private BoundExpression VisitConditionalOperator(BoundConditionalOperator node)
{
var condition = Visit(node.Condition);
var consequence = VisitExactType(node.Consequence);
var alternative = VisitExactType(node.Alternative);
return(ExprFactory("Condition", condition, consequence, alternative));
}
public override BoundNode VisitConditionalOperator(BoundConditionalOperator node)
{
BoundSpillSequenceBuilder conditionBuilder = null;
var condition = VisitExpression(ref conditionBuilder, node.Condition);
BoundSpillSequenceBuilder consequenceBuilder = null;
var consequence = VisitExpression(ref consequenceBuilder, node.Consequence);
BoundSpillSequenceBuilder alternativeBuilder = null;
var alternative = VisitExpression(ref alternativeBuilder, node.Alternative);
if (consequenceBuilder == null && alternativeBuilder == null)
{
return(UpdateExpression(conditionBuilder, node.Update(node.IsRef, condition, consequence, alternative, node.ConstantValueOpt, node.Type)));
}
if (conditionBuilder == null)
{
conditionBuilder = new BoundSpillSequenceBuilder();
}
if (consequenceBuilder == null)
{
consequenceBuilder = new BoundSpillSequenceBuilder();
}
if (alternativeBuilder == null)
{
alternativeBuilder = new BoundSpillSequenceBuilder();
}
if (node.Type.SpecialType == SpecialType.System_Void)
{
conditionBuilder.AddStatement(
_F.If(condition,
UpdateStatement(consequenceBuilder, _F.ExpressionStatement(consequence)),
UpdateStatement(alternativeBuilder, _F.ExpressionStatement(alternative))));
return(conditionBuilder.Update(_F.Default(node.Type)));
}
else
{
var tmp = _F.SynthesizedLocal(node.Type, kind: SynthesizedLocalKind.Spill, syntax: _F.Syntax);
conditionBuilder.AddLocal(tmp);
conditionBuilder.AddStatement(
_F.If(condition,
UpdateStatement(consequenceBuilder, _F.Assignment(_F.Local(tmp), consequence)),
UpdateStatement(alternativeBuilder, _F.Assignment(_F.Local(tmp), alternative))));
return(conditionBuilder.Update(_F.Local(tmp)));
}
}
/// <summary>
/// If the condition has a constant value, then just use the selected branch.
/// e.g. "true ? x : y" becomes "x".
/// </summary>
public override BoundNode VisitConditionalOperator(BoundConditionalOperator node)
{
// just a fact, not a requirement (VisitExpression would have rewritten otherwise)
Debug.Assert(node.ConstantValue == null);
var rewrittenCondition = VisitExpression(node.Condition);
var rewrittenConsequence = VisitExpression(node.Consequence);
var rewrittenAlternative = VisitExpression(node.Alternative);
if (rewrittenCondition.ConstantValue == null)
{
return(node.Update(node.IsRef, rewrittenCondition, rewrittenConsequence, rewrittenAlternative, node.ConstantValueOpt, node.Type));
}
return(RewriteConditionalOperator(
node.Syntax,
rewrittenCondition,
rewrittenConsequence,
rewrittenAlternative,
node.ConstantValueOpt,
node.Type,
node.IsRef));
}
private BoundExpression OptimizeLiftedUnaryOperator(
UnaryOperatorKind operatorKind,
SyntaxNode syntax,
MethodSymbol method,
BoundExpression loweredOperand,
TypeSymbol type)
{
if (NullableNeverHasValue(loweredOperand))
{
return(new BoundDefaultExpression(syntax, null, type));
}
// Second, another simple optimization. If we know that the operand is never null
// then we can obtain the non-null value and skip generating the temporary. That is,
// "~(new int?(M()))" is the same as "new int?(~M())".
BoundExpression neverNull = NullableAlwaysHasValue(loweredOperand);
if (neverNull != null)
{
return(GetLiftedUnaryOperatorConsequence(operatorKind, syntax, method, type, neverNull));
}
var conditionalLeft = loweredOperand as BoundLoweredConditionalAccess;
// NOTE: we could in theory handle side-effecting loweredRight here too
// by including it as a part of whenNull, but there is a concern
// that it can lead to code duplication
var optimize = conditionalLeft != null &&
(conditionalLeft.WhenNullOpt == null || conditionalLeft.WhenNullOpt.IsDefaultValue());
if (optimize)
{
var result = LowerLiftedUnaryOperator(operatorKind, syntax, method, conditionalLeft.WhenNotNull, type);
return(conditionalLeft.Update(
conditionalLeft.Receiver,
conditionalLeft.HasValueMethodOpt,
whenNotNull: result,
whenNullOpt: null,
id: conditionalLeft.Id,
type: result.Type
));
}
// This optimization is analogous to DistributeLiftedConversionIntoLiftedOperand.
// Suppose we have a lifted unary conversion whose operand is itself a lifted operation.
// That is, we have something like:
//
// int? r = - (M() + N());
//
// where M() and N() return nullable ints. We would simply codegen this as first
// creating the nullable int result of M() + N(), then checking it for nullity,
// and then doing the unary minus. That is:
//
// int? m = M();
// int? n = N();
// int? t = m.HasValue && n.HasValue ? new int?(m.Value + n.Value) : new int?();
// int? r = t.HasValue ? new int?(-t.Value) : new int?();
//
// However, we also observe that we can distribute the unary minus into both branches of
// the conditional:
//
// int? m = M();
// int? n = N();
// int? r = m.HasValue && n.HasValue ? - (new int?(m.Value + n.Value))) : - new int?();
//
// And we already optimize those! So we could reduce this to:
//
// int? m = M();
// int? n = N();
// int? r = m.HasValue && n.HasValue ? new int?(- (m.Value + n.Value)) : new int?());
//
// which avoids entirely the creation of the unnecessary nullable int and the unnecessary
// extra null check.
if (loweredOperand.Kind == BoundKind.Sequence)
{
BoundSequence seq = (BoundSequence)loweredOperand;
if (seq.Value.Kind == BoundKind.ConditionalOperator)
{
BoundConditionalOperator conditional = (BoundConditionalOperator)seq.Value;
Debug.Assert(TypeSymbol.Equals(seq.Type, conditional.Type, TypeCompareKind.ConsiderEverything2));
Debug.Assert(TypeSymbol.Equals(conditional.Type, conditional.Consequence.Type, TypeCompareKind.ConsiderEverything2));
Debug.Assert(TypeSymbol.Equals(conditional.Type, conditional.Alternative.Type, TypeCompareKind.ConsiderEverything2));
if (NullableAlwaysHasValue(conditional.Consequence) != null && NullableNeverHasValue(conditional.Alternative))
{
return(new BoundSequence(
syntax,
seq.Locals,
seq.SideEffects,
RewriteConditionalOperator(
syntax,
conditional.Condition,
MakeUnaryOperator(operatorKind, syntax, method, conditional.Consequence, type),
MakeUnaryOperator(operatorKind, syntax, method, conditional.Alternative, type),
ConstantValue.NotAvailable,
type,
isRef: false),
type));
}
}
}
return(null);
}
