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…tionDetection, only transform to fall-through block-exit at the end of the transform pipeline. This fixes an issue where `return` statements within try-blocks could turn into `goto` statements.
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185 changes: 185 additions & 0 deletions
185
ICSharpCode.Decompiler/IL/ControlFlow/RemoveRedundantReturn.cs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,185 @@ | ||
| // Copyright (c) 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.Diagnostics; | ||
| using System.Linq; | ||
|
|
||
| using ICSharpCode.Decompiler.IL.Transforms; | ||
|
|
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| namespace ICSharpCode.Decompiler.IL.ControlFlow | ||
| { | ||
| /// <summary> | ||
| /// Similar to <see cref="DetectExitPoints"/>, but acts only on <c>leave</c> instructions | ||
| /// leaving the whole function (<c>return</c>/<c>yield break</c>) that can be made implicit | ||
| /// without using goto. | ||
| /// </summary> | ||
| class RemoveRedundantReturn : IILTransform | ||
| { | ||
| public void Run(ILFunction function, ILTransformContext context) | ||
| { | ||
| foreach (var lambda in function.Descendants.OfType<ILFunction>()) | ||
| { | ||
| if (lambda.Body is BlockContainer c && ((lambda.AsyncReturnType ?? lambda.ReturnType).Kind == TypeSystem.TypeKind.Void || lambda.IsIterator)) | ||
| { | ||
| Block lastBlock = c.Blocks.Last(); | ||
| if (lastBlock.Instructions.Last() is Leave { IsLeavingFunction: true }) | ||
| { | ||
| ConvertReturnToFallthrough(lastBlock.Instructions.SecondToLastOrDefault()); | ||
| } | ||
| else | ||
| { | ||
| if (ConvertReturnToFallthrough(lastBlock.Instructions.Last())) | ||
| { | ||
| lastBlock.Instructions.Add(new Leave(c)); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| private static bool ConvertReturnToFallthrough(ILInstruction? inst) | ||
| { | ||
| bool result = false; | ||
| switch (inst) | ||
| { | ||
| case BlockContainer c: | ||
| if (c.Kind != ContainerKind.Normal) | ||
| { | ||
| // loop or switch: turn all "return" into "break" | ||
| result |= ReturnToLeaveInContainer(c); | ||
| } | ||
| else | ||
| { | ||
| // body of try block, or similar: recurse into last instruction in container | ||
| Block lastBlock = c.Blocks.Last(); | ||
| if (lastBlock.Instructions.Last() is Leave { IsLeavingFunction: true, Value: Nop } leave) | ||
| { | ||
| leave.TargetContainer = c; | ||
| result = true; | ||
| } | ||
| else if (ConvertReturnToFallthrough(lastBlock.Instructions.Last())) | ||
| { | ||
| lastBlock.Instructions.Add(new Leave(c)); | ||
| result = true; | ||
| } | ||
| } | ||
| break; | ||
| case TryCatch tryCatch: | ||
| result |= ConvertReturnToFallthrough(tryCatch.TryBlock); | ||
| foreach (var h in tryCatch.Handlers) | ||
| { | ||
| result |= ConvertReturnToFallthrough(h.Body); | ||
| } | ||
| break; | ||
| case TryFinally tryFinally: | ||
| result |= ConvertReturnToFallthrough(tryFinally.TryBlock); | ||
| break; | ||
| case LockInstruction lockInst: | ||
| result |= ConvertReturnToFallthrough(lockInst.Body); | ||
| break; | ||
| case UsingInstruction usingInst: | ||
| result |= ConvertReturnToFallthrough(usingInst.Body); | ||
| break; | ||
| case PinnedRegion pinnedRegion: | ||
| result |= ConvertReturnToFallthrough(pinnedRegion.Body); | ||
| break; | ||
| case IfInstruction ifInstruction: | ||
| result |= ConvertReturnToFallthrough(ifInstruction.TrueInst); | ||
| result |= ConvertReturnToFallthrough(ifInstruction.FalseInst); | ||
| break; | ||
| case Block block when block.Kind == BlockKind.ControlFlow: | ||
| { | ||
| var lastInst = block.Instructions.LastOrDefault(); | ||
| if (lastInst is Leave { IsLeavingFunction: true, Value: Nop }) | ||
| { | ||
| block.Instructions.RemoveAt(block.Instructions.Count - 1); | ||
| result = true; | ||
| lastInst = block.Instructions.LastOrDefault(); | ||
| } | ||
| result |= ConvertReturnToFallthrough(lastInst); | ||
| break; | ||
| } | ||
| } | ||
| return result; | ||
| } | ||
|
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||
| /// <summary> | ||
| /// Transforms | ||
| /// loop { ... if (x) return; .. } | ||
| /// to | ||
| /// loop { ... if (x) break; .. } return; | ||
| /// </summary> | ||
| internal static void ReturnToBreak(Block parentBlock, BlockContainer loopOrSwitch, ILTransformContext context) | ||
| { | ||
| Debug.Assert(loopOrSwitch.Parent == parentBlock); | ||
| // This transform is only possible when the loop/switch doesn't already use "break;" | ||
| if (loopOrSwitch.LeaveCount != 0) | ||
| return; | ||
| // loopOrSwitch with LeaveCount==0 has unreachable exit point and thus must be last in block. | ||
| Debug.Assert(parentBlock.Instructions.Last() == loopOrSwitch); | ||
| var nearestFunction = parentBlock.Ancestors.OfType<ILFunction>().First(); | ||
| if (nearestFunction.Body is BlockContainer functionContainer) | ||
| { | ||
| context.Step("pull return out of loop/switch: " + loopOrSwitch.EntryPoint.Label, loopOrSwitch); | ||
| if (ReturnToLeaveInContainer(loopOrSwitch)) | ||
| { | ||
| // insert a return after the loop | ||
| parentBlock.Instructions.Add(new Leave(functionContainer)); | ||
| } | ||
| } | ||
| } | ||
|
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| private static bool ReturnToLeaveInContainer(BlockContainer c) | ||
| { | ||
| bool result = false; | ||
| foreach (var block in c.Blocks) | ||
| { | ||
| result |= ReturnToLeave(block, c); | ||
| } | ||
| return result; | ||
| } | ||
|
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| private static bool ReturnToLeave(ILInstruction inst, BlockContainer c) | ||
| { | ||
| if (inst is Leave { IsLeavingFunction: true, Value: Nop } leave) | ||
| { | ||
| leave.TargetContainer = c; | ||
| return true; | ||
| } | ||
| else if (inst is BlockContainer nested && nested.Kind != ContainerKind.Normal) | ||
| { | ||
| return false; | ||
| } | ||
| else if (inst is ILFunction) | ||
| { | ||
| return false; | ||
| } | ||
| else | ||
| { | ||
| bool b = false; | ||
| foreach (var child in inst.Children) | ||
| { | ||
| b |= ReturnToLeave(child, c); | ||
| } | ||
| return b; | ||
| } | ||
| } | ||
| } | ||
| } |
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