// Copyright (c) 2017 Siegfried Pammer
//
// 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.
using System;
using System.Collections.Generic;
using System.Linq;
using ICSharpCode.Decompiler.IL.ControlFlow;
using ICSharpCode.Decompiler.TypeSystem;
using ICSharpCode.Decompiler.Util;
namespace ICSharpCode.Decompiler.IL.Transforms
{
using HashtableInitializer = Dictionary<IField, (List<(string, int)> Labels, IfInstruction JumpToNext, Block ContainingBlock, Block Previous, Block Next, bool Transformed)>;
/// <summary>
/// Detects switch-on-string patterns employed by the C# compiler and transforms them to an ILAst-switch-instruction.
/// </summary>
public class SwitchOnStringTransform : IILTransform
{
ILTransformContext context;
public void Run(ILFunction function, ILTransformContext context)
{
if (!context.Settings.SwitchStatementOnString)
return;
this.context = context;
BlockContainer body = (BlockContainer)function.Body;
var hashtableInitializers = ScanHashtableInitializerBlocks(body.EntryPoint);
HashSet<BlockContainer> changedContainers = new HashSet<BlockContainer>();
foreach (var block in function.Descendants.OfType<Block>())
{
bool changed = false;
if (block.IncomingEdgeCount == 0)
continue;
for (int i = block.Instructions.Count - 1; i >= 0; i--)
{
if (SimplifyCascadingIfStatements(block.Instructions, ref i))
{
changed = true;
continue;
}
if (SimplifyCSharp1CascadingIfStatements(block.Instructions, ref i))
{
changed = true;
continue;
}
if (MatchLegacySwitchOnStringWithHashtable(block, hashtableInitializers, ref i))
{
changed = true;
continue;
}
if (MatchLegacySwitchOnStringWithDict(block.Instructions, ref i))
{
changed = true;
continue;
}
if (MatchRoslynSwitchOnString(block.Instructions, ref i))
{
changed = true;
continue;
}
}
if (!changed)
continue;
SwitchDetection.SimplifySwitchInstruction(block, context);
if (block.Parent is BlockContainer container)
changedContainers.Add(container);
}
var omittedBlocks = new Dictionary<Block, Block>();
// Remove all transformed hashtable initializers from the entrypoint.
foreach (var item in hashtableInitializers)
{
var (labels, jumpToNext, containingBlock, previous, next, transformed) = item.Value;
if (!transformed)
continue;
if (!omittedBlocks.TryGetValue(previous, out var actual))
actual = previous;
context.Step("Remove hashtable initializer", actual);
if (jumpToNext != null)
{
actual.Instructions.SecondToLastOrDefault().ReplaceWith(jumpToNext);
}
actual.Instructions.LastOrDefault().ReplaceWith(new Branch(next));
omittedBlocks.Add(containingBlock, previous);
changedContainers.Add(body);
}
// If all initializer where removed, remove the initial null check as well.
if (hashtableInitializers.Count > 0 && omittedBlocks.Count == hashtableInitializers.Count && body.EntryPoint.Instructions.Count == 2)
{
if (body.EntryPoint.Instructions[0] is IfInstruction ifInst
&& ifInst.TrueInst.MatchBranch(out var beginOfMethod) && body.EntryPoint.Instructions[1].MatchBranch(beginOfMethod))
{
context.Step("Remove initial null check", body);
body.EntryPoint.Instructions.RemoveAt(0);
}
}
foreach (var container in changedContainers)
container.SortBlocks(deleteUnreachableBlocks: true);
}
HashtableInitializer ScanHashtableInitializerBlocks(Block entryPoint)
{
var hashtables = new HashtableInitializer();
if (entryPoint.Instructions.Count != 2)
return hashtables;
// match first block: checking compiler-generated Hashtable for null
// if (comp(volatile.ldobj System.Collections.Hashtable(ldsflda $$method0x600003f-1) != ldnull)) br switchHeadBlock
// br tableInitBlock
if (!(entryPoint.Instructions[0].MatchIfInstruction(out var condition, out var branchToSwitchHead)))
return hashtables;
if (!entryPoint.Instructions[1].MatchBranch(out var tableInitBlock))
return hashtables;
if (!(condition.MatchCompNotEquals(out var left, out var right) && right.MatchLdNull() &&
MatchDictionaryFieldLoad(left, IsNonGenericHashtable, out var dictField, out var dictionaryType)))
return hashtables;
if (!branchToSwitchHead.MatchBranch(out var switchHead))
return hashtables;
// match second block: initialization of compiler-generated Hashtable
// stloc table(newobj Hashtable..ctor(ldc.i4 capacity, ldc.f loadFactor))
// call Add(ldloc table, ldstr value, box System.Int32(ldc.i4 index))
// ... more calls to Add ...
// volatile.stobj System.Collections.Hashtable(ldsflda $$method0x600003f - 1, ldloc table)
// br switchHeadBlock
if (tableInitBlock.IncomingEdgeCount != 1 || tableInitBlock.Instructions.Count < 3)
return hashtables;
Block previousBlock = entryPoint;
while (tableInitBlock != null)
{
if (!ExtractStringValuesFromInitBlock(tableInitBlock, out var stringValues, out var blockAfterThisInitBlock, dictionaryType, dictField, true))
break;
var nextHashtableInitHead = tableInitBlock.Instructions.SecondToLastOrDefault() as IfInstruction;
hashtables.Add(dictField, (stringValues, nextHashtableInitHead, tableInitBlock, previousBlock, blockAfterThisInitBlock, false));
previousBlock = tableInitBlock;
// if there is another IfInstruction before the end of the block, it might be a jump to the next hashtable init block.
