internal ControlFlowGraph(ControlFlowNode[] nodes)
{
this.nodes = new ReadOnlyCollection<ControlFlowNode>(nodes);
Debug.Assert(EntryPoint.NodeType == ControlFlowNodeType.EntryPoint);
Debug.Assert(RegularExit.NodeType == ControlFlowNodeType.RegularExit);
Debug.Assert(ExceptionalExit.NodeType == ControlFlowNodeType.ExceptionalExit);
}
ControlFlowGraph BuildGraph(List<ILNode> nodes, ILLabel entryLabel)
{
int index = 0;
List<ControlFlowNode> cfNodes = new List<ControlFlowNode>();
ControlFlowNode entryPoint = new ControlFlowNode(index++, 0, ControlFlowNodeType.EntryPoint);
cfNodes.Add(entryPoint);
ControlFlowNode regularExit = new ControlFlowNode(index++, -1, ControlFlowNodeType.RegularExit);
cfNodes.Add(regularExit);
ControlFlowNode exceptionalExit = new ControlFlowNode(index++, -1, ControlFlowNodeType.ExceptionalExit);
cfNodes.Add(exceptionalExit);
// Create graph nodes
labelToCfNode = new Dictionary<ILLabel, ControlFlowNode>();
Dictionary<ILNode, ControlFlowNode> astNodeToCfNode = new Dictionary<ILNode, ControlFlowNode>();
foreach(ILBasicBlock node in nodes) {
ControlFlowNode cfNode = new ControlFlowNode(index++, -1, ControlFlowNodeType.Normal);
cfNodes.Add(cfNode);
astNodeToCfNode[node] = cfNode;
cfNode.UserData = node;
// Find all contained labels
foreach (ILLabel label in node.EnumerateSelfAndChildrenRecursive().OfType<ILLabel>())
{
labelToCfNode[label] = cfNode;
}
}
// Entry endge
ControlFlowNode entryNode = labelToCfNode[entryLabel];
ControlFlowEdge entryEdge = new ControlFlowEdge(entryPoint, entryNode, JumpType.Normal);
entryPoint.Outgoing.Add(entryEdge);
entryNode.Incoming.Add(entryEdge);
// Create edges
foreach(ILBasicBlock node in nodes) {
ControlFlowNode source = astNodeToCfNode[node];
var allBranchTargets =
from e in node.EnumerateSelfAndChildrenRecursive().OfType<ILExpression>()
where e.IsBranch()
from t in e.GetBranchTargets()
select t;
// Find all branches
foreach(ILLabel target in allBranchTargets) {
ControlFlowNode destination;
// Labels which are out of out scope will not be int the collection
// Insert self edge only if we are sure we are a loop
if (labelToCfNode.TryGetValue(target, out destination) && (destination != source || target == node.Body.FirstOrDefault())) {
ControlFlowEdge edge = new ControlFlowEdge(source, destination, JumpType.Normal);
source.Outgoing.Add(edge);
destination.Incoming.Add(edge);
}
}
}
return new ControlFlowGraph(cfNodes.ToArray());
}
public ControlFlowEdge(ControlFlowNode source, ControlFlowNode target, JumpType type)
{
this.Source = source;
this.Target = target;
this.Type = type;
}
public ControlFlowEdge(ControlFlowNode source, ControlFlowNode target, JumpType type)
{
this.Source = source;
this.Target = target;
this.Type = type;
}
static HashSet<ControlFlowNode> FindLoopContent(HashSet<ControlFlowNode> scope, ControlFlowNode head)
{
var viaBackEdges = head.Predecessors.Where(p => head.Dominates(p));
HashSet<ControlFlowNode> agenda = new HashSet<ControlFlowNode>(viaBackEdges);
HashSet<ControlFlowNode> result = new HashSet<ControlFlowNode>();
while(agenda.Count > 0) {
ControlFlowNode addNode = agenda.First();
agenda.Remove(addNode);
if (scope.Contains(addNode) && head.Dominates(addNode) && result.Add(addNode)) {
foreach (var predecessor in addNode.Predecessors) {
