void MarkReachable(ControlFlowNode node)
{
if (node.PreviousStatement != null)
reachableEndPoints.Add(node.PreviousStatement);
if (node.NextStatement != null)
reachableStatements.Add(node.NextStatement);
foreach (var edge in node.Outgoing) {
if (visitedNodes.Add(edge.To))
stack.Push(edge.To);
}
}
protected override bool CanReachModification(ControlFlowNode node, Statement start,
IDictionary<Statement, IList<Node>> modifications)
{
if (base.CanReachModification (node, start, modifications))
return true;
if (node.NextStatement != start) {
var usingStatement = node.PreviousStatement as UsingStatement;
if (usingStatement != null) {
if (modifications.ContainsKey(usingStatement))
return true;
if (usingStatement.ResourceAcquisition is Statement &&
modifications.ContainsKey ((Statement)usingStatement.ResourceAcquisition))
return true;
}
}
return false;
}
public ControlFlowEdge(ControlFlowNode source, ControlFlowNode target, JumpType type)
{
this.Source = source;
this.Target = target;
this.Type = type;
}
private void DetectSwitchBody(Block block, SwitchInstruction switchInst)
{
Debug.Assert(block.Instructions.Last() == switchInst);
ControlFlowNode h = context.ControlFlowNode; // CFG node for our switch head
Debug.Assert(h.UserData == block);
Debug.Assert(!TreeTraversal.PreOrder(h, n => n.DominatorTreeChildren).Any(n => n.Visited));
var nodesInSwitch = new List <ControlFlowNode>();
nodesInSwitch.Add(h);
h.Visited = true;
ExtendLoop(h, nodesInSwitch, out var exitPoint, isSwitch: true);
if (exitPoint != null && exitPoint.Predecessors.Count == 1 && !context.ControlFlowGraph.HasReachableExit(exitPoint))
{
// If the exit point is reachable from just one single "break;",
// it's better to move the code into the switch.
// (unlike loops which should not be nested unless necessary,
// nesting switches makes it clearer in which cases a piece of code is reachable)
nodesInSwitch.AddRange(TreeTraversal.PreOrder(exitPoint, p => p.DominatorTreeChildren));
exitPoint = null;
}
context.Step("Create BlockContainer for switch", switchInst);
// Sort blocks in the loop in reverse post-order to make the output look a bit nicer.
// (if the loop doesn't contain nested loops, this is a topological sort)
nodesInSwitch.Sort((a, b) => b.PostOrderNumber.CompareTo(a.PostOrderNumber));
Debug.Assert(nodesInSwitch[0] == h);
foreach (var node in nodesInSwitch)
{
node.Visited = false; // reset visited flag so that we can find outer loops
Debug.Assert(h.Dominates(node) || !node.IsReachable, "The switch body must be dominated by the switch head");
}
BlockContainer switchContainer = new BlockContainer();
Block newEntryPoint = new Block();
newEntryPoint.ILRange = switchInst.ILRange;
switchContainer.Blocks.Add(newEntryPoint);
newEntryPoint.Instructions.Add(switchInst);
block.Instructions[block.Instructions.Count - 1] = switchContainer;
Block exitTargetBlock = (Block)exitPoint?.UserData;
if (exitTargetBlock != null)
{
block.Instructions.Add(new Branch(exitTargetBlock));
}
MoveBlocksIntoContainer(nodesInSwitch, switchContainer);
// Rewrite branches within the loop from oldEntryPoint to newEntryPoint:
foreach (var branch in switchContainer.Descendants.OfType <Branch>())
{
if (branch.TargetBlock == exitTargetBlock)
{
branch.ReplaceWith(new Leave(switchContainer)
{
ILRange = branch.ILRange
});
}
}
}
/// <summary>
/// Check whether 'block' is a loop head; and construct a loop instruction
/// (nested BlockContainer) if it is.
/// </summary>
public void Run(Block block, BlockTransformContext context)
{
this.context = context;
// LoopDetection runs early enough so that block should still
// be in the original container at this point.