// if (comp(volatile.ldobj System.Collections.Hashtable(ldsflda $$method0x600003f-2) != ldnull)) br switchHeadBlock
if (nextHashtableInitHead != null)
{
if (!(nextHashtableInitHead.Condition.MatchCompNotEquals(out left, out right) && right.MatchLdNull() &&
MatchDictionaryFieldLoad(left, IsNonGenericHashtable, out var nextDictField, out _)))
break;
if (!nextHashtableInitHead.TrueInst.MatchBranch(switchHead))
break;
tableInitBlock = blockAfterThisInitBlock;
dictField = nextDictField;
}
else
{
break;
}
}
return hashtables;
}
bool SimplifyCascadingIfStatements(InstructionCollection<ILInstruction> instructions, ref int i)
{
// match first block: checking switch-value for null or first value (Roslyn)
// if (call op_Equality(ldloc switchValueVar, ldstr value)) br firstBlock
// -or-
// if (comp(ldloc switchValueVar == ldnull)) br defaultBlock
if (!instructions[i].MatchIfInstruction(out var condition, out var firstBlockOrDefaultJump))
return false;
var nextCaseJump = instructions[i + 1];
while (condition.MatchLogicNot(out var arg))
{
condition = arg;
ExtensionMethods.Swap(ref firstBlockOrDefaultJump, ref nextCaseJump);
}
// match call to operator ==(string, string)
if (!MatchStringEqualityComparison(condition, out var switchValueVar, out string firstBlockValue, out bool isVBCompareString))
return false;
if (isVBCompareString)
{
ExtensionMethods.Swap(ref firstBlockOrDefaultJump, ref nextCaseJump);
}
if (firstBlockOrDefaultJump.MatchBranch(out var firstBlock))
{
// success
}
else if (firstBlockOrDefaultJump.MatchLeave(out _))
{
firstBlock = null;
// success
}
else
{
return false;
}
var values = new List<(string, ILInstruction)>();
var uniqueValues = new HashSet<string>();
int numberOfUniqueMatchesWithCurrentVariable = 0;
HashSet<Block> caseBlocks = new HashSet<Block>();
caseBlocks.Add((Block)instructions[i].Parent);
bool AddSwitchSection(string value, ILInstruction inst)
{
if (!uniqueValues.Add(value))
return false;
numberOfUniqueMatchesWithCurrentVariable++;
values.Add((value, inst));
return true;
}
ILInstruction switchValue = null;
if (isVBCompareString && string.IsNullOrEmpty(firstBlockValue))
{
if (!AddSwitchSection(null, firstBlock ?? firstBlockOrDefaultJump))
return false;
if (!AddSwitchSection(string.Empty, firstBlock ?? firstBlockOrDefaultJump))
return false;
}
else
{
if (!AddSwitchSection(firstBlockValue, firstBlock ?? firstBlockOrDefaultJump))
return false;
}
bool removeExtraLoad = false;
bool keepAssignmentBefore = false;
if (i >= 1 && instructions[i - 1].MatchStLoc(switchValueVar, out switchValue))
{
// stloc switchValueVar(switchValue)
// if (call op_Equality(ldloc switchValueVar, ldstr value)) br firstBlock
// Newer versions of Roslyn use extra variables:
if (i >= 2 && switchValue.MatchLdLoc(out var otherSwitchValueVar) && otherSwitchValueVar.IsSingleDefinition && otherSwitchValueVar.LoadCount == 1
&& instructions[i - 2].MatchStLoc(otherSwitchValueVar, out var newSwitchValue))
{
switchValue = newSwitchValue;
removeExtraLoad = true;
}
}
else if (i >= 1 && instructions[i - 1] is StLoc stloc)
{
if (stloc.Value.MatchLdLoc(switchValueVar))
{
// in case of optimized legacy code there are two stlocs:
// stloc otherSwitchValueVar(ldloc switchValue)
// stloc switchValueVar(ldloc otherSwitchValueVar)
// if (call op_Equality(ldloc otherSwitchValueVar, ldstr value)) br firstBlock
var otherSwitchValueVar = switchValueVar;
switchValueVar = stloc.Variable;
numberOfUniqueMatchesWithCurrentVariable = 0;
if (i >= 2 && instructions[i - 2].MatchStLoc(otherSwitchValueVar, out switchValue)
&& otherSwitchValueVar.IsSingleDefinition && otherSwitchValueVar.LoadCount == 2)
{
removeExtraLoad = true;
}
else
{
switchValue = new LdLoc(otherSwitchValueVar);
}
}
else
{
// Variable before the start of the switch is not related to the switch.
keepAssignmentBefore = true;
switchValue = new LdLoc(switchValueVar);
}
}
else
{
// Instruction before the start of the switch is not related to the switch.
keepAssignmentBefore = true;
switchValue = new LdLoc(switchValueVar);
}
// if instruction must be followed by a branch to the next case
if (!nextCaseJump.MatchBranch(out Block currentCaseBlock))
return false;
// extract all cases and add them to the values list.
ILInstruction nextCaseBlock;
do
{
nextCaseBlock = MatchCaseBlock(currentCaseBlock, switchValueVar, out string value, out bool emptyStringEqualsNull, out ILInstruction block);
if (nextCaseBlock == null)
break;
if (emptyStringEqualsNull && string.IsNullOrEmpty(value))
{
if (!AddSwitchSection(null, block))
return false;
if (!AddSwitchSection(string.Empty, block))
return false;
}
else
{
if (!AddSwitchSection(value, block))
return false;
}
caseBlocks.Add(currentCaseBlock);
currentCaseBlock = nextCaseBlock as Block;
} while (currentCaseBlock != null);
// We didn't find enough cases, exit
if (values.Count < 3)
return false;
context.Step(nameof(SimplifyCascadingIfStatements), instructions[i]);
// if the switchValueVar is used in other places as well, do not eliminate the store.
if (switchValueVar.LoadCount > numberOfUniqueMatchesWithCurrentVariable || !ValidateUsesOfSwitchValueVariable(switchValueVar, caseBlocks))
{
keepAssignmentBefore = true;
removeExtraLoad = false; // prevent loads from being deleted after detecting that
// we have to keep the assignment before the switch statement
switchValue = new LdLoc(switchValueVar);
}
int offset = firstBlock == null ? 1 : 0;
var sections = new List<SwitchSection>(values.Skip(offset).SelectWithIndex((index, s) => new SwitchSection { Labels = new LongSet(index), Body = s.Item2 is Block b ? new Branch(b) : s.Item2.Clone() }));
sections.Add(new SwitchSection { Labels = new LongSet(new LongInterval(0, sections.Count)).Invert(), Body = currentCaseBlock != null ? (ILInstruction)new Branch(currentCaseBlock) : new Leave((BlockContainer)nextCaseBlock) });
var stringToInt = new StringToInt(switchValue, values.Skip(offset).Select(item => item.Item1).ToArray());
var inst = new SwitchInstruction(stringToInt);
inst.Sections.AddRange(sections);
if (removeExtraLoad)
{
inst.AddILRange(instructions[i - 2]);
instructions[i - 2].ReplaceWith(inst);
instructions.RemoveRange(i - 1, 3);
i -= 2;
}
else
{
if (keepAssignmentBefore)
{
inst.AddILRange(instructions[i]);
instructions[i].ReplaceWith(inst);
instructions.RemoveAt(i + 1);
}
else
{
inst.AddILRange(instructions[i - 1]);
instructions[i - 1].ReplaceWith(inst);
instructions.RemoveRange(i, 2);
i--;
}
}