agenda.Add(predecessor);
}
}
}
if (scope.Contains(head))
result.Add(head);
return result;
}
static HashSet<ControlFlowNode> FindDominatedNodes(HashSet<ControlFlowNode> scope, ControlFlowNode head)
{
HashSet<ControlFlowNode> agenda = new HashSet<ControlFlowNode>();
HashSet<ControlFlowNode> result = new HashSet<ControlFlowNode>();
agenda.Add(head);
while(agenda.Count > 0) {
ControlFlowNode addNode = agenda.First();
agenda.Remove(addNode);
if (scope.Contains(addNode) && head.Dominates(addNode) && result.Add(addNode)) {
foreach (var successor in addNode.Successors) {
agenda.Add(successor);
}
}
}
return result;
}
List<ILNode> FindConditions(HashSet<ControlFlowNode> scope, ControlFlowNode entryNode)
{
List<ILNode> result = new List<ILNode>();
// Do not modify entry data
scope = new HashSet<ControlFlowNode>(scope);
HashSet<ControlFlowNode> agenda = new HashSet<ControlFlowNode>();
agenda.Add(entryNode);
while(agenda.Any()) {
ControlFlowNode node = agenda.First();
// Attempt for a good order
while(agenda.Contains(node.ImmediateDominator)) {
node = node.ImmediateDominator;
}
agenda.Remove(node);
// 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
HashSet<ControlFlowNode> frontiers = new HashSet<ControlFlowNode>();
if (trueTarget != null)
frontiers.UnionWith(trueTarget.DominanceFrontier.Except(new [] { trueTarget }));
if (falseTarget != null)
frontiers.UnionWith(falseTarget.DominanceFrontier.Except(new [] { falseTarget }));
if (trueTarget != null && !frontiers.Contains(trueTarget)) {
HashSet<ControlFlowNode> content = FindDominatedNodes(scope, trueTarget);
scope.ExceptWith(content);
ilCond.TrueBlock.Body.AddRange(FindConditions(content, trueTarget));
}
if (falseTarget != null && !frontiers.Contains(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);
}
}
// Using the dominator tree should ensure we find the the widest loop first
foreach(var child in node.DominatorTreeChildren) {
agenda.Add(child);
}
}
// Add whatever is left
foreach(var node in scope) {
result.Add((ILNode)node.UserData);
}
return result;
}
List<ILNode> FindLoops(HashSet<ControlFlowNode> scope, ControlFlowNode entryPoint, bool excludeEntryPoint)
{
List<ILNode> result = new List<ILNode>();
// Do not modify entry data
scope = new HashSet<ControlFlowNode>(scope);
Queue<ControlFlowNode> agenda = new Queue<ControlFlowNode>();
agenda.Enqueue(entryPoint);
while(agenda.Count > 0) {
ControlFlowNode node = agenda.Dequeue();
// If the node is a loop header
if (scope.Contains(node)
&& node.DominanceFrontier.Contains(node)
&& (node != entryPoint || !excludeEntryPoint))
{
HashSet<ControlFlowNode> loopContents = FindLoopContent(scope, node);
// If the first expression is a loop condition
ILBasicBlock basicBlock = (ILBasicBlock)node.UserData;
ILExpression condExpr;
ILLabel trueLabel;
ILLabel falseLabel;
// It has to be just brtrue - any preceding code would introduce goto
if(basicBlock.MatchSingleAndBr(ILCode.Brtrue, out trueLabel, out condExpr, out falseLabel))
{
ControlFlowNode trueTarget;
labelToCfNode.TryGetValue(trueLabel, out trueTarget);
ControlFlowNode falseTarget;
labelToCfNode.TryGetValue(falseLabel, out falseTarget);
// If one point inside the loop and the other outside
if ((!loopContents.Contains(trueTarget) && loopContents.Contains(falseTarget)) ||