Debug.Assert(block.Parent == context.ControlFlowGraph.Container);
this.currentBlockContainer = context.ControlFlowGraph.Container;
// Because this is a post-order block transform, we can assume that
// any nested loops within this loop have already been constructed.
if (block.Instructions.Last() is SwitchInstruction switchInst)
{
// Switch instructions support "break;" just like loops
DetectSwitchBody(block, switchInst);
}
ControlFlowNode h = context.ControlFlowNode; // CFG node for our potential loop head
Debug.Assert(h.UserData == block);
Debug.Assert(!TreeTraversal.PreOrder(h, n => n.DominatorTreeChildren).Any(n => n.Visited));
List <ControlFlowNode> loop = null;
foreach (var t in h.Predecessors)
{
if (h.Dominates(t))
{
// h->t is a back edge, and h is a loop header
// Add the natural loop of t->h to the loop.
// Definitions:
// * A back edge is an edge t->h so that h dominates t.
// * The natural loop of the back edge is the smallest set of nodes
// that includes the back edge and has no predecessors outside the set
// except for the predecessor of the header.
if (loop == null)
{
loop = new List <ControlFlowNode>();
loop.Add(h);
// Mark loop header as visited so that the pre-order traversal
// stops at the loop header.
h.Visited = true;
}
t.TraversePreOrder(n => n.Predecessors, loop.Add);
}
}
if (loop != null)
{
var headBlock = (Block)h.UserData;
context.Step($"Construct loop with head {headBlock.Label}", headBlock);
// loop now is the union of all natural loops with loop head h.
// Try to extend the loop to reduce the number of exit points:
ExtendLoop(h, loop, out var exitPoint);
// Sort blocks in the loop in reverse post-order to make the output look a bit nicer.
// (if the loop doesn't contain nested loops, this is a topological sort)
loop.Sort((a, b) => b.PostOrderNumber.CompareTo(a.PostOrderNumber));
Debug.Assert(loop[0] == h);
foreach (var node in loop)
{
node.Visited = false; // reset visited flag so that we can find outer loops
Debug.Assert(h.Dominates(node) || !node.IsReachable, "The loop body must be dominated by the loop head");
}
ConstructLoop(loop, exitPoint);
}
}
/// <summary> /// Returns the children in a loop dominator tree, with an optional exit point /// Avoids returning continue statements when analysing switches (because increment blocks can be dominated) /// </summary> IEnumerable <ControlFlowNode> DominatorTreeChildren(ControlFlowNode n, ControlFlowNode exitPoint) => n.DominatorTreeChildren.Where(c => c != exitPoint && (!isSwitch || !loopContext.MatchContinue(c)));
/// <summary>
/// Finds a suitable single exit point for the specified loop.
/// </summary>
/// <returns>
/// 1) If a suitable exit point was found: the control flow block that should be reached when breaking from the loop
/// 2) If the loop should not have any exit point (extend by all dominated blocks): NoExitPoint
/// 3) otherwise (exit point unknown, heuristically extend loop): null
/// </returns>
/// <remarks>This method must not write to the Visited flags on the CFG.</remarks>
internal ControlFlowNode FindExitPoint(ControlFlowNode loopHead, IReadOnlyList <ControlFlowNode> naturalLoop)
{
bool hasReachableExit = HasReachableExit(loopHead);
if (!hasReachableExit)
{
// Case 1:
// There are no nodes n so that loopHead dominates a predecessor of n but not n itself
// -> we could build a loop with zero exit points.
if (IsPossibleForeachLoop((Block)loopHead.UserData, out var exitBranch))
{
if (exitBranch != null)
{
// let's see if the target of the exit branch is a suitable exit point
var cfgNode = loopHead.Successors.FirstOrDefault(n => n.UserData == exitBranch.TargetBlock);
if (cfgNode != null && loopHead.Dominates(cfgNode) && !context.ControlFlowGraph.HasReachableExit(cfgNode))
{
return(cfgNode);
}
}
return(NoExitPoint);
}
ControlFlowNode exitPoint = null;
int exitPointILOffset = -1;
ConsiderReturnAsExitPoint((Block)loopHead.UserData, ref exitPoint, ref exitPointILOffset);
foreach (var node in loopHead.DominatorTreeChildren)
{
PickExitPoint(node, ref exitPoint, ref exitPointILOffset);
}
return(exitPoint);
}
else
{
// Case 2:
// We need to pick our exit point so that all paths from the loop head
// to the reachable exits run through that exit point.
