/// <summary>
/// Performs a move out operation on the goto statement. For more information see
/// Chapter 2.2.1 "Outward-movement Transformations"
/// </summary>
/// <param name="gotoStatement"></param>
/// <param name="label"></param>
private void MoveOut(IfStatement gotoStatement, string label)
{
/// Preprocessing.
BlockStatement containingBlock = gotoStatement.Parent as BlockStatement;
BlockStatement outerBlock = GetOuterBlock(containingBlock);
VariableReferenceExpression conditionVar = new VariableReferenceExpression(GetLabelVariable(label), null);
ExtractConditionIntoVariable(conditionVar.CloneExpressionOnly() as VariableReferenceExpression, gotoStatement, containingBlock);
Statement oldEnclosingStatement = containingBlock.Parent;
if (oldEnclosingStatement is SwitchCase)
{
oldEnclosingStatement = oldEnclosingStatement.Parent;
}
if (containingBlock.Parent is SwitchCase || containingBlock.Parent is WhileStatement || containingBlock.Parent is DoWhileStatement || containingBlock.Parent is ForStatement
|| containingBlock.Parent is ForEachStatement)
{
/// Then we can exit using break.
/// Create the if - break.
BlockStatement thenBlock = new BlockStatement();
thenBlock.AddStatement(new BreakStatement(null)); //might have to keep track of brakes
IfStatement breakIf = new IfStatement(conditionVar.CloneExpressionOnly(), thenBlock, null);
/// Replace the original goto
int gotoIndex = containingBlock.Statements.IndexOf(gotoStatement);
containingBlock.Statements.Remove(gotoStatement);
containingBlock.AddStatementAt(gotoIndex, breakIf);
}
else if (containingBlock.Parent is IfStatement || containingBlock.Parent is TryStatement || containingBlock.Parent is IfElseIfStatement)
{
/// Then we can exit via introducing another condition.
int gotoIndex = containingBlock.Statements.IndexOf(gotoStatement);
int index = gotoIndex + 1;
BlockStatement thenBlock = new BlockStatement();
while (index < containingBlock.Statements.Count)
{
thenBlock.AddStatement(containingBlock.Statements[index]);
containingBlock.Statements.RemoveAt(index);
}
UnaryExpression condition = new UnaryExpression(UnaryOperator.LogicalNot, conditionVar.CloneExpressionOnly(), null);
IfStatement innerIf = new IfStatement(condition, thenBlock, null);
/// At this point the goto statement should be the last one in the block.
/// Simply replace it with the new if.
containingBlock.Statements.Remove(gotoStatement);
/// If the then block is empty, the if should not be added.
if (innerIf.Then.Statements.Count != 0)
{
containingBlock.AddStatement(innerIf);
}
}
else
{
throw new ArgumentOutOfRangeException("Goto statement can not leave this parent construct.");
}
/// Add the goto statement after the construct.
/// The goto statement shoud be detached from the AST at this point.
outerBlock.AddStatementAt(outerBlock.Statements.IndexOf(oldEnclosingStatement) + 1, gotoStatement);
}
/// <summary>
/// Performs a move-in transformation as described in Chapter 2.2.2 in <see cref="Taming Control Flow A Structured Approach to Eliminating Goto Statements.pdf"/>.
/// </summary>
/// <param name="gotoStatement">The goto statement to be moved in.</param>
/// <param name="targetStatement">The statement that the goto will move in.</param>
/// <param name="label">The target label.</param>
private void MoveIn(IfStatement gotoStatement, Statement targetStatement, string label)
{
/// Preprocessing.
BlockStatement containingBlock = gotoStatement.Parent as BlockStatement;
VariableReferenceExpression conditionVar = new VariableReferenceExpression(GetLabelVariable(label), null);
/// Create the statement conditionVariable = originalCondition;
/// Add the assigning statement before gotoStatement and replace originalCondition with conditionVariable
ExtractConditionIntoVariable(conditionVar.CloneExpressionOnly() as VariableReferenceExpression, gotoStatement, containingBlock);
/// Collect the statements between the goto jump and the target statement.
int gotoIndex = containingBlock.Statements.IndexOf(gotoStatement);
int targetIndex = containingBlock.Statements.IndexOf(targetStatement);
BlockStatement thenBlock = CollectStatements(gotoIndex + 1, targetIndex, containingBlock);
/// Create the new if.
IfStatement outerIfStatement =
new IfStatement(new UnaryExpression(UnaryOperator.LogicalNot, conditionVar.CloneExpressionOnly(), null), thenBlock, null);
/// Replace the old goto with the new if statement.
if (outerIfStatement.Then.Statements.Count > 0)
{
containingBlock.AddStatementAt(gotoIndex, outerIfStatement);
}
containingBlock.Statements.Remove(gotoStatement);
/// At this point the original goto statement is completely detached from the AST. It must be reattached as the first statement in the target.
if (targetStatement is DoWhileStatement)
{
/// Loops with more than one entry can be created only by this step, so the do-while loops is the only one
/// that must be considered.
