/// <summary>
/// Visit a boolean condition expression, where we will be wanting AssignedWhenTrue and
/// AssignedWhenFalse.
/// </summary>
/// <param name="node"></param>
protected void VisitCondition(BoundExpression node)
{
Debug.Assert(!this.state.Assigned.IsNull);
Visit(node);
// We implement the foundational rules missing from the language specification:
// v is "definitely assigned when true" after a constant expression whose value is false.
// v is "definitely assigned when false" after a constant expression whose value is true.
// These rules are to be added to the language specification.
// It was the lack of these foundational rules that led to the invention of the concept
// of "unreachable expression" in the native compiler.
if (IsConstantTrue(node))
{
state.Merge();
this.state = new FlowAnalysisLocalState(this.state.Reachable, this.state.Assigned, BitArray.AllSet(nextVariableSlot));
}
else if (IsConstantFalse(node))
{
state.Merge();
this.state = new FlowAnalysisLocalState(this.state.Reachable, BitArray.AllSet(nextVariableSlot), this.state.Assigned);
}
else
{
state.Split();
}
}
/// <summary>
/// Create a new "unreachable" state, in which every variable slot (up to nextVariableSlot)
/// is treated as assigned.
/// </summary>
/// <param name="nextVariableSlot"></param>
/// <returns></returns>
public static FlowAnalysisLocalState UnreachableState(int nextVariableSlot)
{
FlowAnalysisLocalState result;
result.Reachable = false;
result.Assigned = BitArray.AllSet(nextVariableSlot);
result.AssignedWhenTrue = result.AssignedWhenFalse = BitArray.Null;
return(result);
}
public override object VisitForStatement(BoundForStatement node, object arg)
{
VisitStatement(node.Initializer);
LoopHead(node);
bool isTrue;
bool isFalse;
if (node.Condition != null)
{
isFalse = IsConstantFalse(node.Condition);
isTrue = IsConstantTrue(node.Condition);
VisitCondition(node.Condition);
}
else
{
isTrue = true;
isFalse = false;
this.state = new FlowAnalysisLocalState(this.state.Reachable, this.state.Assigned, BitArray.AllSet(nextVariableSlot));
}
var bodyState = new FlowAnalysisLocalState(this.state.Reachable && !isFalse, this.state.AssignedWhenTrue);
var breakState = new FlowAnalysisLocalState(this.state.Reachable && !isTrue, this.state.AssignedWhenFalse);
var oldPendingBranches = this.pendingBranches;
this.pendingBranches = ArrayBuilder <PendingBranch> .GetInstance();
this.state = bodyState;
VisitStatement(node.Body);
ResolveContinues(node.ContinueLabel);
VisitStatement(node.Increment);
LoopTail(node);
ResolveBreaks(oldPendingBranches, breakState, node.BreakLabel);
return(null);
}