PeepholeTransform.cs

// Copyright (c) 2011 AlphaSierraPapa for the SharpDevelop Team
// 
// 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.Diagnostics;
using System.Linq;

using ICSharpCode.NRefactory.Utils;
using Mono.Cecil;

namespace ICSharpCode.Decompiler.ILAst
{
	public partial class ILAstOptimizer
	{
		#region TransformDecimalCtorToConstant
		static bool TransformDecimalCtorToConstant(List<ILNode> body, ILExpression expr, int pos)
		{
			MethodReference r;
			List<ILExpression> args;
			if (expr.Match(ILCode.Newobj, out r, out args) &&
			    r.DeclaringType.Namespace == "System" &&
			    r.DeclaringType.Name == "Decimal")
			{
				if (args.Count == 1) {
					int val;
					if (args[0].Match(ILCode.Ldc_I4, out val)) {
						expr.Code = ILCode.Ldc_Decimal;
						expr.Operand = new decimal(val);
						expr.InferredType = r.DeclaringType;
						expr.Arguments.Clear();
						return true;
					}
				} else if (args.Count == 5) {
					int lo, mid, hi, isNegative, scale;
					if (expr.Arguments[0].Match(ILCode.Ldc_I4, out lo) &&
					    expr.Arguments[1].Match(ILCode.Ldc_I4, out mid) &&
					    expr.Arguments[2].Match(ILCode.Ldc_I4, out hi) &&
					    expr.Arguments[3].Match(ILCode.Ldc_I4, out isNegative) &&
					    expr.Arguments[4].Match(ILCode.Ldc_I4, out scale))
					{
						expr.Code = ILCode.Ldc_Decimal;
						expr.Operand = new decimal(lo, mid, hi, isNegative != 0, (byte)scale);
						expr.InferredType = r.DeclaringType;
						expr.Arguments.Clear();
						return true;
					}
				}
			}
			bool modified = false;
			foreach(ILExpression arg in expr.Arguments) {
				modified |= TransformDecimalCtorToConstant(null, arg, -1);
			}
			return modified;
		}
		#endregion
		
		#region SimplifyLdObjAndStObj
		static bool SimplifyLdObjAndStObj(List<ILNode> body, ILExpression expr, int pos)
		{
			bool modified = false;
			expr = SimplifyLdObjAndStObj(expr, ref modified);
			if (modified && body != null)
				body[pos] = expr;
			for (int i = 0; i < expr.Arguments.Count; i++) {
				expr.Arguments[i] = SimplifyLdObjAndStObj(expr.Arguments[i], ref modified);
				modified |= SimplifyLdObjAndStObj(null, expr.Arguments[i], -1);
			}
			return modified;
		}
		
		static ILExpression SimplifyLdObjAndStObj(ILExpression expr, ref bool modified)
		{
			if (expr.Code == ILCode.Initobj) {
				expr.Code = ILCode.Stobj;
				expr.Arguments.Add(new ILExpression(ILCode.DefaultValue, expr.Operand));
				modified = true;
			} else if (expr.Code == ILCode.Cpobj) {
				expr.Code = ILCode.Stobj;
				expr.Arguments[1] = new ILExpression(ILCode.Ldobj, expr.Operand, expr.Arguments[1]);
				modified = true;
			}
			ILExpression arg, arg2;
			TypeReference type;
			ILCode? newCode = null;
			if (expr.Match(ILCode.Stobj, out type, out arg, out arg2)) {
				switch (arg.Code) {
						case ILCode.Ldelema: newCode = ILCode.Stelem_Any; break;
						case ILCode.Ldloca:  newCode = ILCode.Stloc; break;
						case ILCode.Ldflda:  newCode = ILCode.Stfld; break;
						case ILCode.Ldsflda: newCode = ILCode.Stsfld; break;
				}
			} else if (expr.Match(ILCode.Ldobj, out type, out arg)) {
				switch (arg.Code) {
						case ILCode.Ldelema: newCode = ILCode.Ldelem_Any; break;
						case ILCode.Ldloca:  newCode = ILCode.Ldloc; break;
						case ILCode.Ldflda:  newCode = ILCode.Ldfld; break;
						case ILCode.Ldsflda: newCode = ILCode.Ldsfld; break;
				}
			}
			if (newCode != null) {
				arg.Code = newCode.Value;
				if (expr.Code == ILCode.Stobj) {
					arg.InferredType = expr.InferredType;
					arg.ExpectedType = expr.ExpectedType;
					arg.Arguments.Add(arg2);
				}
				arg.ILRanges.AddRange(expr.ILRanges);
				modified = true;
				return arg;
			} else {
				return expr;
			}
		}
		#endregion
		
