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199 lines
7.7 KiB
199 lines
7.7 KiB
// Copyright (c) 2017 Siegfried Pammer
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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;
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using System.Collections.Generic;
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using System.Linq;
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using ICSharpCode.Decompiler.IL.ControlFlow;
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using ICSharpCode.Decompiler.TypeSystem;
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using ICSharpCode.Decompiler.Util;
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namespace ICSharpCode.Decompiler.IL.Transforms
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{
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/// <summary>
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/// Detects switch-on-nullable patterns employed by the C# compiler and transforms them to an ILAst-switch-instruction.
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/// </summary>
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public class SwitchOnNullableTransform : IILTransform
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{
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public void Run(ILFunction function, ILTransformContext context)
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{
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if (!context.Settings.LiftNullables)
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return;
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HashSet<BlockContainer> changedContainers = new HashSet<BlockContainer>();
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foreach (var block in function.Descendants.OfType<Block>())
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{
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bool changed = false;
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for (int i = block.Instructions.Count - 1; i >= 0; i--)
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{
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SwitchInstruction newSwitch;
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if (MatchSwitchOnNullable(block.Instructions, i, out newSwitch))
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{
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newSwitch.AddILRange(block.Instructions[i - 2]);
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block.Instructions[i + 1].ReplaceWith(newSwitch);
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block.Instructions.RemoveRange(i - 2, 3);
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i -= 2;
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changed = true;
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continue;
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}
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if (MatchRoslynSwitchOnNullable(block.Instructions, i, out newSwitch))
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{
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newSwitch.AddILRange(block.Instructions[i]);
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newSwitch.AddILRange(block.Instructions[i + 1]);
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block.Instructions[i].ReplaceWith(newSwitch);
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block.Instructions.RemoveAt(i + 1);
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changed = true;
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continue;
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}
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}
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if (!changed)
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continue;
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SwitchDetection.SimplifySwitchInstruction(block, context);
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if (block.Parent is BlockContainer container)
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changedContainers.Add(container);
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}
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foreach (var container in changedContainers)
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container.SortBlocks(deleteUnreachableBlocks: true);
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}
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/// <summary>
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/// Matches legacy C# switch on nullable.
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/// </summary>
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bool MatchSwitchOnNullable(InstructionCollection<ILInstruction> instructions, int i, out SwitchInstruction newSwitch)
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{
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newSwitch = null;
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// match first block:
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// stloc tmp(ldloca switchValueVar)
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// stloc switchVariable(call GetValueOrDefault(ldloc tmp))
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// if (logic.not(call get_HasValue(ldloc tmp))) br nullCaseBlock
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// br switchBlock
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if (i < 2)
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return false;
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if (!instructions[i - 2].MatchStLoc(out var tmp, out var ldloca) ||
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!instructions[i - 1].MatchStLoc(out var switchVariable, out var getValueOrDefault) ||
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!instructions[i].MatchIfInstruction(out var condition, out var trueInst))
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return false;
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if (!tmp.IsSingleDefinition || tmp.LoadCount != 2)
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return false;
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if (!switchVariable.IsSingleDefinition || switchVariable.LoadCount != 1)
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return false;
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if (!instructions[i + 1].MatchBranch(out var switchBlock) || !trueInst.MatchBranch(out var nullCaseBlock))
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return false;
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if (!ldloca.MatchLdLoca(out var switchValueVar))
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return false;
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if (!condition.MatchLogicNot(out var getHasValue))
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return false;
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if (!NullableLiftingTransform.MatchGetValueOrDefault(getValueOrDefault, out ILInstruction getValueOrDefaultArg))
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return false;
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if (!NullableLiftingTransform.MatchHasValueCall(getHasValue, out ILInstruction getHasValueArg))
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return false;
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if (!(getHasValueArg.MatchLdLoc(tmp) && getValueOrDefaultArg.MatchLdLoc(tmp)))
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return false;
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// match second block: switchBlock
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// switch (ldloc switchVariable) {
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// case [0..1): br caseBlock1
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// ... more cases ...