return true;
}
private bool ValidateUsesOfSwitchValueVariable(ILVariable switchValueVar, HashSet<Block> caseBlocks)
{
foreach (var use in switchValueVar.LoadInstructions)
{
bool isValid = false;
foreach (var caseBlock in caseBlocks)
{
if (use.IsDescendantOf(caseBlock))
isValid = true;
}
if (!isValid)
return false;
}
return true;
}
bool SimplifyCSharp1CascadingIfStatements(InstructionCollection<ILInstruction> instructions, ref int i)
{
if (i < 1)
return false;
// match first block:
// stloc switchValueVar(ldloc temp)
// if (comp(ldloc temp == ldnull)) br defaultBlock
// br isInternedBlock
if (!(instructions[i].MatchIfInstruction(out var condition, out var defaultBlockJump)))
return false;
if (!instructions[i + 1].MatchBranch(out var isInternedBlock))
return false;
if (!defaultBlockJump.MatchBranch(out var defaultOrNullBlock))
return false;
if (!(condition.MatchCompEqualsNull(out var tempLoad) && tempLoad.MatchLdLoc(out var temp)))
return false;
if (!(temp.Kind == VariableKind.StackSlot && temp.LoadCount == 2))
return false;
if (!(instructions[i - 1].MatchStLoc(out var switchValueVar, out var switchValue) && switchValue.MatchLdLoc(temp)))
return false;
// match isInternedBlock:
// stloc switchValueVarCopy(call IsInterned(ldloc switchValueVar))
// if (comp(ldloc switchValueVarCopy == ldstr "case1")) br caseBlock1
// br caseHeader2
if (isInternedBlock.IncomingEdgeCount != 1 || isInternedBlock.Instructions.Count != 3)
return false;
if (!(isInternedBlock.Instructions[0].MatchStLoc(out var switchValueVarCopy, out var arg) && IsIsInternedCall(arg as Call, out arg) && arg.MatchLdLoc(switchValueVar)))
return false;
switchValueVar = switchValueVarCopy;
int conditionOffset = 1;
Block currentCaseBlock = isInternedBlock;
var values = new List<(string, ILInstruction)>();
if (!switchValueVarCopy.IsSingleDefinition)
return false;
// each case starts with:
// if (comp(ldloc switchValueVar == ldstr "case label")) br caseBlock
// br currentCaseBlock
while (currentCaseBlock.Instructions[conditionOffset].MatchIfInstruction(out condition, out var caseBlockJump))
{
if (currentCaseBlock.Instructions.Count != conditionOffset + 2)
break;
if (!condition.MatchCompEquals(out var left, out var right))
break;
if (!left.MatchLdLoc(switchValueVar))
break;
if (!right.MatchLdStr(out string value))
break;
if (!(caseBlockJump.MatchBranch(out var caseBlock) || caseBlockJump.MatchLeave((BlockContainer)currentCaseBlock.Parent)))
break;
if (!currentCaseBlock.Instructions[conditionOffset + 1].MatchBranch(out currentCaseBlock))
break;
conditionOffset = 0;
values.Add((value, caseBlockJump.Clone()));
}
if (values.Count != switchValueVarCopy.LoadCount)
return false;
context.Step(nameof(SimplifyCSharp1CascadingIfStatements), instructions[i]);
// switch contains case null:
if (currentCaseBlock != defaultOrNullBlock)
{
values.Add((null, new Branch(defaultOrNullBlock)));
}
var sections = new List<SwitchSection>(values.SelectWithIndex((index, b) => new SwitchSection { Labels = new LongSet(index), Body = b.Item2 }));
sections.Add(new SwitchSection { Labels = new LongSet(new LongInterval(0, sections.Count)).Invert(), Body = new Branch(currentCaseBlock) });
var stringToInt = new StringToInt(switchValue, values.SelectArray(item => item.Item1));
var inst = new SwitchInstruction(stringToInt);
inst.Sections.AddRange(sections);
inst.AddILRange(instructions[i - 1]);
instructions[i].ReplaceWith(inst);
instructions.RemoveAt(i + 1);
instructions.RemoveAt(i - 1);
return true;
}
bool IsIsInternedCall(Call call, out ILInstruction argument)
{
if (call != null
&& call.Method.DeclaringType.IsKnownType(KnownTypeCode.String)
&& call.Method.IsStatic
&& call.Method.Name == "IsInterned"
&& call.Arguments.Count == 1)
{
argument = call.Arguments[0];
return true;
}
argument = null;
return false;
}
/// <summary>
/// Each case consists of two blocks:
/// 1. block:
/// if (call op_Equality(ldloc switchVariable, ldstr value)) br caseBlock
/// br nextBlock
/// -or-
/// if (comp(ldloc switchValueVar == ldnull)) br nextBlock
/// br caseBlock
/// 2. block is caseBlock
/// This method matches the above pattern or its inverted form:
/// the call to ==(string, string) is wrapped in logic.not and the branch targets are reversed.
/// Returns the next block that follows in the block-chain.
/// The <paramref name="switchVariable"/> is updated if the value gets copied to a different variable.
/// See comments below for more info.
/// </summary>
ILInstruction MatchCaseBlock(Block currentBlock, ILVariable switchVariable, out string value, out bool emptyStringEqualsNull, out ILInstruction caseBlockOrLeave)
{
value = null;
caseBlockOrLeave = null;
emptyStringEqualsNull = false;
if (currentBlock.IncomingEdgeCount != 1 || currentBlock.Instructions.Count != 2)
return null;
if (!currentBlock.MatchIfAtEndOfBlock(out var condition, out var caseBlockBranch, out var nextBlockBranch))
return null;
if (!MatchStringEqualityComparison(condition, switchVariable, out value, out bool isVBCompareString))
{
return null;
}
if (isVBCompareString)
{
ExtensionMethods.Swap(ref caseBlockBranch, ref nextBlockBranch);
emptyStringEqualsNull = true;
}
if (caseBlockBranch.MatchBranch(out var caseBlock))
{
caseBlockOrLeave = caseBlock;
}
else if (caseBlockBranch.MatchLeave(out _))
{
caseBlockOrLeave = caseBlockBranch;
}
else
{
return null;
}
if (nextBlockBranch.MatchBranch(out Block nextBlock))
{
// success
return nextBlock;
}
else if (nextBlockBranch.MatchLeave(out BlockContainer blockContainer))
{
// success
return blockContainer;
}
else
{
return null;
}
}
/// <summary>
/// Matches the C# 2.0 switch-on-string pattern, which uses Dictionary<string, int>.
/// </summary>
bool MatchLegacySwitchOnStringWithDict(InstructionCollection<ILInstruction> instructions, ref int i)
{
// match first block: checking switch-value for null:
// (In some cases, i.e., if switchValueVar is a parameter, the initial store is optional.)
// stloc switchValueVar(switchValue)
// if (comp(ldloc switchValueVar == ldnull)) br nullCase
// br nextBlock
if (!instructions[i].MatchIfInstruction(out var condition, out var exitBlockJump))
return false;
if (!(condition.MatchCompEquals(out var left, out var right) && right.MatchLdNull()))
return false;
// The initial store can be omitted in some cases. If there is no initial store or the switch value variable is reused later,
// we do not inline the "switch value", but create an extra load later on.