var cfg = context.ControlFlowGraph.cfg;
var revCfg = PrepareReverseCFG(loopHead, out int exitNodeArity);
//ControlFlowNode.ExportGraph(cfg).Show("cfg");
//ControlFlowNode.ExportGraph(revCfg).Show("rev");
ControlFlowNode commonAncestor = revCfg[loopHead.UserIndex];
Debug.Assert(commonAncestor.IsReachable);
foreach (ControlFlowNode cfgNode in naturalLoop)
{
ControlFlowNode revNode = revCfg[cfgNode.UserIndex];
if (revNode.IsReachable)
{
commonAncestor = Dominance.FindCommonDominator(commonAncestor, revNode);
}
}
// All paths from within the loop to a reachable exit run through 'commonAncestor'.
// However, this doesn't mean that 'commonAncestor' is valid as an exit point.
// We walk up the post-dominator tree until we've got a valid exit point:
ControlFlowNode exitPoint;
while (commonAncestor.UserIndex >= 0)
{
exitPoint = cfg[commonAncestor.UserIndex];
Debug.Assert(exitPoint.Visited == naturalLoop.Contains(exitPoint));
// It's possible that 'commonAncestor' is itself part of the natural loop.
// If so, it's not a valid exit point.
if (!exitPoint.Visited && ValidateExitPoint(loopHead, exitPoint))
{
// we found an exit point
return(exitPoint);
}
commonAncestor = commonAncestor.ImmediateDominator;
}
// least common post-dominator is the artificial exit node
// This means we're in one of two cases:
// * The loop might have multiple exit points.
// -> we should return null
// * The loop has a single exit point that wasn't considered during post-dominance analysis.
// (which means the single exit isn't dominated by the loop head)
// -> we should return NoExitPoint so that all code dominated by the loop head is included into the loop
if (exitNodeArity > 1)
{
return(null);
}
// Exit node is on the very edge of the tree, and isn't important for determining inclusion
// Still necessary for switch detection to insert correct leave statements
if (exitNodeArity == 1 && isSwitch)
{
return(loopContext.GetBreakTargets(loopHead).Distinct().Single());
}
// If exitNodeArity == 0, we should maybe look test if our exits out of the block container are all compatible?
// but I don't think it hurts to have a bit too much code inside the loop in this rare case.
return(NoExitPoint);
}
}
/// <summary>
/// Constructor.
/// </summary>
/// <param name="cfg">ControlFlowGraph</param>
/// <param name="summary">MethodSummary</param>
/// <param name="loopExitNode">ControlFlowNode</param>
internal LoopHeadControlFlowNode(IGraph <IControlFlowNode> cfg,
MethodSummary summary, ControlFlowNode loopExitNode)
: base(cfg, summary)
{
this.LoopExitNode = loopExitNode;
}
protected virtual bool CanReachModification (ControlFlowNode node, Statement start,
IDictionary<Statement, IList<Node>> modifications)
{
return node.NextStatement != null && node.NextStatement != start &&
modifications.ContainsKey (node.NextStatement);
}
static HashSet <ControlFlowNode> FindLoopContent(HashSet <ControlFlowNode> scope, ControlFlowNode head)
{
HashSet <ControlFlowNode> agenda = new HashSet <ControlFlowNode>();
for (int i = 0; i < head.Incoming.Count; i++)
{
var p = head.Incoming[i].Source;
if (head.Dominates(p))
{
agenda.Add(p);
}
}
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))
{
for (int i = 0; i < addNode.Incoming.Count; i++)
{
agenda.Add(addNode.Incoming[i].Source);
}
}
}
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))
{
for (int i = 0; i < addNode.Outgoing.Count; i++)
{
agenda.Add(addNode.Outgoing[i].Target);
}
}
}
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);
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
IList <ILExpression> cases;
ILLabel[] caseLabels;
ILExpression switchCondition;
ILLabel fallLabel;
// IList<ILExpression> cases; out IList<ILExpression> arg, out ILLabel fallLabel)
// matches a switch statment, not sure how the hell I am going to do this
if (block.MatchLastAndBr(GMCode.Switch, out caseLabels, out cases, out fallLabel))
{
// Debug.Assert(fallLabel == endBlock); // this should be true