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// case [long.MinValue..0),[1..5),[6..10),[11..long.MaxValue]: br defaultBlock
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// }
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if (switchBlock.Instructions.Count != 1 || switchBlock.IncomingEdgeCount != 1)
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return false;
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if (!(switchBlock.Instructions[0] is SwitchInstruction switchInst))
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return false;
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newSwitch = BuildLiftedSwitch(nullCaseBlock, switchInst, new LdLoc(switchValueVar));
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return true;
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}
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static SwitchInstruction BuildLiftedSwitch(Block nullCaseBlock, SwitchInstruction switchInst, ILInstruction switchValue)
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{
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SwitchInstruction newSwitch = new SwitchInstruction(switchValue);
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newSwitch.IsLifted = true;
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newSwitch.Sections.AddRange(switchInst.Sections);
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newSwitch.Sections.Add(new SwitchSection { Body = new Branch(nullCaseBlock), HasNullLabel = true });
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return newSwitch;
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}
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/// <summary>
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/// Matches Roslyn C# switch on nullable.
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/// </summary>
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bool MatchRoslynSwitchOnNullable(InstructionCollection<ILInstruction> instructions, int i, out SwitchInstruction newSwitch)
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{
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newSwitch = null;
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// match first block:
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// if (logic.not(call get_HasValue(target))) br nullCaseBlock
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// br switchBlock
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if (!instructions[i].MatchIfInstruction(out var condition, out var trueInst))
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return false;
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if (!instructions[i + 1].MatchBranch(out var switchBlock) || !trueInst.MatchBranch(out var nullCaseBlock))
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return false;
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if (!condition.MatchLogicNot(out var getHasValue) || !NullableLiftingTransform.MatchHasValueCall(getHasValue, out ILInstruction target) || !SemanticHelper.IsPure(target.Flags))
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return false;
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// match second block: switchBlock
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// note: I have seen cases where switchVar is inlined into the switch.
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// stloc switchVar(call GetValueOrDefault(ldloca tmp))
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// switch (ldloc switchVar) {
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// case [0..1): br caseBlock1
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// ... more cases ...
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// case [long.MinValue..0),[1..5),[6..10),[11..long.MaxValue]: br defaultBlock
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// }
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if (switchBlock.IncomingEdgeCount != 1)
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return false;
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SwitchInstruction switchInst;
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switch (switchBlock.Instructions.Count)
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{
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case 2:
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{
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// this is the normal case described by the pattern above
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if (!switchBlock.Instructions[0].MatchStLoc(out var switchVar, out var getValueOrDefault))
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return false;
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if (!switchVar.IsSingleDefinition || switchVar.LoadCount != 1)
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return false;
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if (!(NullableLiftingTransform.MatchGetValueOrDefault(getValueOrDefault, out ILInstruction target2) && target2.Match(target).Success))
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return false;
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if (!(switchBlock.Instructions[1] is SwitchInstruction si))
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return false;
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switchInst = si;
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break;
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}
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case 1:
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{
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// this is the special case where `call GetValueOrDefault(ldloca tmp)` is inlined into the switch.
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if (!(switchBlock.Instructions[0] is SwitchInstruction si))
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return false;
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if (!(NullableLiftingTransform.MatchGetValueOrDefault(si.Value, out ILInstruction target2) && target2.Match(target).Success))
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return false;
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switchInst = si;
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break;
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}
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default:
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{
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return false;
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}
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}
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ILInstruction switchValue;
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if (target.MatchLdLoca(out var v))
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switchValue = new LdLoc(v).WithILRange(target);
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else
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switchValue = new LdObj(target, ((CallInstruction)getHasValue).Method.DeclaringType);
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newSwitch = BuildLiftedSwitch(nullCaseBlock, switchInst, switchValue);
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return true;
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}
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}
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}
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