		#region SimplifyLdcI4ConvI8
		static bool SimplifyLdcI4ConvI8(List<ILNode> body, ILExpression expr, int pos)
		{
			ILExpression ldc;
			int val;
			if (expr.Match(ILCode.Conv_I8, out ldc) && ldc.Match(ILCode.Ldc_I4, out val)) {
				expr.Code = ILCode.Ldc_I8;
				expr.Operand = (long)val;
				expr.Arguments.Clear();
				return true;
			}
			bool modified = false;
			foreach(ILExpression arg in expr.Arguments) {
				modified |= SimplifyLdcI4ConvI8(null, arg, -1);
			}
			return modified;
		}
		#endregion
		
		#region CachedDelegateInitialization
		void CachedDelegateInitializationWithField(ILBlock block, ref int i)
		{
			// if (logicnot(ldsfld(field))) {
			//     stsfld(field, newobj(Action::.ctor, ldnull(), ldftn(method)))
			// } else {
			// }
			// ...(..., ldsfld(field), ...)
			
			ILCondition c = block.Body[i] as ILCondition;
			if (c == null || c.Condition == null && c.TrueBlock == null || c.FalseBlock == null)
				return;
			if (!(c.TrueBlock.Body.Count == 1 && c.FalseBlock.Body.Count == 0))
				return;
			if (!c.Condition.Match(ILCode.LogicNot))
				return;
			ILExpression condition = c.Condition.Arguments.Single() as ILExpression;
			if (condition == null || condition.Code != ILCode.Ldsfld)
				return;
			FieldDefinition field = ((FieldReference)condition.Operand).ResolveWithinSameModule(); // field is defined in current assembly
			if (field == null || !field.IsCompilerGeneratedOrIsInCompilerGeneratedClass())
				return;
			ILExpression stsfld = c.TrueBlock.Body[0] as ILExpression;
			if (!(stsfld != null && stsfld.Code == ILCode.Stsfld && ((FieldReference)stsfld.Operand).ResolveWithinSameModule() == field))
				return;
			ILExpression newObj = stsfld.Arguments[0];
			if (!(newObj.Code == ILCode.Newobj && newObj.Arguments.Count == 2))
				return;
			if (newObj.Arguments[0].Code != ILCode.Ldnull)
				return;
			if (newObj.Arguments[1].Code != ILCode.Ldftn)
				return;
			MethodDefinition anonymousMethod = ((MethodReference)newObj.Arguments[1].Operand).ResolveWithinSameModule(); // method is defined in current assembly
			if (!Ast.Transforms.DelegateConstruction.IsAnonymousMethod(context, anonymousMethod))
				return;
			
			ILNode followingNode = block.Body.ElementAtOrDefault(i + 1);
			if (followingNode != null && followingNode.GetSelfAndChildrenRecursive<ILExpression>().Count(
				e => e.Code == ILCode.Ldsfld && ((FieldReference)e.Operand).ResolveWithinSameModule() == field) == 1)
			{
				foreach (ILExpression parent in followingNode.GetSelfAndChildrenRecursive<ILExpression>()) {
					for (int j = 0; j < parent.Arguments.Count; j++) {
						if (parent.Arguments[j].Code == ILCode.Ldsfld && ((FieldReference)parent.Arguments[j].Operand).ResolveWithinSameModule() == field) {
							parent.Arguments[j] = newObj;
							block.Body.RemoveAt(i);
							i -= new ILInlining(method).InlineInto(block.Body, i, aggressive: false);
							return;
						}
					}
				}
			}
		}
		
		void CachedDelegateInitializationWithLocal(ILBlock block, ref int i)
		{
			// if (logicnot(ldloc(v))) {
			//     stloc(v, newobj(Action::.ctor, ldloc(displayClass), ldftn(method)))
			// } else {
			// }
			// ...(..., ldloc(v), ...)
			
			ILCondition c = block.Body[i] as ILCondition;
			if (c == null || c.Condition == null && c.TrueBlock == null || c.FalseBlock == null)
				return;
			if (!(c.TrueBlock.Body.Count == 1 && c.FalseBlock.Body.Count == 0))
				return;
			if (!c.Condition.Match(ILCode.LogicNot))
				return;
			ILExpression condition = c.Condition.Arguments.Single() as ILExpression;
			if (condition == null || condition.Code != ILCode.Ldloc)
				return;
			ILVariable v = (ILVariable)condition.Operand;
			ILExpression stloc = c.TrueBlock.Body[0] as ILExpression;
			if (!(stloc != null && stloc.Code == ILCode.Stloc && (ILVariable)stloc.Operand == v))
				return;
			ILExpression newObj = stloc.Arguments[0];
			if (!(newObj.Code == ILCode.Newobj && newObj.Arguments.Count == 2))
				return;
			if (newObj.Arguments[0].Code != ILCode.Ldloc)
				return;
			if (newObj.Arguments[1].Code != ILCode.Ldftn)
				return;
			MethodDefinition anonymousMethod = ((MethodReference)newObj.Arguments[1].Operand).ResolveWithinSameModule(); // method is defined in current assembly
			if (!Ast.Transforms.DelegateConstruction.IsAnonymousMethod(context, anonymousMethod))
				return;
			
