEmpty)
{
return(null);
}
// check that sequence nodes are permitted
if (!spec.Config.AllowSequence)
{
return(null);
}
if (spec.Config.Verbose)
{
Console.WriteLine("Performing fallback sequence optimisation.");
}
// remove the fallback rule and build the tree
RuleSet rSet = ruleSet.DeriveExcludingLast();
var builder = new TreeBuilder(spec, rSet, this);
Node node = builder.Build();
// ensure that there is a sequence node including the root
// of the tree
SequenceNode seq;
if (node is SequenceNode)
{
seq = (SequenceNode)node;
}
else
{
seq = new SequenceNode(spec);
seq.Append(node);
}
// now paste the fallback rule onto the end of the sequence
seq.Append(lastRule.Rule);
return(seq);
}
/// <summary>
/// Generate an if-else node for a Rule.
/// </summary>
private Node CreateIfElseNode(RuleSetEntry entry, Node elseBranch)
{
// generate a child node for the rule
if (entry.EffectiveCondition.IsEmpty)
{
if (spec.Config.Verbose && !(elseBranch is EmptyNode))
{
Console.WriteLine("Discarding non-empty else branch; condition is empty.");
}
return(entry.Rule);
}
else
{
if (spec.Config.NoOptimiseIfConditionNodes)
{
return(new IfElseNode(spec, entry.Rule.Condition, entry.Rule, elseBranch));
}
else
{
return(new IfElseNode(spec, entry.EffectiveCondition, entry.Rule, elseBranch));
}
}
}