if (i > 0 && instructions[i - 1].MatchStLoc(out var switchValueVar, out var switchValue))
{
if (!(switchValueVar.IsSingleDefinition && ((SemanticHelper.IsPure(switchValue.Flags) && left.Match(switchValue).Success) || left.MatchLdLoc(switchValueVar))))
return false;
}
else
{
if (!left.MatchLdLoc(out switchValueVar))
return false;
switchValue = null;
}
if (!switchValueVar.Type.IsKnownType(KnownTypeCode.String))
return false;
// either br nullCase or leave container
BlockContainer leaveContainer = null;
if (!exitBlockJump.MatchBranch(out var nullValueCaseBlock) && !exitBlockJump.MatchLeave(out leaveContainer))
return false;
var nextBlockJump = instructions.ElementAtOrDefault(i + 1) as Branch;
if (nextBlockJump == null || nextBlockJump.TargetBlock.IncomingEdgeCount != 1)
return false;
// match second block: checking compiler-generated Dictionary<string, int> for null
// if (comp(volatile.ldobj System.Collections.Generic.Dictionary`2[[System.String],[System.Int32]](ldsflda $$method0x600000c-1) != ldnull)) br caseNullBlock
// br dictInitBlock
var nextBlock = nextBlockJump.TargetBlock;
if (nextBlock.Instructions.Count != 2 || !nextBlock.Instructions[0].MatchIfInstruction(out condition, out var tryGetValueBlockJump))
return false;
if (!tryGetValueBlockJump.MatchBranch(out var tryGetValueBlock))
return false;
if (!nextBlock.Instructions[1].MatchBranch(out var dictInitBlock) || dictInitBlock.IncomingEdgeCount != 1)
return false;
if (!(condition.MatchCompNotEquals(out left, out right) && right.MatchLdNull() &&
MatchDictionaryFieldLoad(left, IsStringToIntDictionary, out var dictField, out var dictionaryType)))
return false;
// match third block: initialization of compiler-generated Dictionary<string, int>
// stloc dict(newobj Dictionary..ctor(ldc.i4 valuesLength))
// call Add(ldloc dict, ldstr value, ldc.i4 index)
// ... more calls to Add ...
// volatile.stobj System.Collections.Generic.Dictionary`2[[System.String],[System.Int32]](ldsflda $$method0x600003f-1, ldloc dict)
// br switchHeadBlock
if (dictInitBlock.IncomingEdgeCount != 1 || dictInitBlock.Instructions.Count < 3)
return false;
if (!ExtractStringValuesFromInitBlock(dictInitBlock, out var stringValues, out var blockAfterInit, dictionaryType, dictField, false))
return false;
if (tryGetValueBlock != blockAfterInit)
return false;
// match fourth block: TryGetValue on compiler-generated Dictionary<string, int>
// if (logic.not(call TryGetValue(volatile.ldobj System.Collections.Generic.Dictionary`2[[System.String],[System.Int32]](ldsflda $$method0x600000c-1), ldloc switchValueVar, ldloca switchIndexVar))) br defaultBlock
// br switchBlock
if (tryGetValueBlock.IncomingEdgeCount != 2 || tryGetValueBlock.Instructions.Count != 2)
return false;
if (!tryGetValueBlock.Instructions[0].MatchIfInstruction(out condition, out var defaultBlockJump))
return false;
if (!defaultBlockJump.MatchBranch(out var defaultBlock) && !((leaveContainer != null && defaultBlockJump.MatchLeave(leaveContainer)) || defaultBlockJump.MatchLeave(out _)))
return false;
if (!(condition.MatchLogicNot(out var arg) && arg is CallInstruction c && c.Method.Name == "TryGetValue" &&
MatchDictionaryFieldLoad(c.Arguments[0], IsStringToIntDictionary, out var dictField2, out _) && dictField2.Equals(dictField)))
return false;
if (!c.Arguments[1].MatchLdLoc(switchValueVar) || !c.Arguments[2].MatchLdLoca(out var switchIndexVar))
return false;
if (!tryGetValueBlock.Instructions[1].MatchBranch(out var switchBlock))
return false;
// match fifth block: switch-instruction block
// switch (ldloc switchVariable) {
// case [0..1): br caseBlock1
// ... more cases ...
// case [long.MinValue..0),[13..long.MaxValue]: br defaultBlock
// }
// mcs has a bug: when there is only one case it still generates the full-blown Dictionary<string, int> pattern,
// but uses only a simple if statement instead of the switch instruction.
if (switchBlock.IncomingEdgeCount != 1 || switchBlock.Instructions.Count == 0)
return false;
var sections = new List<SwitchSection>();
switch (switchBlock.Instructions[0])
{
case SwitchInstruction switchInst:
if (switchBlock.Instructions.Count != 1)
return false;
if (!switchInst.Value.MatchLdLoc(switchIndexVar))
return false;
sections.AddRange(switchInst.Sections);
break;
case IfInstruction ifInst:
if (switchBlock.Instructions.Count != 2)
return false;
if (!ifInst.Condition.MatchCompEquals(out left, out right))
return false;
if (!left.MatchLdLoc(switchIndexVar))
return false;
if (!right.MatchLdcI4(0))
return false;
sections.Add(new SwitchSection() { Body = ifInst.TrueInst, Labels = new LongSet(0) }.WithILRange(ifInst));
sections.Add(new SwitchSection() { Body = switchBlock.Instructions[1], Labels = new LongSet(0).Invert() }.WithILRange(switchBlock.Instructions[1]));
break;
}
// mcs: map sections without a value to the default section, if possible
if (!FixCasesWithoutValue(sections, stringValues))
return false;
// switch contains case null:
if (nullValueCaseBlock != defaultBlock)
{
if (!AddNullSection(sections, stringValues, nullValueCaseBlock))
{
return false;
}
}
context.Step(nameof(MatchLegacySwitchOnStringWithDict), instructions[i]);
bool keepAssignmentBefore = false;
if (switchValueVar.LoadCount > 2 || switchValue == null)
{
switchValue = new LdLoc(switchValueVar);
keepAssignmentBefore = true;
}
var stringToInt = new StringToInt(switchValue, stringValues);
var inst = new SwitchInstruction(stringToInt);
inst.Sections.AddRange(sections);
instructions[i + 1].ReplaceWith(inst);
if (keepAssignmentBefore)
{
// delete if (comp(ldloc switchValueVar == ldnull))
inst.AddILRange(instructions[i]);
instructions.RemoveAt(i);
i--;
}
else
{
// delete both the if and the assignment before
inst.AddILRange(instructions[i - 1]);
instructions.RemoveRange(i - 1, 2);
i -= 2;
}
return true;
}
bool FixCasesWithoutValue(List<SwitchSection> sections, List<(string, int)> stringValues)
{
bool HasLabel(SwitchSection section)
{
return section.Labels.Values.Any(i => stringValues.Any(value => i == value.Item2));
}
// Pick the section with the most labels as default section.
// And collect all sections that have no value mapped to them.