			ILNode followingNode = block.Body.ElementAtOrDefault(i + 1);
			if (followingNode != null && followingNode.GetSelfAndChildrenRecursive<ILExpression>().Count(
				e => e.Code == ILCode.Ldloc && (ILVariable)e.Operand == v) == 1)
			{
				ILInlining inlining = new ILInlining(method);
				if (!(inlining.numLdloc.GetOrDefault(v) == 2 && inlining.numStloc.GetOrDefault(v) == 2 && inlining.numLdloca.GetOrDefault(v) == 0))
					return;
				
				// Find the store instruction that initializes the local to null:
				foreach (ILBlock storeBlock in method.GetSelfAndChildrenRecursive<ILBlock>()) {
					for (int j = 0; j < storeBlock.Body.Count; j++) {
						ILVariable storedVar;
						ILExpression storedExpr;
						if (storeBlock.Body[j].Match(ILCode.Stloc, out storedVar, out storedExpr) && storedVar == v && storedExpr.Match(ILCode.Ldnull)) {
							// Remove the instruction
							storeBlock.Body.RemoveAt(j);
							if (storeBlock == block && j < i)
								i--;
							break;
						}
					}
				}
				
				block.Body[i] = stloc; // remove the 'if (v==null)'
				inlining = new ILInlining(method);
				inlining.InlineIfPossible(block.Body, ref i);
			}
		}
		#endregion
		
		#region MakeAssignmentExpression
		bool MakeAssignmentExpression(List<ILNode> body, ILExpression expr, int pos)
		{
			// exprVar = ...
			// stloc(v, exprVar)
			// ->
			// exprVar = stloc(v, ...))
			ILVariable exprVar;
			ILExpression initializer;
			if (!(expr.Match(ILCode.Stloc, out exprVar, out initializer) && exprVar.IsGenerated))
				return false;
			ILExpression nextExpr = body.ElementAtOrDefault(pos + 1) as ILExpression;
			ILVariable v;
			ILExpression stLocArg;
			if (nextExpr.Match(ILCode.Stloc, out v, out stLocArg) && stLocArg.MatchLdloc(exprVar)) {
				ILExpression store2 = body.ElementAtOrDefault(pos + 2) as ILExpression;
				if (StoreCanBeConvertedToAssignment(store2, exprVar)) {
					// expr_44 = ...
					// stloc(v1, expr_44)
					// anystore(v2, expr_44)
					// ->
					// stloc(v1, anystore(v2, ...))
					ILInlining inlining = new ILInlining(method);
					if (inlining.numLdloc.GetOrDefault(exprVar) == 2 && inlining.numStloc.GetOrDefault(exprVar) == 1) {
						body.RemoveAt(pos + 2); // remove store2
						body.RemoveAt(pos); // remove expr = ...
						nextExpr.Arguments[0] = store2;
						store2.Arguments[store2.Arguments.Count - 1] = initializer;
						
						inlining.InlineIfPossible(body, ref pos);
						
						return true;
					}
				}
				
				body.RemoveAt(pos + 1); // remove stloc
				nextExpr.Arguments[0] = initializer;
				((ILExpression)body[pos]).Arguments[0] = nextExpr;
				return true;
			} else if ((nextExpr.Code == ILCode.Stsfld || nextExpr.Code == ILCode.CallSetter || nextExpr.Code == ILCode.CallvirtSetter) && nextExpr.Arguments.Count == 1) {
				// exprVar = ...
				// stsfld(fld, exprVar)
				// ->
				// exprVar = stsfld(fld, ...))
				if (nextExpr.Arguments[0].MatchLdloc(exprVar)) {
					body.RemoveAt(pos + 1); // remove stsfld
					nextExpr.Arguments[0] = initializer;
					((ILExpression)body[pos]).Arguments[0] = nextExpr;
					return true;
				}
			}
			return false;
		}
		
		bool StoreCanBeConvertedToAssignment(ILExpression store, ILVariable exprVar)
		{
			if (store == null)
				return false;
			switch (store.Code) {
				case ILCode.Stloc:
				case ILCode.Stfld:
				case ILCode.Stsfld:
				case ILCode.Stobj:
				case ILCode.CallSetter:
				case ILCode.CallvirtSetter:
					break;
				default:
					if (!store.Code.IsStoreToArray())
						return false;
					break;
			}
			return store.Arguments.Last().Code == ILCode.Ldloc && store.Arguments.Last().Operand == exprVar;
		}
		#endregion
		