switchCondition = cases[0]; // thats the switch arg
cases.RemoveAt(0); // remove the switch condition
// Replace the switch code with ILSwitch
ILSwitch ilSwitch = new ILSwitch()
{
Condition = switchCondition
};
block.Body.RemoveTail(GMCode.Switch, GMCode.B);
block.Body.Add(ilSwitch);
block.Body.Add(new ILExpression(GMCode.B, fallLabel));
result.Add(block);
// Remove the item so that it is not picked up as content
scope.RemoveOrThrow(node);
// 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 <ILExpression>(),
EntryGoto = new ILExpression(GMCode.B, 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);
foreach (var con in FindConditions(content, condTarget))
{
caseBlock.Body.Add(con);
}
// 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(GMCode.LoopOrSwitchBreak, null)
}
});
}
}
if (cases[i].Code != GMCode.DefaultCase)
{
caseBlock.Values.Add(cases[i].Arguments[0]);
}
else
{
caseBlock.Values.Add(new ILExpression(GMCode.DefaultCase, null));
}
}
// 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(GMCode.B, fallLabel)
};
ilSwitch.CaseBlocks.Add(caseBlock);
block.Body.RemoveTail(GMCode.B);
scope.ExceptWith(content);
foreach (var con in FindConditions(content, fallTarget))
{
caseBlock.Body.Add(con);
}
// 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(GMCode.LoopOrSwitchBreak, null)
}
});
}
}
}
// Debug.Assert((block.Body.First() as ILLabel).Name != "L1938");
// Two-way branch
ILLabel trueLabel;
ILLabel falseLabel;
IList <ILExpression> condExprs;
if (block.MatchLastAndBr(GMCode.Bf, out falseLabel, out condExprs, out trueLabel) &&
condExprs[0].Code != GMCode.Pop) // its resolved
{
ILExpression condExpr = condExprs[0];
IList <ILNode> body = block.Body;
// this is a simple condition, skip anything short curiket for now
// Match a condition patern
// Convert the brtrue to ILCondition
ILCondition ilCond = new ILCondition()
{
Condition = condExpr,
TrueBlock = new ILBlock()
{
EntryGoto = new ILExpression(GMCode.B, trueLabel)
},
FalseBlock = new ILBlock()
{
EntryGoto = new ILExpression(GMCode.B, falseLabel)
}
};
block.Body.RemoveTail(GMCode.Bf, GMCode.B);
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);
foreach (var con in FindConditions(content, trueTarget))
{
ilCond.TrueBlock.Body.Add(con);
}
}
if (falseTarget != null && HasSingleEdgeEnteringBlock(falseTarget))
{
HashSet <ControlFlowNode> content = FindDominatedNodes(scope, falseTarget);
scope.ExceptWith(content);
foreach (var con in FindConditions(content, falseTarget))
{
ilCond.FalseBlock.Body.Add(con);
}
}
}
}
// 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);
}
internal AdjacencyCollection(ControlFlowNode <TContents> owner, ControlFlowEdgeType edgeType)
{
EdgeType = edgeType;
Owner = owner ?? throw new ArgumentNullException(nameof(owner));
}
/// <summary> /// Obtains all edges to the provided neighbour, if any. /// </summary> /// <param name="target">The neighbouring node.</param> /// <returns>The edges.</returns> public IEnumerable <ControlFlowEdge <TContents> > GetEdgesToNeighbour(ControlFlowNode <TContents> target) => GetEdges(target);
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);
}
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);
}
private void UpdateScopeStack(ControlFlowNode <TInstruction> node, IndexableStack <ScopeInfo> scopeStack)
{
var activeRegions = node.GetSituatedRegions()
.Reverse()
.ToArray();
int largestPossibleCommonDepth = Math.Min(scopeStack.Count, activeRegions.Length);
// Figure out common region depth.
int commonDepth = 1;
while (commonDepth < largestPossibleCommonDepth)
{
if (scopeStack[commonDepth].Region != activeRegions[commonDepth])
{
break;
}
commonDepth++;
}
// Leave for every left region a scope block.
while (scopeStack.Count > commonDepth)
{
scopeStack.Pop();
}
// Enter for every entered region a new block.
while (scopeStack.Count < activeRegions.Length)
{
// Create new scope block.
var enteredRegion = activeRegions[scopeStack.Count];
// Add new cope block to the current scope.
