//-----------------------------------------------
// If-then-else branching
//-----------------------------------------------
/// <summary>
/// Setup a branching context. All nested iterators compiled in this context must evaluate
/// to a single boolean value. However, these expressions must not push the result as a boolean
/// onto the stack. Instead, if brctxt is BranchType.True, then the expression should
/// jump to lblBranch if it evaluates to true. If brctxt is BranchType.False, then the
/// branch should happen if the evaluation result is false.
/// </summary>
public void SetBranching(BranchingContext brctxt, Label lblBranch) {
Debug.Assert(brctxt != BranchingContext.None);
this.brctxt = brctxt;
this.lblBranch = lblBranch;
}
//-----------------------------------------------
// If-then-else branching
//-----------------------------------------------
/// <summary>
/// Setup a branching context. All nested iterators compiled in this context must evaluate
/// to a single boolean value. However, these expressions must not push the result as a boolean
/// onto the stack. Instead, if brctxt is BranchType.True, then the expression should
/// jump to lblBranch if it evaluates to true. If brctxt is BranchType.False, then the
/// branch should happen if the evaluation result is false.
/// </summary>
public void SetBranching(BranchingContext brctxt, Label lblBranch)
{
Debug.Assert(brctxt != BranchingContext.None);
_brctxt = brctxt;
_lblBranch = lblBranch;
}
/// <summary>
/// Anchor any remaining labels.
/// </summary>
private void EndConjunctiveTests(BranchingContext brctxt, Label lblBranch, Label lblOnFalse)
{
switch (brctxt)
{
case BranchingContext.OnTrue:
// Anchor false label
_helper.MarkLabel(lblOnFalse);
goto case BranchingContext.OnFalse;
case BranchingContext.OnFalse:
_iterCurr.Storage = StorageDescriptor.None();
break;
case BranchingContext.None:
// Convert branch targets into push of true/false
_helper.ConvBranchToBool(lblOnFalse, false);
_iterCurr.Storage = StorageDescriptor.Stack(typeof(bool), false);
break;
}
}
/// <summary>
/// Fixup branching context for the last test in a conjunctive (Logical And) expression.
/// </summary>
private void StartLastConjunctiveTest(BranchingContext brctxt, Label lblBranch, Label lblOnFalse)
{
switch (brctxt)
{
case BranchingContext.OnTrue:
// If last condition evaluates to true, branch to true label
_iterCurr.SetBranching(BranchingContext.OnTrue, lblBranch);
break;
default:
// If last condition evalutes to false, branch to false label
// Else fall through to true code path
_iterCurr.SetBranching(BranchingContext.OnFalse, lblOnFalse);
break;
}
}
/// <summary>
/// Fixup branching context for all but the last test in a conjunctive (Logical And) expression.
/// Return a temporary label which will be passed to StartLastAndBranch() and EndAndBranch().
/// </summary>
private Label StartConjunctiveTests(BranchingContext brctxt, Label lblBranch)
{
Label lblOnFalse;
switch (brctxt)
{
case BranchingContext.OnFalse:
// If condition evaluates to false, branch to false label
_iterCurr.SetBranching(BranchingContext.OnFalse, lblBranch);
return lblBranch;
default:
// If condition evaluates to false:
// 1. Jump to new false label that will be fixed just beyond the second condition
// 2. Or, jump to code that pushes "false"
lblOnFalse = _helper.DefineLabel();
_iterCurr.SetBranching(BranchingContext.OnFalse, lblOnFalse);
return lblOnFalse;
}
}
/// <summary>
/// Start a nested iterator in a branching context and recursively generate code for the specified QilExpression node.
/// </summary>
private void NestedVisitWithBranch(QilNode nd, BranchingContext brctxt, Label lblBranch)
{
Debug.Assert(nd.XmlType.IsSingleton && !XmlILConstructInfo.Read(nd).PushToWriterLast);
StartNestedIterator(nd);
_iterCurr.SetBranching(brctxt, lblBranch);
Visit(nd);
EndNestedIterator(nd);
_iterCurr.Storage = StorageDescriptor.None();
}