		#region MakeCompoundAssignments
		bool MakeCompoundAssignments(List<ILNode> body, ILExpression expr, int pos)
		{
			bool modified = false;
			modified |= MakeCompoundAssignment(expr);
			// Static fields and local variables are not handled here - those are expressions without side effects
			// and get handled by ReplaceMethodCallsWithOperators
			// (which does a reversible transform to the short operator form, as the introduction of checked/unchecked might have to revert to the long form).
			foreach (ILExpression arg in expr.Arguments) {
				modified |= MakeCompoundAssignments(null, arg, -1);
			}
			if (modified && body != null)
				new ILInlining(method).InlineInto(body, pos, aggressive: false);
			return modified;
		}
		
		bool MakeCompoundAssignment(ILExpression expr)
		{
			// stelem.any(T, ldloc(array), ldloc(pos), <OP>(ldelem.any(T, ldloc(array), ldloc(pos)), <RIGHT>))
			// or
			// stobj(T, ldloc(ptr), <OP>(ldobj(T, ldloc(ptr)), <RIGHT>))
			ILCode expectedLdelemCode;
			switch (expr.Code) {
				case ILCode.Stelem_Any:
					expectedLdelemCode = ILCode.Ldelem_Any;
					break;
				case ILCode.Stfld:
					expectedLdelemCode = ILCode.Ldfld;
					break;
				case ILCode.Stobj:
					expectedLdelemCode = ILCode.Ldobj;
					break;
				case ILCode.CallSetter:
					expectedLdelemCode = ILCode.CallGetter;
					break;
				case ILCode.CallvirtSetter:
					expectedLdelemCode = ILCode.CallvirtGetter;
					break;
				default:
					return false;
			}
			
			// all arguments except the last (so either array+pos, or ptr):
			bool hasGeneratedVar = false;
			for (int i = 0; i < expr.Arguments.Count - 1; i++) {
				ILVariable inputVar;
				if (!expr.Arguments[i].Match(ILCode.Ldloc, out inputVar))
					return false;
				hasGeneratedVar |= inputVar.IsGenerated;
			}
			// At least one of the variables must be generated; otherwise we just keep the expanded form.
			// We do this because we want compound assignments to be represented in ILAst only when strictly necessary;
			// other compound assignments will be introduced by ReplaceMethodCallsWithOperator
			// (which uses a reversible transformation, see ReplaceMethodCallsWithOperator.RestoreOriginalAssignOperatorAnnotation)
			if (!hasGeneratedVar)
				return false;
			
			ILExpression op = expr.Arguments.Last();
			if (!CanBeRepresentedAsCompoundAssignment(op.Code))
				return false;
			ILExpression ldelem = op.Arguments[0];
			if (ldelem.Code != expectedLdelemCode)
				return false;
			Debug.Assert(ldelem.Arguments.Count == expr.Arguments.Count - 1);
			for (int i = 0; i < ldelem.Arguments.Count; i++) {
				if (!ldelem.Arguments[i].MatchLdloc((ILVariable)expr.Arguments[i].Operand))
					return false;
			}
			expr.Code = ILCode.CompoundAssignment;
			expr.Operand = null;
			expr.Arguments.RemoveRange(0, ldelem.Arguments.Count);
			// result is "CompoundAssignment(<OP>(ldelem.any(...), <RIGHT>))"
			return true;
		}
		
		static bool CanBeRepresentedAsCompoundAssignment(ILCode code)
		{
			switch (code) {
				case ILCode.Add:
				case ILCode.Add_Ovf:
				case ILCode.Add_Ovf_Un:
				case ILCode.Sub:
				case ILCode.Sub_Ovf:
				case ILCode.Sub_Ovf_Un:
				case ILCode.Mul:
				case ILCode.Mul_Ovf:
				case ILCode.Mul_Ovf_Un:
				case ILCode.Div:
				case ILCode.Div_Un:
				case ILCode.Rem:
				case ILCode.Rem_Un:
				case ILCode.And:
				case ILCode.Or:
				case ILCode.Xor:
				case ILCode.Shl:
				case ILCode.Shr:
				case ILCode.Shr_Un:
					return true;
				default:
					return false;
			}
		}
		#endregion
		
		#region IntroducePostIncrement

		bool IntroducePostIncrement(List<ILNode> body, ILExpression expr, int pos)
		{
			bool modified = IntroducePostIncrementForVariables(body, expr, pos);
			Debug.Assert(body[pos] == expr); // IntroducePostIncrementForVariables shouldn't change the expression reference
			ILExpression newExpr = IntroducePostIncrementForInstanceFields(expr);
			if (newExpr != null) {
				modified = true;
				body[pos] = newExpr;
				new ILInlining(method).InlineIfPossible(body, ref pos);
			}
			return modified;
		}

		bool IntroducePostIncrementForVariables(List<ILNode> body, ILExpression expr, int pos)
		{
			// Works for variables and static fields/properties
			
			// expr = ldloc(i)
			// stloc(i, add(expr, ldc.i4(1)))
			// ->
			// expr = postincrement(1, ldloca(i))
			ILVariable exprVar;
			ILExpression exprInit;
			if (!(expr.Match(ILCode.Stloc, out exprVar, out exprInit) && exprVar.IsGenerated))
				return false;
			