var currentScope = scopeStack.Peek();
if (enteredRegion is ExceptionHandlerRegion <TInstruction> ehRegion)
{
// We entered an exception handler region.
var ehBlock = new ExceptionHandlerBlock <TInstruction>();
currentScope.AddBlock(ehBlock);
scopeStack.Push(new ScopeInfo(ehRegion, ehBlock));
}
else if (enteredRegion.ParentRegion is ExceptionHandlerRegion <TInstruction> parentEhRegion)
{
// We entered one of the exception handler sub regions. Figure out which one it is.
var enteredBlock = default(ScopeBlock <TInstruction>);
if (!(currentScope.Block is ExceptionHandlerBlock <TInstruction> ehBlock))
{
throw new InvalidOperationException("The parent scope is not an exception handler scope.");
}
if (parentEhRegion.ProtectedRegion == enteredRegion)
{
// We entered the protected region.
enteredBlock = ehBlock.ProtectedBlock;
}
else
{
// We entered a handler region.
enteredBlock = new ScopeBlock <TInstruction>();
ehBlock.HandlerBlocks.Add(enteredBlock);
}
// Push the entered scope.
scopeStack.Push(new ScopeInfo(parentEhRegion.ProtectedRegion, enteredBlock));
}
else
{
// Fall back method: just enter a new scope block.
var scopeBlock = new ScopeBlock <TInstruction>();
currentScope.AddBlock(scopeBlock);
scopeStack.Push(new ScopeInfo(enteredRegion, scopeBlock));
}
}
}
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++, 0xffffffff, ControlFlowNodeType.RegularExit);
cfNodes.Add(regularExit);
ControlFlowNode exceptionalExit = new ControlFlowNode(index++, 0xffffffff, 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++, 0xffffffff, ControlFlowNodeType.Normal);
cfNodes.Add(cfNode);
astNodeToCfNode[node] = cfNode;
cfNode.UserData = node;
// Find all contained labels
foreach (ILLabel label in node.GetSelfAndChildrenRecursive <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];
// Find all branches
foreach (ILLabel target in node.GetSelfAndChildrenRecursive <ILExpression>(e => e.IsBranch()).SelectMany(e => e.GetBranchTargets()))
{
ControlFlowNode destination;
// Labels which are out of out scope will not be in 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 bool MatchContinue(ControlFlowNode node) => MatchContinue(node, out var _);
/// <summary>
/// Constructs a new control flow graph.
/// Each node cfg[i] has a corresponding node rev[i].
/// Edges are only created for nodes dominated by loopHead, and are in reverse from their direction
/// in the primary CFG.
/// An artificial exit node is used for edges that leave the set of nodes dominated by loopHead,
/// or that leave the block Container.
/// </summary>
/// <param name="loopHead">Entry point of the loop.</param>
/// <param name="exitNodeArity">out: The number of different CFG nodes.
/// Possible values:
/// 0 = no CFG nodes used as exit nodes (although edges leaving the block container might still be exits);
/// 1 = a single CFG node (not dominated by loopHead) was used as an exit node;
/// 2 = more than one CFG node (not dominated by loopHead) was used as an exit node.