SwitchSection defaultSection = sections.First();
List<SwitchSection> sectionsWithoutLabels = new List<SwitchSection>();
foreach (var section in sections)
{
if (section == defaultSection)
continue;
if (section.Labels.Count() > defaultSection.Labels.Count())
{
if (!HasLabel(defaultSection))
sectionsWithoutLabels.Add(defaultSection);
defaultSection = section;
continue;
}
if (!HasLabel(section))
sectionsWithoutLabels.Add(section);
}
foreach (var section in sectionsWithoutLabels)
{
if (!section.Body.Match(defaultSection.Body).Success)
return false;
defaultSection.Labels = defaultSection.Labels.UnionWith(section.Labels);
if (section.HasNullLabel)
defaultSection.HasNullLabel = true;
sections.Remove(section);
}
return true;
}
bool AddNullSection(List<SwitchSection> sections, List<(string Value, int Index)> stringValues, Block nullValueCaseBlock)
{
var label = new LongSet(stringValues.Max(item => item.Index) + 1);
var possibleConflicts = sections.Where(sec => sec.Labels.Overlaps(label)).ToArray();
if (possibleConflicts.Length > 1)
return false;
else if (possibleConflicts.Length == 1)
{
if (possibleConflicts[0].Labels.Count() == 1)
return false; // cannot remove only label
possibleConflicts[0].Labels = possibleConflicts[0].Labels.ExceptWith(label);
}
stringValues.Add((null, (int)label.Values.First()));
sections.Add(new SwitchSection() { Labels = label, Body = new Branch(nullValueCaseBlock) });
return true;
}
/// <summary>
/// Matches 'volatile.ldobj dictionaryType(ldsflda dictField)'
/// </summary>
bool MatchDictionaryFieldLoad(ILInstruction inst, Func<IType, bool> typeMatcher, out IField dictField, out IType dictionaryType)
{
dictField = null;
dictionaryType = null;
return inst.MatchLdObj(out var dictionaryFieldLoad, out dictionaryType) &&
typeMatcher(dictionaryType) &&
dictionaryFieldLoad.MatchLdsFlda(out dictField) &&
(dictField.IsCompilerGeneratedOrIsInCompilerGeneratedClass() || dictField.Name.StartsWith("$$method", StringComparison.Ordinal));
}
/// <summary>
/// Matches and extracts values from Add-call sequences.
/// </summary>
bool ExtractStringValuesFromInitBlock(Block block, out List<(string, int)> values, out Block blockAfterInit, IType dictionaryType, IField dictionaryField, bool isHashtablePattern)
{
values = null;
blockAfterInit = null;
// stloc dictVar(newobj Dictionary..ctor(ldc.i4 valuesLength))
// -or-
// stloc dictVar(newobj Hashtable..ctor(ldc.i4 capacity, ldc.f4 loadFactor))
if (!(block.Instructions[0].MatchStLoc(out var dictVar, out var newObjDict) && newObjDict is NewObj newObj))
return false;
if (!newObj.Method.DeclaringType.Equals(dictionaryType))
return false;
int valuesLength = 0;
if (newObj.Arguments.Count == 2)
{
if (!newObj.Arguments[0].MatchLdcI4(out valuesLength))
return false;
if (!newObj.Arguments[1].MatchLdcF4(0.5f))
return false;
}
else if (newObj.Arguments.Count == 1)
{
if (!newObj.Arguments[0].MatchLdcI4(out valuesLength))
return false;
}
values = new List<(string, int)>(valuesLength);
int i = 0;
while (MatchAddCall(dictionaryType, block.Instructions[i + 1], dictVar, out var index, out var value))
{
values.Add((value, index));
i++;
}
// final store to compiler-generated variable:
// volatile.stobj dictionaryType(ldsflda dictionaryField, ldloc dictVar)
if (!(block.Instructions[i + 1].MatchStObj(out var loadField, out var dictVarLoad, out var dictType) &&
dictType.Equals(dictionaryType) && loadField.MatchLdsFlda(out var dictField) && dictField.Equals(dictionaryField) &&
dictVarLoad.MatchLdLoc(dictVar)))
return false;
if (isHashtablePattern && block.Instructions[i + 2] is IfInstruction)
{
return block.Instructions[i + 3].MatchBranch(out blockAfterInit);
}
return block.Instructions[i + 2].MatchBranch(out blockAfterInit);
}
/// <summary>
/// call Add(ldloc dictVar, ldstr value, ldc.i4 index)
/// -or-
/// call Add(ldloc dictVar, ldstr value, box System.Int32(ldc.i4 index))
/// </summary>
bool MatchAddCall(IType dictionaryType, ILInstruction inst, ILVariable dictVar, out int index, out string value)
{
value = null;
index = -1;
if (!(inst is CallInstruction c && c.Method.Name == "Add" && c.Arguments.Count == 3))
return false;
if (!c.Arguments[0].MatchLdLoc(dictVar))
return false;
if (!c.Arguments[1].MatchLdStr(out value))
{
if (c.Arguments[1].MatchLdsFld(out var field) && field.DeclaringType.IsKnownType(KnownTypeCode.String) && field.Name == "Empty")
{
value = "";
}
else
{
return false;
}
}
if (!(c.Method.DeclaringType.Equals(dictionaryType) && !c.Method.IsStatic))
return false;
return (c.Arguments[2].MatchLdcI4(out index) || (c.Arguments[2].MatchBox(out var arg, out _) && arg.MatchLdcI4(out index)));
}
bool IsStringToIntDictionary(IType dictionaryType)
{
if (dictionaryType.FullName != "System.Collections.Generic.Dictionary")
return false;
if (dictionaryType.TypeArguments.Count != 2)
return false;
return dictionaryType.TypeArguments[0].IsKnownType(KnownTypeCode.String) &&
dictionaryType.TypeArguments[1].IsKnownType(KnownTypeCode.Int32);
}
bool IsNonGenericHashtable(IType dictionaryType)
{
if (dictionaryType.FullName != "System.Collections.Hashtable")
return false;
if (dictionaryType.TypeArguments.Count != 0)
return false;
return true;
}
bool MatchLegacySwitchOnStringWithHashtable(Block block, HashtableInitializer hashtableInitializers, ref int i)
{
// match first block: checking switch-value for null
// stloc tmp(ldloc switch-value)
// stloc switchVariable(ldloc tmp)
// if (comp(ldloc tmp == ldnull)) br nullCaseBlock
// br getItemBloc
if (block.Instructions.Count != i + 4)
return false;
if (!block.Instructions[i].MatchStLoc(out var tmp, out var switchValue))
return false;
if (!block.Instructions[i + 1].MatchStLoc(out var switchVariable, out var tmpLoad) || !tmpLoad.MatchLdLoc(tmp))
return false;
if (!block.Instructions[i + 2].MatchIfInstruction(out var condition, out var nullCaseBlockBranch))
return false;
if (!block.Instructions[i + 3].MatchBranch(out var getItemBlock) || !(nullCaseBlockBranch.MatchBranch(out var nullCaseBlock) || nullCaseBlockBranch is Leave))
return false;
if (!(condition.MatchCompEquals(out var left, out var right) && right.MatchLdNull() && left.MatchLdLoc(tmp)))
return false;
// match second block: get_Item on compiler-generated Hashtable
// stloc tmp2(call get_Item(volatile.ldobj System.Collections.Hashtable(ldsflda $$method0x600003f - 1), ldloc switchVariable))
// stloc switchVariable(ldloc tmp2)
// if (comp(ldloc tmp2 == ldnull)) br defaultCaseBlock
// br switchBlock
if (getItemBlock.IncomingEdgeCount != 1 || getItemBlock.Instructions.Count != 4)
return false;
if (!(getItemBlock.Instructions[0].MatchStLoc(out var tmp2, out var getItem) && getItem is Call getItemCall && getItemCall.Method.Name == "get_Item"))
return false;
if (!getItemBlock.Instructions[1].MatchStLoc(out var switchVariable2, out var tmp2Load) || !tmp2Load.MatchLdLoc(tmp2))
return false;
if (!ILVariableEqualityComparer.Instance.Equals(switchVariable, switchVariable2))
return false;
if (!getItemBlock.Instructions[2].MatchIfInstruction(out condition, out var defaultBlockBranch))
return false;
if (!getItemBlock.Instructions[3].MatchBranch(out var switchBlock) || !(defaultBlockBranch.MatchBranch(out var defaultBlock) || defaultBlockBranch is Leave))
return false;
if (!(condition.MatchCompEquals(out left, out right) && right.MatchLdNull() && left.MatchLdLoc(tmp2)))
return false;
if (!(getItemCall.Arguments.Count == 2 && MatchDictionaryFieldLoad(getItemCall.Arguments[0], IsNonGenericHashtable, out var dictField, out _) && getItemCall.Arguments[1].MatchLdLoc(switchVariable)))
return false;
// Check if there is a hashtable init block at the beginning of the method
if (!hashtableInitializers.TryGetValue(dictField, out var info))
return false;
var stringValues = info.Labels;
// match third block: switch-instruction block
// switch (ldobj System.Int32(unbox System.Int32(ldloc switchVariable))) {
// case [0..1): br caseBlock1
// ... more cases ...
