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118 lines
4.4 KiB
118 lines
4.4 KiB
// Copyright (c) 2016 Daniel Grunwald
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy of this
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// software and associated documentation files (the "Software"), to deal in the Software
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// without restriction, including without limitation the rights to use, copy, modify, merge,
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// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
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// to whom the Software is furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in all copies or
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// substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
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// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
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// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
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// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
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// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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// DEALINGS IN THE SOFTWARE.
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using System.Collections.Generic;
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using System.Linq;
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using ICSharpCode.Decompiler.FlowAnalysis;
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using ICSharpCode.Decompiler.TypeSystem;
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namespace ICSharpCode.Decompiler.IL.Transforms
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{
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/// <summary>
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/// Remove <c>HasInitialValue</c> from locals that are definitely assigned before every use
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/// (=the initial value is a dead store).
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///
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/// In yield return generators, additionally removes dead 'V = null;' assignments.
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///
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/// Additionally infers IType of stack slots that have StackType.Ref
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/// </summary>
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public class RemoveDeadVariableInit : IILTransform
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{
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public void Run(ILFunction function, ILTransformContext context)
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{
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ResetHasInitialValueFlag(function, context);
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// Remove dead stores to variables that are never read from.
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// If the stored value has some side-effect, the value is unwrapped.
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// This is necessary to remove useless stores generated by some compilers, e.g., the F# compiler.
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// In yield return + async, the C# compiler tends to store null/default(T) to variables
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// when the variable goes out of scope.
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if (function.IsAsync || function.IsIterator || context.Settings.RemoveDeadStores)
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{
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var variableQueue = new Queue<ILVariable>(function.Variables);
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while (variableQueue.Count > 0)
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{
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var v = variableQueue.Dequeue();
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if (v.Kind != VariableKind.Local && v.Kind != VariableKind.StackSlot)
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continue;
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// Skip variables that are captured in a mcs yield state-machine
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// loads of these will only be visible after DelegateConstruction step.
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if (function.StateMachineCompiledWithMono && v.StateMachineField != null)
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continue;
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if (v.LoadCount != 0 || v.AddressCount != 0)
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continue;
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foreach (var stloc in v.StoreInstructions.OfType<StLoc>().ToArray())
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{
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if (stloc.Parent is Block block)
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{
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if (SemanticHelper.IsPure(stloc.Value.Flags))
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{
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block.Instructions.Remove(stloc);
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}
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else
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{
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stloc.ReplaceWith(stloc.Value);
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}
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if (stloc.Value is LdLoc ldloc)
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{
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variableQueue.Enqueue(ldloc.Variable);
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}
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}
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}
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}
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}
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// Try to infer IType of stack slots that are of StackType.Ref:
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foreach (var v in function.Variables)
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{
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if (v.Kind == VariableKind.StackSlot && v.StackType == StackType.Ref && v.AddressCount == 0)
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{
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IType newType = null;
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// Multiple store are possible in case of (c ? ref a : ref b) += 1, for example.
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foreach (var stloc in v.StoreInstructions.OfType<StLoc>())
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{
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var inferredType = stloc.Value.InferType(context.TypeSystem);
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// cancel, if types of values do not match exactly
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if (newType != null && !newType.Equals(inferredType))
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{
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newType = SpecialType.UnknownType;
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break;
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}
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newType = inferredType;
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}
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// Only overwrite existing type, if a "better" type was found.
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if (newType != null && newType != SpecialType.UnknownType)
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v.Type = newType;
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}
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}
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}
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internal static void ResetHasInitialValueFlag(ILFunction function, ILTransformContext context)
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{
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var visitor = new DefiniteAssignmentVisitor(function, context.CancellationToken);
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function.AcceptVisitor(visitor);
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foreach (var v in function.Variables)
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{
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if (v.Kind != VariableKind.Parameter && !visitor.IsPotentiallyUsedUninitialized(v))
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{
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v.HasInitialValue = false;
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}
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}
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}
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}
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}
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