/// </param>
/// <returns></returns>
ControlFlowNode[] PrepareReverseCFG(ControlFlowNode loopHead, out int exitNodeArity)
{
ControlFlowNode[] cfg = context.ControlFlowGraph.cfg;
ControlFlowNode[] rev = new ControlFlowNode[cfg.Length + 1];
for (int i = 0; i < cfg.Length; i++)
{
rev[i] = new ControlFlowNode {
UserIndex = i, UserData = cfg[i].UserData
};
}
ControlFlowNode nodeTreatedAsExitNode = null;
bool multipleNodesTreatedAsExitNodes = false;
ControlFlowNode exitNode = new ControlFlowNode {
UserIndex = -1
};
rev[cfg.Length] = exitNode;
for (int i = 0; i < cfg.Length; i++)
{
if (!loopHead.Dominates(cfg[i]) || isSwitch && cfg[i] != loopHead && loopContext.MatchContinue(cfg[i]))
{
continue;
}
// Add reverse edges for all edges in cfg
foreach (var succ in cfg[i].Successors)
{
// edges to outer loops still count as exits (labelled continue not implemented)
if (isSwitch && loopContext.MatchContinue(succ, 1))
{
continue;
}
if (loopHead.Dominates(succ))
{
rev[succ.UserIndex].AddEdgeTo(rev[i]);
}
else
{
if (nodeTreatedAsExitNode == null)
{
nodeTreatedAsExitNode = succ;
}
if (nodeTreatedAsExitNode != succ)
{
multipleNodesTreatedAsExitNodes = true;
}
exitNode.AddEdgeTo(rev[i]);
}
}
if (context.ControlFlowGraph.HasDirectExitOutOfContainer(cfg[i]))
{
exitNode.AddEdgeTo(rev[i]);
}
}
if (multipleNodesTreatedAsExitNodes)
{
exitNodeArity = 2; // more than 1
}
else if (nodeTreatedAsExitNode != null)
{
exitNodeArity = 1;
}
else
{
exitNodeArity = 0;
}
Dominance.ComputeDominance(exitNode, context.CancellationToken);
return(rev);
}
public bool MatchContinue(ControlFlowNode node, int depth) => MatchContinue(node, out int _depth) && depth == _depth;
/// <summary>
/// Extension of ControlFlowGraph.HasReachableExit
/// Uses loopContext.GetBreakTargets().Any() when analyzing switches to avoid
/// classifying continue blocks as reachable exits.
/// </summary>
bool HasReachableExit(ControlFlowNode node) => isSwitch
? loopContext.GetBreakTargets(node).Any()
: context.ControlFlowGraph.HasReachableExit(node);
public bool MatchContinue(ControlFlowNode node, out int depth) => continueDepth.TryGetValue(node, out depth);
/// <summary>
/// Finds a suitable single exit point for the specified loop.
/// </summary>
/// <returns>
/// 1) If a suitable exit point was found: the control flow block that should be reached when breaking from the loop
/// 2) If the loop should not have any exit point (extend by all dominated blocks): NoExitPoint
/// 3) otherwise (exit point unknown, heuristically extend loop): null
/// </returns>
/// <remarks>This method must not write to the Visited flags on the CFG.</remarks>
ControlFlowNode FindExitPoint(ControlFlowNode loopHead, IReadOnlyList <ControlFlowNode> naturalLoop, bool treatBackEdgesAsExits)
{
bool hasReachableExit = context.ControlFlowGraph.HasReachableExit(loopHead);
if (!hasReachableExit && treatBackEdgesAsExits)
{
// If we're analyzing the switch, there's no reachable exit, but the loopHead (=switchHead) block
// is also a loop head, we consider the back-edge a reachable exit for the switch.
hasReachableExit = loopHead.Predecessors.Any(p => loopHead.Dominates(p));
}
if (!hasReachableExit)
{
// Case 1:
// There are no nodes n so that loopHead dominates a predecessor of n but not n itself
// -> we could build a loop with zero exit points.
if (IsPossibleForeachLoop((Block)loopHead.UserData, out var exitBranch))
{
if (exitBranch != null)
{
// let's see if the target of the exit branch is a suitable exit point
var cfgNode = loopHead.Successors.FirstOrDefault(n => n.UserData == exitBranch.TargetBlock);
if (cfgNode != null && loopHead.Dominates(cfgNode) && !context.ControlFlowGraph.HasReachableExit(cfgNode))
{
return(cfgNode);
}
}
return(NoExitPoint);
}
ControlFlowNode exitPoint = null;
int exitPointILOffset = -1;
foreach (var node in loopHead.DominatorTreeChildren)
{
PickExitPoint(node, ref exitPoint, ref exitPointILOffset);
}
return(exitPoint);
}
else
{
// Case 2:
// We need to pick our exit point so that all paths from the loop head
// to the reachable exits run through that exit point.
var cfg = context.ControlFlowGraph.cfg;
var revCfg = PrepareReverseCFG(loopHead, treatBackEdgesAsExits);
//ControlFlowNode.ExportGraph(cfg).Show("cfg");
//ControlFlowNode.ExportGraph(revCfg).Show("rev");
ControlFlowNode commonAncestor = revCfg[loopHead.UserIndex];
Debug.Assert(commonAncestor.IsReachable);
foreach (ControlFlowNode cfgNode in naturalLoop)
{
ControlFlowNode revNode = revCfg[cfgNode.UserIndex];
if (revNode.IsReachable)
{
commonAncestor = Dominance.FindCommonDominator(commonAncestor, revNode);
}
}
// All paths from within the loop to a reachable exit run through 'commonAncestor'.