// case [long.MinValue..0),[13..long.MaxValue]: br defaultBlock
// }
if (switchBlock.IncomingEdgeCount != 1 || switchBlock.Instructions.Count != 1)
return false;
if (!(switchBlock.Instructions[0] is SwitchInstruction switchInst && switchInst.Value.MatchLdObj(out var target, out var ldobjType) &&
target.MatchUnbox(out var arg, out var unboxType) && arg.MatchLdLoc(switchVariable2) && ldobjType.IsKnownType(KnownTypeCode.Int32) && unboxType.Equals(ldobjType)))
return false;
var sections = new List<SwitchSection>(switchInst.Sections);
// switch contains case null:
if (!(nullCaseBlockBranch is Leave) && nullCaseBlock != defaultBlock)
{
if (!AddNullSection(sections, stringValues, nullCaseBlock))
{
return false;
}
}
context.Step(nameof(MatchLegacySwitchOnStringWithHashtable), block.Instructions[i]);
var stringToInt = new StringToInt(switchValue, stringValues);
var inst = new SwitchInstruction(stringToInt);
inst.Sections.AddRange(sections);
inst.AddILRange(block.Instructions[i]);
block.Instructions[i].ReplaceWith(inst);
block.Instructions.RemoveRange(i + 1, 3);
info.Transformed = true;
hashtableInitializers[dictField] = info;
return true;
}
bool FindHashtableInitBlock(Block entryPoint, out List<(string, int)> stringValues, out IField dictField, out Block blockAfterThisInitBlock, out ILInstruction thisSwitchInitJumpInst, out ILInstruction nextSwitchInitJumpInst)
{
stringValues = null;
dictField = null;
blockAfterThisInitBlock = null;
nextSwitchInitJumpInst = null;
thisSwitchInitJumpInst = null;
if (entryPoint.Instructions.Count != 2)
return false;
// match first block: checking compiler-generated Hashtable for null
// if (comp(volatile.ldobj System.Collections.Hashtable(ldsflda $$method0x600003f-1) != ldnull)) br switchHeadBlock
// br tableInitBlock
if (!(entryPoint.Instructions[0].MatchIfInstruction(out var condition, out var branchToSwitchHead)))
return false;
if (!entryPoint.Instructions[1].MatchBranch(out var tableInitBlock))
return false;
if (!(condition.MatchCompNotEquals(out var left, out var right) && right.MatchLdNull() &&
MatchDictionaryFieldLoad(left, IsNonGenericHashtable, out dictField, out var dictionaryType)))
return false;
if (!branchToSwitchHead.MatchBranch(out var switchHead))
return false;
thisSwitchInitJumpInst = entryPoint.Instructions[0];
// match second block: initialization of compiler-generated Hashtable
// stloc table(newobj Hashtable..ctor(ldc.i4 capacity, ldc.f loadFactor))
// call Add(ldloc table, ldstr value, box System.Int32(ldc.i4 index))
// ... more calls to Add ...
// volatile.stobj System.Collections.Hashtable(ldsflda $$method0x600003f - 1, ldloc table)
// br switchHeadBlock
if (tableInitBlock.IncomingEdgeCount != 1 || tableInitBlock.Instructions.Count < 3)
return false;
if (!ExtractStringValuesFromInitBlock(tableInitBlock, out stringValues, out blockAfterThisInitBlock, dictionaryType, dictField, true))
return false;
// if there is another IfInstruction before the end of the block, it might be a jump to the next hashtable init block.
// if (comp(volatile.ldobj System.Collections.Hashtable(ldsflda $$method0x600003f-2) != ldnull)) br switchHeadBlock
if (tableInitBlock.Instructions.SecondToLastOrDefault() is IfInstruction nextHashtableInitHead)
{
if (!(nextHashtableInitHead.Condition.MatchCompNotEquals(out left, out right) && right.MatchLdNull() &&
MatchDictionaryFieldLoad(left, IsNonGenericHashtable, out var nextSwitchInitField, out _)))
return false;
if (!nextHashtableInitHead.TrueInst.MatchBranch(switchHead))
return false;
nextSwitchInitJumpInst = nextHashtableInitHead;
}
return true;
}
bool MatchRoslynSwitchOnString(InstructionCollection<ILInstruction> instructions, ref int i)
{
if (i >= instructions.Count - 1)
return false;
// stloc switchValueVar(switchValue)
// if (comp(ldloc switchValueVar == ldnull)) br nullCase
// br nextBlock
InstructionCollection<ILInstruction> switchBlockInstructions = instructions;
int switchBlockInstructionsOffset = i;
Block nullValueCaseBlock = null;
ILInstruction instForNullCheck = null;
if (instructions[i].MatchIfInstruction(out var condition, out var exitBlockJump)
&& condition.MatchCompEqualsNull(out instForNullCheck))
{
var nextBlockJump = instructions[i + 1] as Branch;
if (nextBlockJump == null || nextBlockJump.TargetBlock.IncomingEdgeCount != 1)
return false;
if (!exitBlockJump.MatchBranch(out nullValueCaseBlock))
return false;
switchBlockInstructions = nextBlockJump.TargetBlock.Instructions;
switchBlockInstructionsOffset = 0;
}
// stloc switchValueVar(call ComputeStringHash(switchValue))
// switch (ldloc switchValueVar) {
// case [211455823..211455824): br caseBlock1
// ... more cases ...
