/// <summary>
/// Responsible for detecting switch cases with values that are actually also the default case
/// </summary>
static void AnointDefaultSwitchCases(ILSwitch swtch)
{
var defaultCase = swtch.CaseBlocks.FirstOrDefault((cse) => cse.IsDefault);
if (defaultCase == null)
{
return;
}
var lastBlock = defaultCase.Body.LastOrDefault() as ILBasicBlock;
if (
(lastBlock != null) &&
(lastBlock.Body.Count == 2) &&
(lastBlock.Body[0] is ILLabel) &&
(lastBlock.Body[1] is ILExpression) &&
(((ILExpression)lastBlock.Body[1]).Code == ILCode.LoopOrSwitchBreak)
)
{
// This is a delegating default case. Ensure the target is another case in this switch block.
var targetCase = swtch.CaseBlocks.FirstOrDefault(
(cse) => (
(cse.EntryGoto.Operand == defaultCase.EntryGoto.Operand) &&
(cse != defaultCase)
)
);
if (targetCase != null)
{
// The target is another case in this switch block, so fold the current case into that one.
swtch.CaseBlocks.Remove(defaultCase);
targetCase.IsDefault = true;
}
}
}
/// <summary>
/// Get the first expression to be excecuted if the instruction pointer is at the start of the given node.
/// Try blocks may not be entered in any way. If possible, the try block is returned as the node to be executed.
/// </summary>
ILNode Enter(ILNode node, HashSet <ILNode> visitedNodes)
{
if (node == null)
{
throw new ArgumentNullException();
}
if (!visitedNodes.Add(node))
{
return(null); // Infinite loop
}
ILLabel label = node as ILLabel;
if (label != null)
{
return(Exit(label, visitedNodes));
}
ILExpression expr = node as ILExpression;
if (expr != null)
{
if (expr.Code == ILCode.Br || expr.Code == ILCode.Leave)
{
ILLabel target = (ILLabel)expr.Operand;
// Early exit - same try-block
if (GetParents(expr).OfType <ILTryCatchBlock>().FirstOrDefault() == GetParents(target).OfType <ILTryCatchBlock>().FirstOrDefault())
{
return(Enter(target, visitedNodes));
}
// Make sure we are not entering any try-block
var srcTryBlocks = GetParents(expr).OfType <ILTryCatchBlock>().Reverse().ToList();
var dstTryBlocks = GetParents(target).OfType <ILTryCatchBlock>().Reverse().ToList();
// Skip blocks that we are already in
int i = 0;
while (i < srcTryBlocks.Count && i < dstTryBlocks.Count && srcTryBlocks[i] == dstTryBlocks[i])
{
i++;
}
if (i == dstTryBlocks.Count)
{
return(Enter(target, visitedNodes));
}
else
{
ILTryCatchBlock dstTryBlock = dstTryBlocks[i];
// Check that the goto points to the start
ILTryCatchBlock current = dstTryBlock;
while (current != null)
{
foreach (ILNode n in current.TryBlock.Body)
{
if (n is ILLabel)
{
if (n == target)
{
return(dstTryBlock);
}
}
else if (!n.Match(ILCode.Nop))
{
current = n as ILTryCatchBlock;
break;
}
}
}
return(null);
}
}
else if (expr.Code == ILCode.Nop)
{
return(Exit(expr, visitedNodes));
}
else if (expr.Code == ILCode.LoopOrSwitchBreak)
{
ILNode breakBlock = GetParents(expr).First(n => n is ILWhileLoop || n is ILSwitch);
return(Exit(breakBlock, new HashSet <ILNode>()
{
expr
}));
}
else if (expr.Code == ILCode.LoopContinue)
{
ILNode continueBlock = GetParents(expr).First(n => n is ILWhileLoop);
return(Enter(continueBlock, new HashSet <ILNode>()
{
expr