			//The next expression
			ILExpression nextExpr = body.ElementAtOrDefault(pos + 1) as ILExpression;
			if (nextExpr == null)
				return false;
			
			ILCode loadInstruction = exprInit.Code;
			ILCode storeInstruction = nextExpr.Code;
			bool recombineVariable = false;
			
			// We only recognise local variables, static fields, and static getters with no arguments
			switch (loadInstruction) {
				case ILCode.Ldloc:
					//Must be a matching store type
					if (storeInstruction != ILCode.Stloc)
						return false;
					ILVariable loadVar = (ILVariable)exprInit.Operand;
					ILVariable storeVar = (ILVariable)nextExpr.Operand;
					if (loadVar != storeVar) {
						if (loadVar.OriginalVariable != null && loadVar.OriginalVariable == storeVar.OriginalVariable)
							recombineVariable = true;
						else
							return false;
					}
					break;
				case ILCode.Ldsfld:
					if (storeInstruction != ILCode.Stsfld)
						return false;
					if (exprInit.Operand != nextExpr.Operand)
						return false;
					break;
				case ILCode.CallGetter:
					// non-static getters would have the 'this' argument
					if (exprInit.Arguments.Count != 0)
						return false;
					if (storeInstruction != ILCode.CallSetter)
						return false;
					if (!IsGetterSetterPair(exprInit.Operand, nextExpr.Operand))
						return false;
					break;
				default:
					return false;
			}
			
			ILExpression addExpr = nextExpr.Arguments[0];
			
			int incrementAmount;
			ILCode incrementCode = GetIncrementCode(addExpr, out incrementAmount);
			if (!(incrementAmount != 0 && addExpr.Arguments[0].MatchLdloc(exprVar)))
				return false;
			
			if (recombineVariable) {
				// Split local variable, unsplit these two instances
				// replace nextExpr.Operand with exprInit.Operand
				ReplaceVariables(method, oldVar => oldVar == nextExpr.Operand ? (ILVariable)exprInit.Operand : oldVar);
			}
			
			switch (loadInstruction) {
				case ILCode.Ldloc:
					exprInit.Code = ILCode.Ldloca;
					break;
				case ILCode.Ldsfld:
					exprInit.Code = ILCode.Ldsflda;
					break;
				case ILCode.CallGetter:
					exprInit = new ILExpression(ILCode.AddressOf, null, exprInit);
					break;
			}
			expr.Arguments[0] = new ILExpression(incrementCode, incrementAmount, exprInit);
			body.RemoveAt(pos + 1); // TODO ILRanges
			return true;
		}
		
		static bool IsGetterSetterPair(object getterOperand, object setterOperand)
		{
			MethodReference getter = getterOperand as MethodReference;
			MethodReference setter = setterOperand as MethodReference;
			if (getter == null || setter == null)
				return false;
			if (!TypeAnalysis.IsSameType(getter.DeclaringType, setter.DeclaringType))
				return false;
			MethodDefinition getterDef = getter.Resolve();
			MethodDefinition setterDef = setter.Resolve();
			if (getterDef == null || setterDef == null)
				return false;
			foreach (PropertyDefinition prop in getterDef.DeclaringType.Properties) {
				if (prop.GetMethod == getterDef)
					return prop.SetMethod == setterDef;
			}
			return false;
		}
		
		ILExpression IntroducePostIncrementForInstanceFields(ILExpression expr)
		{
			// stfld(field, ldloc(instance), add(stloc(helperVar, ldfld(field, ldloc(instance))), ldc.i4(1)))
			// -> stloc(helperVar, postincrement(1, ldflda(field, ldloc(instance))))
			
			// Also works for array elements and pointers:
			
			// stelem.any(T, ldloc(instance), ldloc(pos), add(stloc(helperVar, ldelem.any(T, ldloc(instance), ldloc(pos))), ldc.i4(1)))
			// -> stloc(helperVar, postincrement(1, ldelema(ldloc(instance), ldloc(pos))))
			
			// stobj(T, ldloc(ptr), add(stloc(helperVar, ldobj(T, ldloc(ptr)), ldc.i4(1))))
			// -> stloc(helperVar, postIncrement(1, ldloc(ptr)))
			
			// callsetter(set_P, ldloc(instance), add(stloc(helperVar, callgetter(get_P, ldloc(instance))), ldc.i4(1)))
			// -> stloc(helperVar, postIncrement(1, propertyaddress. callgetter(get_P, ldloc(instance))))
			
			if (!(expr.Code == ILCode.Stfld || expr.Code.IsStoreToArray() || expr.Code == ILCode.Stobj || expr.Code == ILCode.CallSetter || expr.Code == ILCode.CallvirtSetter))
				return null;
			