// However, this doesn't mean that 'commonAncestor' is valid as an exit point.
// We walk up the post-dominator tree until we've got a valid exit point:
ControlFlowNode exitPoint;
while (commonAncestor.UserIndex >= 0)
{
exitPoint = cfg[commonAncestor.UserIndex];
Debug.Assert(exitPoint.Visited == naturalLoop.Contains(exitPoint));
// It's possible that 'commonAncestor' is itself part of the natural loop.
// If so, it's not a valid exit point.
if (!exitPoint.Visited && ValidateExitPoint(loopHead, exitPoint))
{
// we found an exit point
return(exitPoint);
}
commonAncestor = commonAncestor.ImmediateDominator;
}
// least common post-dominator is the artificial exit node
return(null);
}
}
public int GetContinueDepth(ControlFlowNode node) => MatchContinue(node, out var depth) ? depth : 0;
/// <summary>
/// This function implements a heuristic algorithm that tries to reduce the number of exit
/// points. It is only used as fall-back when it is impossible to use a single exit point.
/// </summary>
/// <remarks>
/// This heuristic loop extension algorithm traverses the loop head's dominator tree in pre-order.
/// For each candidate node, we detect whether adding it to the loop reduces the number of exit points.
/// If it does, the candidate is added to the loop.
///
/// Adding a node to the loop has two effects on the the number of exit points:
/// * exit points that were added to the loop are no longer exit points, thus reducing the total number of exit points
/// * successors of the newly added nodes might be new, additional exit points
///
/// Requires and maintains the invariant that a node is marked as visited iff it is contained in the loop.
/// </remarks>
void ExtendLoopHeuristic(ControlFlowNode loopHead, List <ControlFlowNode> loop, ControlFlowNode candidate)
{
Debug.Assert(candidate.Visited == loop.Contains(candidate));
if (!candidate.Visited)
{
// This node not yet part of the loop, but might be added
List <ControlFlowNode> additionalNodes = new List <ControlFlowNode>();
// Find additionalNodes nodes and mark them as visited.
candidate.TraversePreOrder(n => n.Predecessors, additionalNodes.Add);
// This means Visited now represents the candiate extended loop.
// Determine new exit points that are reachable from the additional nodes
// (note: some of these might have previously been exit points, too)
var newExitPoints = additionalNodes.SelectMany(n => n.Successors).Where(n => !n.Visited).ToHashSet();
// Make visited represent the unextended loop, so that we can measure the exit points
// in the old state.
foreach (var node in additionalNodes)
{
node.Visited = false;
}
// Measure number of added and removed exit points
int removedExitPoints = additionalNodes.Count(IsExitPoint);
int addedExitPoints = newExitPoints.Count(n => !IsExitPoint(n));
if (removedExitPoints > addedExitPoints)
{
// We can reduce the number of exit points by adding the candidate node to the loop.
