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 = null;
ILLabel trueLabel;
ILLabel falseLabel;
// It has to be just brtrue - any preceding code would introduce goto
error.Assert(!basicBlock.MatchLastAndBr(GMCode.Bt, out trueLabel, out condExpr, out falseLabel),
"Unrolled loop");
if (basicBlock.MatchLastAndBr(GMCode.Bt, out trueLabel, out condExpr, out falseLabel) ||
basicBlock.MatchLastAndBr(GMCode.Pushenv, out falseLabel, out condExpr, out trueLabel) || // built it the same way from the dissasembler, this needs inverted
basicBlock.MatchLastAndBr(GMCode.Repeat, out trueLabel, out condExpr, out falseLabel)) // repeate loop is built like a while
{
GMCode loopType = (basicBlock.Body.ElementAt(basicBlock.Body.Count - 2) as ILExpression).Code;
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);
bool mustNegate = false;
if (loopContents.Contains(falseTarget) || falseTarget == node)
{
// Negate the condition
mustNegate = true;
// condExpr = new ILExpression(GMCode.Not, null, condExpr);
ILLabel tmp = trueLabel;
trueLabel = falseLabel;
falseLabel = tmp;
}
// HACK
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);
}
//Debug.Assert(false);
Debug.Assert(condExpr != null);
switch (loopType)
{
case GMCode.Pushenv:
basicBlock.Body.RemoveTail(GMCode.Pushenv, GMCode.B);
basicBlock.Body.Add(new ILWithStatement()
{
Condition = condExpr, // we never negate
Body = new ILBlock()
{
EntryGoto = new ILExpression(GMCode.B, trueLabel),
Body = FindLoops(loopContents, node, false)
}
});
break;
case GMCode.Bt:
basicBlock.Body.RemoveTail(GMCode.Bt, GMCode.B);
basicBlock.Body.Add(new ILWhileLoop()
{
Condition = mustNegate ? condExpr.NegateCondition() : condExpr,
Body = new ILBlock()
{
EntryGoto = new ILExpression(GMCode.B, trueLabel),
Body = FindLoops(loopContents, node, false)
}
});
break;
case GMCode.Repeat:
basicBlock.Body.RemoveTail(GMCode.Repeat, GMCode.B);
basicBlock.Body.Add(new ILRepeat()
{
Condition = condExpr, // we never negate
Body = new ILBlock()
{
EntryGoto = new ILExpression(GMCode.B, trueLabel),
Body = FindLoops(loopContents, node, false)
}
});
break;
}
basicBlock.Body.Add(new ILExpression(GMCode.B, falseLabel));
result.Add(basicBlock);
scope.ExceptWith(loopContents);
}
}
// Fallback method: while(true)
if (scope.Contains(node))
{
Debug.Assert(false);
result.Add(new ILBasicBlock()
{
Body = new List <ILNode>()
{
ILLabel.Generate("Loop"),
new ILWhileLoop()
{
Condition = new ILExpression(GMCode.Constant, new ILValue(true)),
Body = new ILBlock()
{
EntryGoto = new ILExpression(GMCode.B, (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);
}
