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94 lines
3.5 KiB
94 lines
3.5 KiB
// Copyright (c) 2014 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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#nullable enable
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using System.Linq;
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using ICSharpCode.Decompiler.Util;
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namespace ICSharpCode.Decompiler.IL
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{
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static class SemanticHelper
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{
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internal static InstructionFlags CombineBranches(InstructionFlags trueFlags, InstructionFlags falseFlags)
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{
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// the endpoint of the 'if' is only unreachable if both branches have an unreachable endpoint
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const InstructionFlags combineWithAnd = InstructionFlags.EndPointUnreachable;
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return (trueFlags & falseFlags) | ((trueFlags | falseFlags) & ~combineWithAnd);
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}
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/// <summary>
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/// Gets whether instruction is pure:
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/// * must not have side effects
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/// * must not throw exceptions
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/// * must not branch
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/// </summary>
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internal static bool IsPure(InstructionFlags inst)
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{
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// ControlFlow is fine: internal control flow is pure as long as it's not an infinite loop,
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// and infinite loops are impossible without MayBranch.
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const InstructionFlags pureFlags = InstructionFlags.MayReadLocals | InstructionFlags.ControlFlow;
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return (inst & ~pureFlags) == 0;
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}
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/// <summary>
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/// Gets whether the instruction sequence 'inst1; inst2;' may be ordered to 'inst2; inst1;'
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/// </summary>
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internal static bool MayReorder(ILInstruction inst1, ILInstruction inst2)
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{
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// If both instructions perform an impure action, we cannot reorder them
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if (!IsPure(inst1.Flags) && !IsPure(inst2.Flags))
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return false;
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// We cannot reorder if inst2 might write what inst1 looks at
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if (Inst2MightWriteToVariableReadByInst1(inst1, inst2))
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return false;
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// and the same in reverse:
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if (Inst2MightWriteToVariableReadByInst1(inst2, inst1))
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return false;
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return true;
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}
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static bool Inst2MightWriteToVariableReadByInst1(ILInstruction inst1, ILInstruction inst2)
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{
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if (!inst1.HasFlag(InstructionFlags.MayReadLocals))
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{
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// quick exit if inst1 doesn't read any variables
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return false;
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}
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var variables = inst1.Descendants.OfType<LdLoc>().Select(load => load.Variable).ToHashSet();
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if (inst2.HasFlag(InstructionFlags.SideEffect) && variables.Any(v => v.AddressCount > 0))
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{
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// If inst2 might have indirect writes, we cannot reorder with any loads of variables that have their address taken.
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return true;
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}
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foreach (var inst in inst2.Descendants)
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{
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if (inst.HasDirectFlag(InstructionFlags.MayWriteLocals))
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{
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ILVariable v = ((IInstructionWithVariableOperand)inst).Variable;
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if (variables.Contains(v))
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{
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return true;
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}
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}
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}
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return false;
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}
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}
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}
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