(loopContents.Contains(trueTarget) && !loopContents.Contains(falseTarget)) )
{
loopContents.RemoveOrThrow(node);
scope.RemoveOrThrow(node);
// If false means enter the loop
if (loopContents.Contains(falseTarget) || falseTarget == node)
{
// Negate the condition
condExpr = new ILExpression(ILCode.LogicNot, null, condExpr);
ILLabel tmp = trueLabel;
trueLabel = falseLabel;
falseLabel = tmp;
}
ControlFlowNode postLoopTarget;
labelToCfNode.TryGetValue(falseLabel, out postLoopTarget);
if (postLoopTarget != null) {
// Pull more nodes into the loop
HashSet<ControlFlowNode> postLoopContents = FindDominatedNodes(scope, postLoopTarget);
var pullIn = scope.Except(postLoopContents).Where(n => node.Dominates(n));
loopContents.UnionWith(pullIn);
}
// Use loop to implement the brtrue
basicBlock.Body.RemoveTail(ILCode.Brtrue, ILCode.Br);
basicBlock.Body.Add(new ILWhileLoop() {
Condition = condExpr,
BodyBlock = new ILBlock() {
EntryGoto = new ILExpression(ILCode.Br, trueLabel),
Body = FindLoops(loopContents, node, false)
}
});
basicBlock.Body.Add(new ILExpression(ILCode.Br, falseLabel));
result.Add(basicBlock);
scope.ExceptWith(loopContents);
}
}
// Fallback method: while(true)
if (scope.Contains(node)) {
result.Add(new ILBasicBlock() {
Body = new List<ILNode>() {
new ILLabel() { Name = "Loop_" + (nextLabelIndex++) },
new ILWhileLoop() {
BodyBlock = new ILBlock() {
EntryGoto = new ILExpression(ILCode.Br, (ILLabel)basicBlock.Body.First()),
Body = FindLoops(loopContents, node, true)
}
},
},
});
scope.ExceptWith(loopContents);
}
}
// Using the dominator tree should ensure we find the the widest loop first
foreach(var child in node.DominatorTreeChildren) {
agenda.Enqueue(child);
}
}
// Add whatever is left
foreach(var node in scope) {
result.Add((ILNode)node.UserData);
}
scope.Clear();
return result;
}
/// <summary>
/// Gets whether <c>this</c> dominates <paramref name="node"/>.
/// </summary>
public bool Dominates(ControlFlowNode node)
{
// TODO: this can be made O(1) by numbering the dominator tree
ControlFlowNode tmp = node;
while (tmp != null) {
if (tmp == this)
return true;
tmp = tmp.ImmediateDominator;
}
return false;
}
internal ControlFlowNode(int blockIndex, ExceptionHandler exceptionHandler, ControlFlowNode endFinallyOrFaultNode)
{
this.BlockIndex = blockIndex;
this.NodeType = endFinallyOrFaultNode != null ? ControlFlowNodeType.FinallyOrFaultHandler : ControlFlowNodeType.CatchHandler;
this.ExceptionHandler = exceptionHandler;
this.EndFinallyOrFaultNode = endFinallyOrFaultNode;
Debug.Assert((exceptionHandler.HandlerType == ExceptionHandlerType.Finally || exceptionHandler.HandlerType == ExceptionHandlerType.Fault) == (endFinallyOrFaultNode != null));
this.Offset = exceptionHandler.HandlerStart.Offset;
}
static ControlFlowNode FindCommonDominator(ControlFlowNode b1, ControlFlowNode b2)
{
// Here we could use the postorder numbers to get rid of the hashset, see "A Simple, Fast Dominance Algorithm"
HashSet<ControlFlowNode> path1 = new HashSet<ControlFlowNode>();
while (b1 != null && path1.Add(b1))
b1 = b1.ImmediateDominator;
while (b2 != null) {
if (path1.Contains(b2))
return b2;
else
b2 = b2.ImmediateDominator;
}
throw new Exception("No common dominator found!");
}