}));
}
else
{
return(expr);
}
}
ILBlock block = node as ILBlock;
if (block != null)
{
if (block.EntryGoto != null)
{
return(Enter(block.EntryGoto, visitedNodes));
}
else if (block.Body.Count > 0)
{
return(Enter(block.Body[0], visitedNodes));
}
else
{
return(Exit(block, visitedNodes));
}
}
ILCondition cond = node as ILCondition;
if (cond != null)
{
return(cond.Condition);
}
ILWhileLoop loop = node as ILWhileLoop;
if (loop != null)
{
if (loop.Condition != null)
{
return(loop.Condition);
}
else
{
return(Enter(loop.BodyBlock, visitedNodes));
}
}
ILTryCatchBlock tryCatch = node as ILTryCatchBlock;
if (tryCatch != null)
{
return(tryCatch);
}
ILSwitch ilSwitch = node as ILSwitch;
if (ilSwitch != null)
{
return(ilSwitch.Condition);
}
throw new NotSupportedException(node.GetType().ToString());
}
List <ILNode> FindConditions(HashSet <ControlFlowNode> scope, ControlFlowNode entryNode)
{
List <ILNode> result = new List <ILNode>();
// Do not modify entry data
scope = new HashSet <ControlFlowNode>(scope);
Stack <ControlFlowNode> agenda = new Stack <ControlFlowNode>();
agenda.Push(entryNode);
while (agenda.Count > 0)
{
ControlFlowNode node = agenda.Pop();
// Find a block that represents a simple condition
if (scope.Contains(node))
{
ILBasicBlock block = (ILBasicBlock)node.UserData;
{
// Switch
ILLabel[] caseLabels;
ILExpression switchArg;
ILLabel fallLabel;
if (block.MatchLastAndBr(ILCode.Switch, out caseLabels, out switchArg, out fallLabel))
{
// Replace the switch code with ILSwitch
ILSwitch ilSwitch = new ILSwitch()
{
Condition = switchArg
};
block.Body.RemoveTail(ILCode.Switch, ILCode.Br);
block.Body.Add(ilSwitch);
block.Body.Add(new ILExpression(ILCode.Br, fallLabel));
result.Add(block);
// Remove the item so that it is not picked up as content
scope.RemoveOrThrow(node);
// Find the switch offset
int addValue = 0;
List <ILExpression> subArgs;
if (ilSwitch.Condition.Match(ILCode.Sub, out subArgs) && subArgs[1].Match(ILCode.Ldc_I4, out addValue))
{
ilSwitch.Condition = subArgs[0];
}
// Pull in code of cases
ControlFlowNode fallTarget = null;
labelToCfNode.TryGetValue(fallLabel, out fallTarget);
HashSet <ControlFlowNode> frontiers = new HashSet <ControlFlowNode>();
if (fallTarget != null)
{
frontiers.UnionWith(fallTarget.DominanceFrontier.Except(new [] { fallTarget }));
}
foreach (ILLabel condLabel in caseLabels)
{
ControlFlowNode condTarget = null;
labelToCfNode.TryGetValue(condLabel, out condTarget);
if (condTarget != null)
{
frontiers.UnionWith(condTarget.DominanceFrontier.Except(new [] { condTarget }));
}
}
for (int i = 0; i < caseLabels.Length; i++)
{
ILLabel condLabel = caseLabels[i];
// Find or create new case block
ILSwitch.CaseBlock caseBlock = ilSwitch.CaseBlocks.FirstOrDefault(b => b.EntryGoto.Operand == condLabel);
if (caseBlock == null)
{
caseBlock = new ILSwitch.CaseBlock()
{
Values = new List <int>(),
EntryGoto = new ILExpression(ILCode.Br, condLabel)
};
ilSwitch.CaseBlocks.Add(caseBlock);
ControlFlowNode condTarget = null;
labelToCfNode.TryGetValue(condLabel, out condTarget);
if (condTarget != null && !frontiers.Contains(condTarget))
{
