Ejemplo n.º 1
0
        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);
        }