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Fix #3075: eliminate recursion in TopologicalSort and BlockTransform.
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,115 @@ | ||
| // Copyright (c) 2023 Daniel Grunwald | ||
| // | ||
| // Permission is hereby granted, free of charge, to any person obtaining a copy of this | ||
| // software and associated documentation files (the "Software"), to deal in the Software | ||
| // without restriction, including without limitation the rights to use, copy, modify, merge, | ||
| // publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons | ||
| // to whom the Software is furnished to do so, subject to the following conditions: | ||
| // | ||
| // The above copyright notice and this permission notice shall be included in all copies or | ||
| // substantial portions of the Software. | ||
| // | ||
| // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, | ||
| // INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR | ||
| // PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE | ||
| // FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR | ||
| // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER | ||
| // DEALINGS IN THE SOFTWARE. | ||
|
|
||
| #nullable enable | ||
|
|
||
| using System; | ||
| using System.Collections.Generic; | ||
|
|
||
| namespace ICSharpCode.Decompiler.Util; | ||
|
|
||
| static class GraphTraversal | ||
| { | ||
| /// <summary> | ||
| /// Depth-first-search of an graph data structure. | ||
| /// The two callbacks (successorFunc + postorderAction) will be called exactly once for each node reachable from startNodes. | ||
| /// </summary> | ||
| /// <param name="startNodes">The start nodes.</param> | ||
| /// <param name="visitedFunc">Called multiple times per node. The first call should return true, subsequent calls must return false. | ||
| /// If this function is not provided, normal Equals/GetHashCode will be used to compare nodes.</param> | ||
| /// <param name="successorFunc">The function that gets the successors of an element. Called in pre-order.</param> | ||
| /// <param name="postorderAction">Called in post-order.</param> | ||
| /// <param name="reverseSuccessors"> | ||
| /// With reverse_successors=True, the start_nodes and each list of successors will be handled in reverse order. | ||
| /// This is useful if the post-order will be reversed later (e.g. for a topological sort) | ||
| /// so that blocks which could be output in either order (e.g. then-block and else-block of an if) | ||
| /// will maintain the order of the edges (then-block before else-block). | ||
| /// </param> | ||
| public static void DepthFirstSearch<T>(IEnumerable<T> startNodes, Func<T, IEnumerable<T>?> successorFunc, Action<T> postorderAction, Func<T, bool>? visitedFunc = null, bool reverseSuccessors = false) | ||
| { | ||
| /* | ||
| Pseudocode: | ||
| def dfs_walk(start_nodes, successor_func, visited, postorder_func, reverse_successors): | ||
| if reverse_successors: | ||
| start_nodes = reversed(start_nodes) | ||
| for node in start_nodes: | ||
| if node in visited: continue | ||
| visited.insert(node) | ||
| children = successor_func(node) | ||
| dfs_walk(children, successor_func, visited, postorder_action, reverse_successors) | ||
| postorder_action(node) | ||
| The actual implementation here is equivalent but does not use recursion, | ||
| so that we don't blow the stack on large graphs. | ||
| A single stack holds the "continuations" of work that needs to be done. | ||
| These can be either "visit continuations" (=execute the body of the pseudocode | ||
| loop for the given node) or "postorder continuations" (=execute postorder_action) | ||
| */ | ||
| // Use a List as stack (but allowing for the Reverse() usage) | ||
| var worklist = new List<(T node, bool isPostOrderContinuation)>(); | ||
| visitedFunc ??= new HashSet<T>().Add; | ||
| foreach (T node in startNodes) | ||
| { | ||
| worklist.Add((node, false)); | ||
| } | ||
| if (!reverseSuccessors) | ||
| { | ||
| // Our use of a stack will reverse the order of the nodes. | ||
| // If that's not desired, restore original order by reversing twice. | ||
| worklist.Reverse(); | ||
| } | ||
| // Process outstanding continuations: | ||
| while (worklist.Count > 0) | ||
| { | ||
| var (node, isPostOrderContinuation) = worklist.Last(); | ||
| if (isPostOrderContinuation) | ||
| { | ||
| // Execute postorder_action | ||
| postorderAction(node); | ||
| worklist.RemoveAt(worklist.Count - 1); | ||
| continue; | ||
| } | ||
| // Execute body of loop | ||
| if (!visitedFunc(node)) | ||
| { | ||
| // Already visited | ||
| worklist.RemoveAt(worklist.Count - 1); | ||
| continue; | ||
| } | ||
| // foreach-loop-iteration will end with postorder_func call, | ||
| // so switch the type of continuation for this node | ||
| int oldWorkListSize = worklist.Count; | ||
| worklist[oldWorkListSize - 1] = (node, true); | ||
| // Create "visit continuations" for all successor nodes: | ||
| IEnumerable<T>? children = successorFunc(node); | ||
| if (children != null) | ||
| { | ||
| foreach (T child in children) | ||
| { | ||
| worklist.Add((child, false)); | ||
| } | ||
| } | ||
| // Our use of a stack will reverse the order of the nodes. | ||
| // If that's not desired, restore original order by reversing twice. | ||
| if (!reverseSuccessors) | ||
| { | ||
| worklist.Reverse(oldWorkListSize, worklist.Count - oldWorkListSize); | ||
| } | ||
| } | ||
| } | ||
| } |