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@ -73,9 +73,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
@@ -73,9 +73,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
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n.Successors.ForEach(Analyze); |
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} |
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contextNode.Successors.ForEach(Analyze); |
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foreach (var node in cfg.cfg) |
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node.Visited = false; |
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ResetVisited(cfg.cfg); |
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int l = 1; |
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foreach (var loopHead in loopHeads.OrderBy(n => n.PostOrderNumber)) |
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@ -286,15 +284,19 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
@@ -286,15 +284,19 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
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// good enough indicator that the surrounding code also forms a switch statement
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if (analysis.ContainsILSwitch || MatchRoslynSwitchOnString()) |
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return true; |
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// heuristic to determine if a block would be better represented as an if statement rather than switch
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int ifCount = analysis.InnerBlocks.Count + 1; |
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int labelCount = analysis.Sections.Where(s => !s.Key.SetEquals(defaultSectionKey)).Sum(s => s.Key.Intervals.Length); |
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// heuristic to determine if a block would be better represented as an if statement rather than a case statement
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if (ifCount < labelCount) |
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int intervalCount = analysis.Sections.Where(s => !s.Key.SetEquals(defaultSectionKey)).Sum(s => s.Key.Intervals.Length); |
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if (ifCount < intervalCount) |
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return false; |
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(var flowNodes, var caseNodes) = AnalyzeControlFlow(); |
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// don't create switch statements with only one non-default label (provided the if option is short enough)
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if (analysis.Sections.Count == 2 && ifCount <= 2) |
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// don't create switch statements with only one non-default label when the corresponding condition tree is flat
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// it may be important that the switch-like conditions be inlined
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// for example, a loop condition: while (c == '\n' || c == '\r')
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if (analysis.Sections.Count == 2 && IsSingleCondition(flowNodes, caseNodes)) |
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return false; |
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// if there is no ILSwitch, there's still many control flow patterns that
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@ -305,9 +307,10 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
@@ -305,9 +307,10 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
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// These goto statements may be "goto case x" or "goto default", but these are a hint that the original code was not a switch,
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// and that the switch statement may be very poor quality.
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// Thus the rule of thumb is no goto statements if the original code didn't include them
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if (SwitchUsesGoto(out var breakBlock)) |
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if (SwitchUsesGoto(flowNodes, caseNodes, out var breakBlock)) |
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return false; |
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// valid switch construction, all code can be inlined
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if (breakBlock == null) |
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return true; |
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@ -318,10 +321,6 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
@@ -318,10 +321,6 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
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/// <summary>
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/// stloc switchValueVar(call ComputeStringHash(switchValue))
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///
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/// Previously, the roslyn case block heads were added to the flowBlocks for case control flow analysis.
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/// This forbade goto case statements (as is the purpose of ValidatePotentialSwitchFlow)
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/// Identifying the roslyn string switch head is a better indicator for UseCSharpSwitch
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/// </summary>
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private bool MatchRoslynSwitchOnString() |
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{ |
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@ -330,9 +329,10 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
@@ -330,9 +329,10 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
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} |
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/// <summary>
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/// Determines if the analysed switch can be constructed without any gotos
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/// Builds the control flow graph for the current container (if necessary), establishes loopContext
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/// and returns the ControlFlowNodes corresponding to the inner flow and case blocks of the potential switch
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/// </summary>
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private bool SwitchUsesGoto(out Block breakBlock) |
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private (List<ControlFlowNode> flowNodes, List<ControlFlowNode> caseNodes) AnalyzeControlFlow() |
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{ |
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if (controlFlowGraph == null) |
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controlFlowGraph = new ControlFlowGraph(currentContainer, context.CancellationToken); |
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@ -340,6 +340,9 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
@@ -340,6 +340,9 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
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var switchHead = controlFlowGraph.GetNode(analysis.RootBlock); |
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loopContext = new LoopContext(controlFlowGraph, switchHead); |
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var flowNodes = new List<ControlFlowNode> { switchHead }; |
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flowNodes.AddRange(analysis.InnerBlocks.Select(controlFlowGraph.GetNode)); |
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// grab the control flow nodes for blocks targetted by each section
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var caseNodes = new List<ControlFlowNode>(); |
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foreach (var s in analysis.Sections) { |
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@ -351,13 +354,22 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
@@ -351,13 +354,22 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
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caseNodes.Add(node); |
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} |
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var flowBlocks = analysis.InnerBlocks.ToHashSet(); |
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flowBlocks.Add(analysis.RootBlock); |
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AddNullCase(flowBlocks, caseNodes); |
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AddNullCase(flowNodes, caseNodes); |
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Debug.Assert(flowNodes.SelectMany(n => n.Successors) |
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.All(n => flowNodes.Contains(n) || caseNodes.Contains(n) || loopContext.MatchContinue(n))); |
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return (flowNodes, caseNodes); |
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} |
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/// <summary>
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/// Determines if the analysed switch can be constructed without any gotos