HashSet <ControlFlowNode> content = FindDominatedNodes(scope, condTarget);
scope.ExceptWith(content);
caseBlock.Body.AddRange(FindConditions(content, condTarget));
// Add explicit break which should not be used by default, but the goto removal might decide to use it
caseBlock.Body.Add(new ILBasicBlock()
{
Body =
{
new ILLabel()
{
Name = "SwitchBreak_" + (nextLabelIndex++)
},
new ILExpression(ILCode.LoopOrSwitchBreak, null)
}
});
}
}
caseBlock.Values.Add(i + addValue);
}
// Heuristis to determine if we want to use fallthough as default case
if (fallTarget != null && !frontiers.Contains(fallTarget))
{
HashSet <ControlFlowNode> content = FindDominatedNodes(scope, fallTarget);
if (content.Any())
{
var caseBlock = new ILSwitch.CaseBlock()
{
EntryGoto = new ILExpression(ILCode.Br, fallLabel)
};
ilSwitch.CaseBlocks.Add(caseBlock);
block.Body.RemoveTail(ILCode.Br);
scope.ExceptWith(content);
caseBlock.Body.AddRange(FindConditions(content, fallTarget));
// Add explicit break which should not be used by default, but the goto removal might decide to use it
caseBlock.Body.Add(new ILBasicBlock()
{
Body =
{
new ILLabel()
{
Name = "SwitchBreak_" + (nextLabelIndex++)
},
new ILExpression(ILCode.LoopOrSwitchBreak, null)
}
});
}
}
}
// Two-way branch
ILExpression condExpr;
ILLabel trueLabel;
ILLabel falseLabel;
if (block.MatchLastAndBr(ILCode.Brtrue, out trueLabel, out condExpr, out falseLabel))
{
// Swap bodies since that seems to be the usual C# order
ILLabel temp = trueLabel;
trueLabel = falseLabel;
falseLabel = temp;
condExpr = new ILExpression(ILCode.LogicNot, null, condExpr);
// Convert the brtrue to ILCondition
ILCondition ilCond = new ILCondition()
{
Condition = condExpr,
TrueBlock = new ILBlock()
{
EntryGoto = new ILExpression(ILCode.Br, trueLabel)
},
FalseBlock = new ILBlock()
{
EntryGoto = new ILExpression(ILCode.Br, falseLabel)
}
};
block.Body.RemoveTail(ILCode.Brtrue, ILCode.Br);
block.Body.Add(ilCond);
result.Add(block);
// Remove the item immediately so that it is not picked up as content
scope.RemoveOrThrow(node);
ControlFlowNode trueTarget = null;
labelToCfNode.TryGetValue(trueLabel, out trueTarget);
ControlFlowNode falseTarget = null;
labelToCfNode.TryGetValue(falseLabel, out falseTarget);
// Pull in the conditional code
if (trueTarget != null && HasSingleEdgeEnteringBlock(trueTarget))
{
HashSet <ControlFlowNode> content = FindDominatedNodes(scope, trueTarget);
scope.ExceptWith(content);
ilCond.TrueBlock.Body.AddRange(FindConditions(content, trueTarget));
}
if (falseTarget != null && HasSingleEdgeEnteringBlock(falseTarget))
{
HashSet <ControlFlowNode> content = FindDominatedNodes(scope, falseTarget);
scope.ExceptWith(content);
ilCond.FalseBlock.Body.AddRange(FindConditions(content, falseTarget));
}
}
}
// Add the node now so that we have good ordering
if (scope.Contains(node))
{
result.Add((ILNode)node.UserData);
scope.Remove(node);
}
}
// depth-first traversal of dominator tree
for (int i = node.DominatorTreeChildren.Count - 1; i >= 0; i--)
{
agenda.Push(node.DominatorTreeChildren[i]);
}
}
// Add whatever is left
foreach (var node in scope)
{
result.Add((ILNode)node.UserData);
}
return(result);
}