(targetStatement as DoWhileStatement).Body.AddStatementAt(0, gotoStatement);
}
else if (targetStatement is IfStatement)
{
/// If statements with more than one entry to then/else blocks can be created only by this step, so that's why
/// the only case that must be considered is the case when the target is in the then block.
IfStatement targetIf = targetStatement as IfStatement;
targetIf.Condition = UpdateCondition(targetIf.Condition, conditionVar.CloneExpressionOnly() as VariableReferenceExpression); /// This greatly depends on the short-circut evaluation.
targetIf.Then.AddStatementAt(0, gotoStatement);
}
else if (targetStatement is SwitchCase)
{
MoveInCase(gotoStatement, targetStatement as SwitchCase, label);
}
else if (targetStatement is WhileStatement)
{
/// This case should not be reachable.
WhileStatement @while = targetStatement as WhileStatement;
@while.Body.AddStatementAt(0, gotoStatement);
@while.Condition = UpdateCondition(@while.Condition, conditionVar.CloneExpressionOnly() as VariableReferenceExpression);
}
else
{
throw new NotSupportedException("Unsupported target statement for goto jump.");
}
}
/// <summary>
/// Contains the logic for moving a goto inside the case of switch statement. For more information
/// see Chapter "2.2.2 Inward-movement Transformations : Moving a goto into a switch statement" from
/// <see cref="Taming Control Flow A Structured Approach to Eliminating Goto Statements.pdf"/>.
/// </summary>
/// <param name="gotoStatement">The goto statement to be moved in.</param>
/// <param name="switchCase">The switch case that contains the target of the goto statement.</param>
/// <param name="label">The label of the target.</param>
private void MoveInCase(IfStatement gotoStatement, SwitchCase switchCase, string label)
{
VariableReferenceExpression conditionVariable = new VariableReferenceExpression(GetLabelVariable(label), null);
BlockStatement containingBlock = GetOuterBlock(gotoStatement);
SwitchStatement switchStatement = switchCase.Parent as SwitchStatement;
int gotoIndex = containingBlock.Statements.IndexOf(gotoStatement);
int switchIndex = containingBlock.Statements.IndexOf(switchStatement);
/// Generate variable and extract the switch condition
string switchVariableName = "switch" + switchStatement.ConditionBlock.First.Offset;
TypeReference switchVariableType = GetSwitchType(switchStatement);
VariableDefinition switchVariable = new VariableDefinition(switchVariableName, switchVariableType);
switchVariables.Add(switchVariable);
VariableReferenceExpression switchVarEx = new VariableReferenceExpression(switchVariable, null);
ExtractConditionIntoVariable(switchVarEx, switchStatement, containingBlock);
BlockStatement thenBlock = CollectStatements(gotoIndex + 1, switchIndex + 1, containingBlock);
BlockStatement elseBlock = new BlockStatement();
/// Adds swCond = caseCond; in the last part of else.
BinaryExpression assignSwitchVariable = new BinaryExpression(BinaryOperator.Assign, switchVarEx.CloneExpressionOnly(), GetCaseConditionExpression(switchCase), typeSystem, null);
elseBlock.AddStatement(new ExpressionStatement(assignSwitchVariable));
IfStatement precedingIf = new IfStatement(new UnaryExpression(UnaryOperator.LogicalNot, conditionVariable, null), thenBlock, elseBlock);
/// Attach new if and move the goto conditional.
/// Attach it only if the then block is not empty.
if (precedingIf.Then.Statements.Count != 0)
{
containingBlock.AddStatementAt(gotoIndex, precedingIf);
}
containingBlock.Statements.Remove(gotoStatement);
switchCase.Body.AddStatementAt(0, gotoStatement);
}
/// <summary>
/// Extracts the condition of the condition statement into new variable. Replaces the condition of the statement with the new variable and inserts
/// the assignment statement right before the condition statement.
/// </summary>
/// <param name="conditionVar">The variable which should be assigned the condition.</param>
/// <param name="gotoStatement">The conditional goto.</param>
/// <param name="containingBlock">The block that contains the conditional goto.</param>
private void ExtractConditionIntoVariable(VariableReferenceExpression conditionVar, ConditionStatement statement, BlockStatement containingBlock)
{
/// Create the statement conditionVariable = originalCondition;
BinaryExpression conditionAssignment = new BinaryExpression(BinaryOperator.Assign, conditionVar, statement.Condition, typeSystem, null);
ExpressionStatement assignStatement = new ExpressionStatement(conditionAssignment);
/// Insert the statement before the original goto statement.
int gotoIndex = containingBlock.Statements.IndexOf(statement);
containingBlock.AddStatementAt(gotoIndex, assignStatement);
/// Update the condition of the goto statement.
statement.Condition = conditionVar.CloneExpressionOnly();
}