// case [long.MinValue..-365098645),...,[1697255802..long.MaxValue]: br defaultBlock
// }
if (!(switchBlockInstructionsOffset + 1 < switchBlockInstructions.Count && switchBlockInstructions[switchBlockInstructionsOffset + 1] is SwitchInstruction switchInst && switchInst.Value.MatchLdLoc(out var switchValueVar) &&
MatchComputeStringHashCall(switchBlockInstructions[switchBlockInstructionsOffset], switchValueVar, out LdLoc switchValueLoad)))
return false;
if (instForNullCheck != null && !instForNullCheck.MatchLdLoc(switchValueLoad.Variable))
{
return false;
}
var stringValues = new List<(string Value, ILInstruction TargetBlockOrLeave)>();
SwitchSection defaultSection = switchInst.Sections.MaxBy(s => s.Labels.Count());
if (!(defaultSection.Body.MatchBranch(out Block exitOrDefaultBlock) || defaultSection.Body.MatchLeave(out _)))
return false;
foreach (var section in switchInst.Sections)
{
if (section == defaultSection)
continue;
// extract target block
if (!section.Body.MatchBranch(out Block target))
return false;
string stringValue;
bool emptyStringEqualsNull;
if (MatchRoslynEmptyStringCaseBlockHead(target, switchValueLoad.Variable, out ILInstruction targetOrLeave, out Block currentExitBlock))
{
stringValue = "";
emptyStringEqualsNull = false;
}
else if (!MatchRoslynCaseBlockHead(target, switchValueLoad.Variable, out targetOrLeave, out currentExitBlock, out stringValue, out emptyStringEqualsNull))
{
return false;
}
if (currentExitBlock != exitOrDefaultBlock)
return false;
if (emptyStringEqualsNull && string.IsNullOrEmpty(stringValue))
{
stringValues.Add((null, targetOrLeave));
stringValues.Add((string.Empty, targetOrLeave));
}
else
{
stringValues.Add((stringValue, targetOrLeave));
}
}
if (nullValueCaseBlock != null && exitOrDefaultBlock != nullValueCaseBlock)
{
stringValues.Add((null, nullValueCaseBlock));
}
// In newer Roslyn versions (>=3.7) the null check appears in the default case, not prior to the switch.
if (!stringValues.Any(pair => pair.Value == null) && IsNullCheckInDefaultBlock(ref exitOrDefaultBlock, switchValueLoad.Variable, out nullValueCaseBlock))
{
stringValues.Add((null, nullValueCaseBlock));
}
context.Step(nameof(MatchRoslynSwitchOnString), switchValueLoad);
if (exitOrDefaultBlock != null)
{
// change TargetBlock in case it was modified by IsNullCheckInDefaultBlock()
((Branch)defaultSection.Body).TargetBlock = exitOrDefaultBlock;
}
ILInstruction switchValueInst = switchValueLoad;
if (instructions == switchBlockInstructions)
{
// stloc switchValueLoadVariable(switchValue)
// stloc switchValueVar(call ComputeStringHash(ldloc switchValueLoadVariable))
// switch (ldloc switchValueVar) {
bool keepAssignmentBefore;
// if the switchValueLoad.Variable is only used in the compiler generated case equality checks, we can remove it.
if (i >= 1 && instructions[i - 1].MatchStLoc(switchValueLoad.Variable, out var switchValueTmp) &&
switchValueLoad.Variable.IsSingleDefinition && switchValueLoad.Variable.LoadCount == switchInst.Sections.Count)
{
switchValueInst = switchValueTmp;
keepAssignmentBefore = false;
}
else
{
keepAssignmentBefore = true;
}
// replace stloc switchValueVar(call ComputeStringHash(...)) with new switch instruction
var newSwitch = ReplaceWithSwitchInstruction(i);
// remove old switch instruction
newSwitch.AddILRange(instructions[i + 1]);
instructions.RemoveAt(i + 1);
// remove extra assignment
if (!keepAssignmentBefore)
{
newSwitch.AddILRange(instructions[i - 1]);
instructions.RemoveRange(i - 1, 1);
i -= 1;
}
}
else
{
bool keepAssignmentBefore;
// if the switchValueLoad.Variable is only used in the compiler generated case equality checks, we can remove it.
if (i >= 2 && instructions[i - 2].MatchStLoc(out var temporary, out var temporaryValue) && instructions[i - 1].MatchStLoc(switchValueLoad.Variable, out var tempLoad) && tempLoad.MatchLdLoc(temporary))
{
switchValueInst = temporaryValue;
keepAssignmentBefore = false;
}
else
{
keepAssignmentBefore = true;
}
// replace null check with new switch instruction
var newSwitch = ReplaceWithSwitchInstruction(i);
newSwitch.AddILRange(switchInst);
// remove jump instruction to switch block
newSwitch.AddILRange(instructions[i + 1]);
instructions.RemoveAt(i + 1);
// remove extra assignment
if (!keepAssignmentBefore)
{
newSwitch.AddILRange(instructions[i - 2]);
instructions.RemoveRange(i - 2, 2);
i -= 2;
}
}
return true;
SwitchInstruction ReplaceWithSwitchInstruction(int offset)
{
var defaultLabel = new LongSet(new LongInterval(0, stringValues.Count)).Invert();
var values = new string[stringValues.Count];
var sections = new SwitchSection[stringValues.Count];
foreach (var (idx, (value, bodyInstruction)) in stringValues.WithIndex())
{
values[idx] = value;
var body = bodyInstruction is Block b ? new Branch(b) : bodyInstruction;
sections[idx] = new SwitchSection { Labels = new LongSet(idx), Body = body };
}
var newSwitch = new SwitchInstruction(new StringToInt(switchValueInst, values));
newSwitch.Sections.AddRange(sections);
newSwitch.Sections.Add(new SwitchSection { Labels = defaultLabel, Body = defaultSection.Body });
instructions[offset].ReplaceWith(newSwitch);
return newSwitch;
}
}
/// <summary>
/// Matches:
/// Block oldDefaultBlock (incoming: 1) {
/// if (comp.o(ldloc switchVar == ldnull)) br nullValueCaseBlock
/// br newDefaultBlock
/// }
/// </summary>
private bool IsNullCheckInDefaultBlock(ref Block exitOrDefaultBlock, ILVariable switchVar, out Block nullValueCaseBlock)
{
nullValueCaseBlock = null;
if (exitOrDefaultBlock == null)
return false;
if (!exitOrDefaultBlock.Instructions[0].MatchIfInstruction(out var condition, out var thenBranch))
return false;
if (!(condition.MatchCompEqualsNull(out var arg) && arg.MatchLdLoc(switchVar)))
return false;
if (!thenBranch.MatchBranch(out nullValueCaseBlock))
return false;
if (nullValueCaseBlock.Parent != exitOrDefaultBlock.Parent)
return false;
if (!exitOrDefaultBlock.Instructions[1].MatchBranch(out var elseBlock))
return false;
if (elseBlock.Parent != exitOrDefaultBlock.Parent)
return false;
exitOrDefaultBlock = elseBlock;
return true;
}
/// <summary>
/// Matches (and the negated version):
/// if (call op_Equality(ldloc switchValueVar, stringValue)) br body
/// br exit
/// </summary>
bool MatchRoslynCaseBlockHead(Block target, ILVariable switchValueVar, out ILInstruction bodyOrLeave, out Block defaultOrExitBlock, out string stringValue, out bool emptyStringEqualsNull)
{
bodyOrLeave = null;
defaultOrExitBlock = null;
stringValue = null;
emptyStringEqualsNull = false;
if (target.Instructions.Count != 2)
return false;
if (!target.Instructions[0].MatchIfInstruction(out var condition, out var bodyBranch))
{
// Special case: sometimes we don't have an if, because bodyBranch==exitBranch
// and the C# compiler optimized out the if.