			// Test that all arguments except the last are ldloc (1 arg for fields and pointers, 2 args for arrays)
			for (int i = 0; i < expr.Arguments.Count - 1; i++) {
				if (expr.Arguments[i].Code != ILCode.Ldloc)
					return null;
			}
			
			ILExpression addExpr = expr.Arguments[expr.Arguments.Count - 1];
			int incrementAmount;
			ILCode incrementCode = GetIncrementCode(addExpr, out incrementAmount);
			ILVariable helperVar;
			ILExpression initialValue;
			if (!(incrementAmount != 0 && addExpr.Arguments[0].Match(ILCode.Stloc, out helperVar, out initialValue)))
				return null;
			
			if (expr.Code == ILCode.Stfld) {
				if (initialValue.Code != ILCode.Ldfld)
					return null;
				// There might be two different FieldReference instances, so we compare the field's signatures:
				FieldReference getField = (FieldReference)initialValue.Operand;
				FieldReference setField = (FieldReference)expr.Operand;
				if (!(TypeAnalysis.IsSameType(getField.DeclaringType, setField.DeclaringType)
				      && getField.Name == setField.Name && TypeAnalysis.IsSameType(getField.FieldType, setField.FieldType)))
				{
					return null;
				}
			} else if (expr.Code == ILCode.Stobj) {
				if (!(initialValue.Code == ILCode.Ldobj && initialValue.Operand == expr.Operand))
					return null;
			} else if (expr.Code == ILCode.CallSetter) {
				if (!(initialValue.Code == ILCode.CallGetter && IsGetterSetterPair(initialValue.Operand, expr.Operand)))
					return null;
			} else if (expr.Code == ILCode.CallvirtSetter) {
				if (!(initialValue.Code == ILCode.CallvirtGetter && IsGetterSetterPair(initialValue.Operand, expr.Operand)))
					return null;
			} else {
				if (!initialValue.Code.IsLoadFromArray())
					return null;
			}
			Debug.Assert(expr.Arguments.Count - 1 == initialValue.Arguments.Count);
			for (int i = 0; i < initialValue.Arguments.Count; i++) {
				if (!initialValue.Arguments[i].MatchLdloc((ILVariable)expr.Arguments[i].Operand))
					return null;
			}
			
			ILExpression stloc = addExpr.Arguments[0];
			if (expr.Code == ILCode.Stobj) {
				stloc.Arguments[0] = new ILExpression(ILCode.PostIncrement, incrementAmount, initialValue.Arguments[0]);
			} else if (expr.Code == ILCode.CallSetter || expr.Code == ILCode.CallvirtSetter) {
				initialValue = new ILExpression(ILCode.AddressOf, null, initialValue);
				stloc.Arguments[0] = new ILExpression(ILCode.PostIncrement, incrementAmount, initialValue);
			} else {
				stloc.Arguments[0] = new ILExpression(ILCode.PostIncrement, incrementAmount, initialValue);
				initialValue.Code = (expr.Code == ILCode.Stfld ? ILCode.Ldflda : ILCode.Ldelema);
			}
			// TODO: ILRanges?
			
			return stloc;
		}
		
		ILCode GetIncrementCode(ILExpression addExpr, out int incrementAmount)
		{
			ILCode incrementCode;
			bool decrement = false;
			switch (addExpr.Code) {
				case ILCode.Add:
					incrementCode = ILCode.PostIncrement;
					break;
				case ILCode.Add_Ovf:
					incrementCode = ILCode.PostIncrement_Ovf;
					break;
				case ILCode.Add_Ovf_Un:
					incrementCode = ILCode.PostIncrement_Ovf_Un;
					break;
				case ILCode.Sub:
					incrementCode = ILCode.PostIncrement;
					decrement = true;
					break;
				case ILCode.Sub_Ovf:
					incrementCode = ILCode.PostIncrement_Ovf;
					decrement = true;
					break;
				case ILCode.Sub_Ovf_Un:
					incrementCode = ILCode.PostIncrement_Ovf_Un;
					decrement = true;
					break;
				default:
					incrementAmount = 0;
					return ILCode.Nop;
			}
			if (addExpr.Arguments[1].Match(ILCode.Ldc_I4, out incrementAmount)) {
				if (incrementAmount == -1 || incrementAmount == 1) { // TODO pointer increment?
					if (decrement)
						incrementAmount = -incrementAmount;
					return incrementCode;
				}
			}
			incrementAmount = 0;
			return ILCode.Nop;
		}
		#endregion
		
		#region IntroduceFixedStatements
		bool IntroduceFixedStatements(List<ILNode> body, int i)
		{
			ILExpression initValue;
			ILVariable pinnedVar;
			int initEndPos;
			if (!MatchFixedInitializer(body, i, out pinnedVar, out initValue, out initEndPos))
				return false;
			
