private void LowerDecisionTree(DecisionTree.ByType byType)
{
var inputConstant = byType.Expression.ConstantValue;
if (inputConstant != null)
{
if (inputConstant.IsNull)
{
// input is the constant null
LowerDecisionTree(byType.Expression, byType.WhenNull);
if (byType.WhenNull?.MatchIsComplete != true)
{
LowerDecisionTree(byType.Expression, byType.Default);
}
}
else
{
// input is a non-null constant
foreach (var kvp in byType.TypeAndDecision)
{
LowerDecisionTree(byType.Expression, kvp.Value);
if (kvp.Value.MatchIsComplete)
{
return;
}
}
LowerDecisionTree(byType.Expression, byType.Default);
}
}
else
{
var defaultLabel = _factory.GenerateLabel("byTypeDefault");
// input is not a constant
if (byType.Type.CanContainNull())
{
// first test for null
var notNullLabel = _factory.GenerateLabel("notNull");
var inputExpression = byType.Expression;
var objectType = _factory.SpecialType(SpecialType.System_Object);
var nullValue = _factory.Null(objectType);
BoundExpression notNull = byType.Type.IsNullableType()
? _localRewriter.RewriteNullableNullEquality(_factory.Syntax, BinaryOperatorKind.NullableNullNotEqual, byType.Expression, nullValue, _factory.SpecialType(SpecialType.System_Boolean))
: _factory.ObjectNotEqual(nullValue, _factory.Convert(objectType, byType.Expression));
_loweredDecisionTree.Add(_factory.ConditionalGoto(notNull, notNullLabel, true));
LowerDecisionTree(byType.Expression, byType.WhenNull);
if (byType.WhenNull?.MatchIsComplete != true)
{
_loweredDecisionTree.Add(_factory.Goto(defaultLabel));
}
_loweredDecisionTree.Add(_factory.Label(notNullLabel));
}
else
{
Debug.Assert(byType.WhenNull == null);
}
foreach (var td in byType.TypeAndDecision)
{
// then test for each type, sequentially
var type = td.Key;
var decision = td.Value;
var failLabel = _factory.GenerateLabel("failedDecision");
var testAndCopy = TypeTestAndCopyToTemp(byType.Expression, decision.Expression);
_loweredDecisionTree.Add(_factory.ConditionalGoto(testAndCopy, failLabel, false));
LowerDecisionTree(decision.Expression, decision);
_loweredDecisionTree.Add(_factory.Label(failLabel));
}
// finally, the default for when no type matches
_loweredDecisionTree.Add(_factory.Label(defaultLabel));
LowerDecisionTree(byType.Expression, byType.Default);
}
}