candidate.TraversePreOrder(n => n.Predecessors, loop.Add);
}
}
// Pre-order traversal of dominator tree
foreach (var node in candidate.DominatorTreeChildren)
{
ExtendLoopHeuristic(loopHead, loop, node);
}
}
/// <summary> /// Lists all potential targets for break; statements from a domination tree, /// assuming the domination tree must be exited via either break; or continue; /// /// First list all nodes in the dominator tree (excluding continue nodes) /// Then return the all successors not contained within said tree. /// /// Note that node will be returned once for each outgoing edge. /// Labelled continue statements (depth > 1) are counted as break targets /// </summary> internal IEnumerable <ControlFlowNode> GetBreakTargets(ControlFlowNode dominator) => TreeTraversal.PreOrder(dominator, n => n.DominatorTreeChildren.Where(c => !MatchContinue(c))) .SelectMany(n => n.Successors) .Where(n => !dominator.Dominates(n) && !MatchContinue(n, 1));
public ControlFlowLink(Condition condition, ControlFlowNode target)
{
Condition = condition;
Target = target;
}
/// <summary> /// A flow node contains only two instructions, the first of which is an IfInstruction /// A short circuit expression is comprised of a root block ending in an IfInstruction and one or more flow nodes /// </summary> static bool IsFlowNode(ControlFlowNode n) => ((Block)n.UserData).Instructions.FirstOrDefault() is IfInstruction;
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);
}
public void Complex()
{
// Example graph from:
// http://www.sable.mcgill.ca/~hendren/621/ControlFlowAnalysis_Handouts.pdf
// (slide 57)
var cfg = new ControlFlowGraph <int>(IntArchitecture.Instance);
var nodes = new ControlFlowNode <int> [11];
for (int i = 0; i < nodes.Length; i++)
{
nodes[i] = new ControlFlowNode <int>(i, i);
cfg.Nodes.Add(nodes[i]);
}
nodes[0].ConnectWith(nodes[1]);
nodes[1].ConnectWith(nodes[2], ControlFlowEdgeType.Conditional);
nodes[1].ConnectWith(nodes[3]);
nodes[2].ConnectWith(nodes[3]);
nodes[3].ConnectWith(nodes[4]);
nodes[4].ConnectWith(nodes[3], ControlFlowEdgeType.Conditional);
nodes[4].ConnectWith(nodes[5]);
nodes[4].ConnectWith(nodes[6], ControlFlowEdgeType.Conditional);
nodes[5].ConnectWith(nodes[7]);
nodes[6].ConnectWith(nodes[7]);
nodes[7].ConnectWith(nodes[8]);
nodes[7].ConnectWith(nodes[4], ControlFlowEdgeType.Conditional);
nodes[8].ConnectWith(nodes[9]);
nodes[8].ConnectWith(nodes[10], ControlFlowEdgeType.Conditional);
nodes[8].ConnectWith(nodes[3], ControlFlowEdgeType.Conditional);
nodes[9].ConnectWith(nodes[1]);
nodes[10].ConnectWith(nodes[7]);
cfg.Entrypoint = nodes[0];
var tree = DominatorTree.FromGraph(cfg);
Assert.Empty(tree.GetDominanceFrontier(nodes[0]));
Assert.Equal(new HashSet <INode> {
nodes[1]
}, tree.GetDominanceFrontier(nodes[1]));
Assert.Equal(new HashSet <INode> {
nodes[3]
}, tree.GetDominanceFrontier(nodes[2]));
Assert.Equal(new HashSet <INode> {
nodes[1], nodes[3]
}, tree.GetDominanceFrontier(nodes[3]));
Assert.Equal(new HashSet <INode> {
nodes[1], nodes[3], nodes[4]
}, tree.GetDominanceFrontier(nodes[4]));
Assert.Equal(new HashSet <INode> {
nodes[7]
}, tree.GetDominanceFrontier(nodes[5]));
Assert.Equal(new HashSet <INode> {
nodes[7]
}, tree.GetDominanceFrontier(nodes[6]));
Assert.Equal(new HashSet <INode> {
nodes[1], nodes[3], nodes[4], nodes[7]
}, tree.GetDominanceFrontier(nodes[7]));
Assert.Equal(new HashSet <INode> {
nodes[1], nodes[3], nodes[7]
}, tree.GetDominanceFrontier(nodes[8]));
Assert.Equal(new HashSet <INode> {
nodes[1]
}, tree.GetDominanceFrontier(nodes[9]));
Assert.Equal(new HashSet <INode> {
nodes[7]
}, tree.GetDominanceFrontier(nodes[10]));
}
static bool HasSingleEdgeEnteringBlock(ControlFlowNode node)
{
return(node.Incoming.Count(edge => !node.Dominates(edge.Source)) == 1);
}
protected virtual bool CanReachModification(ControlFlowNode node, Statement start,
IDictionary <Statement, IList <Node> > modifications)
{
return(node.NextStatement != null && node.NextStatement != start &&
modifications.ContainsKey(node.NextStatement));
}
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);
}
/// <summary>
/// Constructor.
/// </summary>
/// <param name="cfg">ControlFlowGraph</param>
/// <param name="summary">MethodSummary</param>
/// <param name="loopExitNode">ControlFlowNode</param>
internal LoopHeadControlFlowNode(IGraph<IControlFlowNode> cfg,
MethodSummary summary, ControlFlowNode loopExitNode)
: base(cfg, summary)
{
this.LoopExitNode = loopExitNode;
}