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/// </summary>
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private bool SwitchUsesGoto(List<ControlFlowNode> flowNodes, List<ControlFlowNode> caseNodes, out Block breakBlock) |
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{ |
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// cases with predecessors that aren't part of the switch logic
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// must either require "goto case" statements, or consist of a single "break;"
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var externalCases = caseNodes.Where(c => c.Predecessors.Any(n => !flowBlocks.Contains(n.UserData))).ToList(); |
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var externalCases = caseNodes.Where(c => c.Predecessors.Any(n => !flowNodes.Contains(n))).ToList(); |
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breakBlock = null; |
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if (externalCases.Count > 1) |
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@ -381,7 +393,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
@@ -381,7 +393,7 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
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/// Does some of the analysis of SwitchOnNullableTransform to add the null case control flow
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/// to the results of SwitchAnaylsis
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/// </summary>
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private void AddNullCase(HashSet<Block> flowBlocks, List<ControlFlowNode> caseNodes) |
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private void AddNullCase(List<ControlFlowNode> flowNodes, List<ControlFlowNode> caseNodes) |
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{ |
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if (analysis.RootBlock.IncomingEdgeCount != 1) |
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return; |
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@ -406,7 +418,94 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
@@ -406,7 +418,94 @@ namespace ICSharpCode.Decompiler.IL.ControlFlow
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return; |
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//add the null case logic to the incoming flow blocks
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flowBlocks.Add(nullableBlock); |
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flowNodes.Add(controlFlowGraph.GetNode(nullableBlock)); |
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} |
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/// <summary>
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/// Pattern matching for short circuit expressions
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/// p
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/// |\
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/// | n
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/// |/ \
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/// s c
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///
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/// where
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/// p: if (a) goto n; goto s;
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/// n: if (b) goto c; goto s;
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///
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/// Can simplify to
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/// p|n
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/// / \
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/// s c
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///
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/// where:
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/// p|n: if (a && b) goto c; goto s;
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///
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/// Note that if n has only 1 successor, but is still a flow node, then a short circuit expression
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/// has a target (c) with no corresponding block (leave)
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/// </summary>
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/// <param name="parent">A node with 2 successors</param>
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/// <param name="side">The successor index to consider n (the other successor will be the common sibling)</param>
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private static bool IsShortCircuit(ControlFlowNode parent, int side) |
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{ |
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var node = parent.Successors[side]; |
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var sibling = parent.Successors[side ^ 1]; |
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if (!IsFlowNode(node) || node.Successors.Count > 2 || node.Predecessors.Count != 1) |
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return false; |
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return node.Successors.Contains(sibling); |
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} |
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/// <summary>
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/// A flow node contains only two instructions, the first of which is an IfInstruction
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/// A short circuit expression is comprised of a root block ending in an IfInstruction and one or more flow nodes
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/// </summary>
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static bool IsFlowNode(ControlFlowNode n) => ((Block)n.UserData).Instructions.FirstOrDefault() is IfInstruction; |
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/// <summary>
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/// Determines whether the flowNodes are can be reduced to a single condition via short circuit operators
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/// </summary>
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private bool IsSingleCondition(List<ControlFlowNode> flowNodes, List<ControlFlowNode> caseNodes) |
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{ |
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if (flowNodes.Count == 1) |
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return true; |
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var rootNode = controlFlowGraph.GetNode(analysis.RootBlock); |
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rootNode.Visited = true; |
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// search down the tree, marking nodes as visited while they continue the current condition
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var n = rootNode; |
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while (n.Successors.Count > 0 && (n == rootNode || IsFlowNode(n))) { |
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if (n.Successors.Count == 1) { |
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// if there is more than one case node, then a flow node with only one successor is not part of the initial condition
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if (caseNodes.Count > 1) |
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break; |
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n = n.Successors[0]; |
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} |
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else { // 2 successors
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if (IsShortCircuit(n, 0)) |
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n = n.Successors[0]; |
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else if (IsShortCircuit(n, 1)) |
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n = n.Successors[1]; |
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else |
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break; |
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} |
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n.Visited = true; |
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if (loopContext.MatchContinue(n)) |
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break; |
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} |
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var ret = flowNodes.All(f => f.Visited); |
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ResetVisited(controlFlowGraph.cfg); |
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return ret; |
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} |
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private static void ResetVisited(IEnumerable<ControlFlowNode> nodes) |
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{ |
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foreach (var n in nodes) |
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n.Visited = false; |
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} |
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} |
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} |
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Chicken-Bones
7 years ago