			ILFixedStatement fixedStmt = body.ElementAtOrDefault(initEndPos) as ILFixedStatement;
			if (fixedStmt != null) {
				ILExpression expr = fixedStmt.BodyBlock.Body.LastOrDefault() as ILExpression;
				if (expr != null && expr.Code == ILCode.Stloc && expr.Operand == pinnedVar && IsNullOrZero(expr.Arguments[0])) {
					// we found a second initializer for the existing fixed statement
					fixedStmt.Initializers.Insert(0, initValue);
					body.RemoveRange(i, initEndPos - i);
					fixedStmt.BodyBlock.Body.RemoveAt(fixedStmt.BodyBlock.Body.Count - 1);
					if (pinnedVar.Type.IsByReference)
						pinnedVar.Type = new PointerType(((ByReferenceType)pinnedVar.Type).ElementType);
					return true;
				}
			}
			
			// find where pinnedVar is reset to 0:
			int j;
			for (j = initEndPos; j < body.Count; j++) {
				ILVariable v2;
				ILExpression storedVal;
				// stloc(pinned_Var, conv.u(ldc.i4(0)))
				if (body[j].Match(ILCode.Stloc, out v2, out storedVal) && v2 == pinnedVar) {
					if (IsNullOrZero(storedVal)) {
						break;
					}
				}
			}
			// Create fixed statement from i to j
			fixedStmt = new ILFixedStatement();
			fixedStmt.Initializers.Add(initValue);
			fixedStmt.BodyBlock = new ILBlock(body.GetRange(initEndPos, j - initEndPos)); // from initEndPos to j-1 (inclusive)
			body.RemoveRange(i + 1, Math.Min(j, body.Count - 1) - i); // from i+1 to j (inclusive)
			body[i] = fixedStmt;
			if (pinnedVar.Type.IsByReference)
				pinnedVar.Type = new PointerType(((ByReferenceType)pinnedVar.Type).ElementType);
			
			return true;
		}
		
		bool IsNullOrZero(ILExpression expr)
		{
			if (expr.Code == ILCode.Conv_U || expr.Code == ILCode.Conv_I)
				expr = expr.Arguments[0];
			return (expr.Code == ILCode.Ldc_I4 && (int)expr.Operand == 0) || expr.Code == ILCode.Ldnull;
		}
		
		bool MatchFixedInitializer(List<ILNode> body, int i, out ILVariable pinnedVar, out ILExpression initValue, out int nextPos)
		{
			if (body[i].Match(ILCode.Stloc, out pinnedVar, out initValue) && pinnedVar.IsPinned && !IsNullOrZero(initValue)) {
				initValue = (ILExpression)body[i];
				nextPos = i + 1;
				HandleStringFixing(pinnedVar, body, ref nextPos, ref initValue);
				return true;
			}
			ILCondition ifStmt = body[i] as ILCondition;
			ILExpression arrayLoadingExpr;
			if (ifStmt != null && MatchFixedArrayInitializerCondition(ifStmt.Condition, out arrayLoadingExpr)) {
				ILVariable arrayVariable = (ILVariable)arrayLoadingExpr.Operand;
				ILExpression trueValue;
				if (ifStmt.TrueBlock != null && ifStmt.TrueBlock.Body.Count == 1
				    && ifStmt.TrueBlock.Body[0].Match(ILCode.Stloc, out pinnedVar, out trueValue)
				    && pinnedVar.IsPinned && IsNullOrZero(trueValue))
				{
					if (ifStmt.FalseBlock != null && ifStmt.FalseBlock.Body.Count == 1 && ifStmt.FalseBlock.Body[0] is ILFixedStatement) {
						ILFixedStatement fixedStmt = (ILFixedStatement)ifStmt.FalseBlock.Body[0];
						ILVariable stlocVar;
						ILExpression falseValue;
						if (fixedStmt.Initializers.Count == 1 && fixedStmt.BodyBlock.Body.Count == 0
						    && fixedStmt.Initializers[0].Match(ILCode.Stloc, out stlocVar, out falseValue) && stlocVar == pinnedVar)
						{
							ILVariable loadedVariable;
							if (falseValue.Code == ILCode.Ldelema
							    && falseValue.Arguments[0].Match(ILCode.Ldloc, out loadedVariable) && loadedVariable == arrayVariable
							    && IsNullOrZero(falseValue.Arguments[1]))
							{
								// OK, we detected the pattern for fixing an array.
								// Now check whether the loading expression was a store ot a temp. var
								// that can be eliminated.
								if (arrayLoadingExpr.Code == ILCode.Stloc) {
									ILInlining inlining = new ILInlining(method);
									if (inlining.numLdloc.GetOrDefault(arrayVariable) == 2 &&
									    inlining.numStloc.GetOrDefault(arrayVariable) == 1 && inlining.numLdloca.GetOrDefault(arrayVariable) == 0)
									{
										arrayLoadingExpr = arrayLoadingExpr.Arguments[0];
									}
								}
								initValue = new ILExpression(ILCode.Stloc, pinnedVar, arrayLoadingExpr);
								nextPos = i + 1;
								return true;
							}
						}
					}
				}
			}
			initValue = null;
			nextPos = -1;
			return false;
		}
		