// Example:
// Block IL_0063 (incoming: 1) {
// call op_Equality(ldloc V_4, ldstr "rowno")
// leave IL_0000(nop)
// }
condition = target.Instructions[0];
bodyBranch = target.Instructions[1];
}
ILInstruction exitBranch = target.Instructions[1];
// Handle negated conditions first:
while (condition.MatchLogicNot(out var expr))
{
ExtensionMethods.Swap(ref exitBranch, ref bodyBranch);
condition = expr;
}
if (!MatchStringEqualityComparison(condition, switchValueVar, out stringValue, out bool isVBCompareString))
return false;
if (isVBCompareString)
{
ExtensionMethods.Swap(ref exitBranch, ref bodyBranch);
emptyStringEqualsNull = true;
}
if (!(exitBranch.MatchBranch(out defaultOrExitBlock) || exitBranch.MatchLeave(out _)))
return false;
if (bodyBranch.MatchLeave(out _))
{
bodyOrLeave = bodyBranch;
return true;
}
if (bodyBranch.MatchBranch(out var bodyBlock))
{
bodyOrLeave = bodyBlock;
return true;
}
return false;
}
/// <summary>
/// Block target(incoming: 1) {
/// if (comp.o(ldloc switchValueVar == ldnull)) br exit
/// br lengthCheckBlock
/// }
///
/// Block lengthCheckBlock(incoming: 1) {
/// if (logic.not(call get_Length(ldloc switchValueVar))) br body
/// br exit
/// }
/// </summary>
bool MatchRoslynEmptyStringCaseBlockHead(Block target, ILVariable switchValueVar, out ILInstruction bodyOrLeave, out Block defaultOrExitBlock)
{
bodyOrLeave = null;
defaultOrExitBlock = null;
if (target.Instructions.Count != 2 || target.IncomingEdgeCount != 1)
return false;
if (!target.Instructions[0].MatchIfInstruction(out var nullComparisonCondition, out var exitBranch))
return false;
if (!nullComparisonCondition.MatchCompEqualsNull(out var arg) || !arg.MatchLdLoc(switchValueVar))
return false;
if (!target.Instructions[1].MatchBranch(out Block lengthCheckBlock))
return false;
if (lengthCheckBlock.Instructions.Count != 2 || lengthCheckBlock.IncomingEdgeCount != 1)
return false;
if (!lengthCheckBlock.Instructions[0].MatchIfInstruction(out var lengthCheckCondition, out var exitBranch2))
return false;
ILInstruction bodyBranch;
if (lengthCheckCondition.MatchLogicNot(out arg))
{
bodyBranch = exitBranch2;
exitBranch2 = lengthCheckBlock.Instructions[1];
lengthCheckCondition = arg;
}
else
{
bodyBranch = lengthCheckBlock.Instructions[1];
}
if (!(exitBranch2.MatchBranch(out defaultOrExitBlock) || exitBranch2.MatchLeave(out _)))
return false;
if (!MatchStringLengthCall(lengthCheckCondition, switchValueVar))
return false;
if (!exitBranch.Match(exitBranch2).Success)
return false;
if (bodyBranch.MatchLeave(out _))
{
bodyOrLeave = bodyBranch;
return true;
}
if (bodyBranch.MatchBranch(out var bodyBlock))
{
bodyOrLeave = bodyBlock;
return true;
}
return false;
}
/// <summary>
/// call get_Length(ldloc switchValueVar)
/// </summary>
bool MatchStringLengthCall(ILInstruction inst, ILVariable switchValueVar)
{
return inst is Call call
&& call.Method.DeclaringType.IsKnownType(KnownTypeCode.String)
&& call.Method.IsAccessor
&& call.Method.AccessorKind == System.Reflection.MethodSemanticsAttributes.Getter
&& call.Method.AccessorOwner.Name == "Length"
&& call.Arguments.Count == 1
&& call.Arguments[0].MatchLdLoc(switchValueVar);
}
/// <summary>
/// Matches 'stloc(targetVar, call ComputeStringHash(ldloc switchValue))'
/// </summary>
internal static bool MatchComputeStringHashCall(ILInstruction inst, ILVariable targetVar, out LdLoc switchValue)
{
switchValue = null;
if (!inst.MatchStLoc(targetVar, out var value))
return false;
if (!(value is Call c && c.Arguments.Count == 1 && c.Method.Name == "ComputeStringHash" && c.Method.IsCompilerGeneratedOrIsInCompilerGeneratedClass()))
return false;
if (!(c.Arguments[0] is LdLoc))
return false;
switchValue = (LdLoc)c.Arguments[0];
return true;
}
/// <summary>
/// Matches 'call string.op_Equality(ldloc(variable), ldstr(stringValue))'
/// or 'comp(ldloc(variable) == ldnull)'
/// </summary>
bool MatchStringEqualityComparison(ILInstruction condition, ILVariable variable, out string stringValue, out bool isVBCompareString)
{
return MatchStringEqualityComparison(condition, out var v, out stringValue, out isVBCompareString) && v == variable;
}
/// <summary>
/// Matches 'call string.op_Equality(ldloc(variable), ldstr(stringValue))'
/// or 'comp(ldloc(variable) == ldnull)'
/// </summary>
bool MatchStringEqualityComparison(ILInstruction condition, out ILVariable variable, out string stringValue, out bool isVBCompareString)
{
stringValue = null;
variable = null;
isVBCompareString = false;
while (condition is Comp comp && comp.Kind == ComparisonKind.Inequality && comp.Right.MatchLdcI4(0))
{
// if (x != 0) == if (x)
condition = comp.Left;
}
if (condition is Call c)
{
ILInstruction left, right;
if (c.Method.IsOperator && c.Method.Name == "op_Equality"
&& c.Method.DeclaringType.IsKnownType(KnownTypeCode.String) && c.Arguments.Count == 2)
{
left = c.Arguments[0];
right = c.Arguments[1];
}
else if (c.Method.IsStatic && c.Method.Name == "CompareString"
&& c.Method.DeclaringType.FullName == "Microsoft.VisualBasic.CompilerServices.Operators"
&& c.Arguments.Count == 3)
{
left = c.Arguments[0];
right = c.Arguments[1];
// VB CompareString(): return 0 on equality -> condition is effectively negated.
// Also, the empty string is considered equal to null.
isVBCompareString = true;
if (!c.Arguments[2].MatchLdcI4(0))
{
// Option Compare Text: case insensitive comparison is not supported in C#
return false;
}
}
else
{
return false;
}
return left.MatchLdLoc(out variable) && right.MatchLdStr(out stringValue);
}
else if (condition.MatchCompEqualsNull(out var arg))
{
stringValue = null;
return arg.MatchLdLoc(out variable);
}
else
{
return false;
}
}
}
}