		bool MatchFixedArrayInitializerCondition(ILExpression condition, out ILExpression initValue)
		{
			ILExpression logicAnd;
			ILVariable arrayVar;
			if (condition.Match(ILCode.LogicNot, out logicAnd) && logicAnd.Code == ILCode.LogicAnd) {
				initValue = UnpackDoubleNegation(logicAnd.Arguments[0]);
				ILExpression arrayVarInitializer;
				if (initValue.Match(ILCode.Ldloc, out arrayVar)
				    || initValue.Match(ILCode.Stloc, out arrayVar, out arrayVarInitializer))
				{
					ILExpression arrayLength = logicAnd.Arguments[1];
					if (arrayLength.Code == ILCode.Conv_I4)
						arrayLength = arrayLength.Arguments[0];
					return arrayLength.Code == ILCode.Ldlen && arrayLength.Arguments[0].MatchLdloc(arrayVar);
				}
			}
			initValue = null;
			return false;
		}
		
		ILExpression UnpackDoubleNegation(ILExpression expr)
		{
			ILExpression negated;
			if (expr.Match(ILCode.LogicNot, out negated) && negated.Match(ILCode.LogicNot, out negated))
				return negated;
			else
				return expr;
		}
		
		bool HandleStringFixing(ILVariable pinnedVar, List<ILNode> body, ref int pos, ref ILExpression fixedStmtInitializer)
		{
			// fixed (stloc(pinnedVar, ldloc(text))) {
			//   var1 = var2 = conv.i(ldloc(pinnedVar))
			//   if (logicnot(logicnot(var1))) {
			//     var2 = add(var1, call(RuntimeHelpers::get_OffsetToStringData))
			//   }
			//   stloc(ptrVar, var2)
			//   ...
			
			if (pos >= body.Count)
				return false;
			
			ILVariable var1, var2;
			ILExpression varAssignment, ptrInitialization;
			if (!(body[pos].Match(ILCode.Stloc, out var1, out varAssignment) && varAssignment.Match(ILCode.Stloc, out var2, out ptrInitialization)))
				return false;
			if (!(var1.IsGenerated && var2.IsGenerated))
				return false;
			if (ptrInitialization.Code == ILCode.Conv_I || ptrInitialization.Code == ILCode.Conv_U)
				ptrInitialization = ptrInitialization.Arguments[0];
			if (!ptrInitialization.MatchLdloc(pinnedVar))
				return false;
			
			ILCondition ifStmt = body[pos + 1] as ILCondition;
			if (!(ifStmt != null && ifStmt.TrueBlock != null && ifStmt.TrueBlock.Body.Count == 1 && (ifStmt.FalseBlock == null || ifStmt.FalseBlock.Body.Count == 0)))
				return false;
			if (!UnpackDoubleNegation(ifStmt.Condition).MatchLdloc(var1))
				return false;
			ILVariable assignedVar;
			ILExpression assignedExpr;
			if (!(ifStmt.TrueBlock.Body[0].Match(ILCode.Stloc, out assignedVar, out assignedExpr) && assignedVar == var2 && assignedExpr.Code == ILCode.Add))
				return false;
			MethodReference calledMethod;
			if (!(assignedExpr.Arguments[0].MatchLdloc(var1)))
				return false;
			if (!(assignedExpr.Arguments[1].Match(ILCode.Call, out calledMethod) || assignedExpr.Arguments[1].Match(ILCode.CallGetter, out calledMethod)))
				return false;
			if (!(calledMethod.Name == "get_OffsetToStringData" && calledMethod.DeclaringType.FullName == "System.Runtime.CompilerServices.RuntimeHelpers"))
				return false;
			
			ILVariable pointerVar;
			if (body[pos + 2].Match(ILCode.Stloc, out pointerVar, out assignedExpr) && assignedExpr.MatchLdloc(var2)) {
				pos += 3;
				fixedStmtInitializer.Operand = pointerVar;
				return true;
			}
			return false;
		}
		#endregion
		
		#region SimplifyShiftOperators
		static bool SimplifyShiftOperators(List<ILNode> body, ILExpression expr, int pos)
		{
			// C# compiles "a << b" to "a << (b & 31)", so we will remove the "& 31" if possible.
			bool modified = false;
			SimplifyShiftOperators(expr, ref modified);
			return modified;
		}

		static void SimplifyShiftOperators(ILExpression expr, ref bool modified)
		{
			for (int i = 0; i < expr.Arguments.Count; i++) 
				SimplifyShiftOperators(expr.Arguments[i], ref modified);
			if (expr.Code != ILCode.Shl && expr.Code != ILCode.Shr && expr.Code != ILCode.Shr_Un) 
				return;
			var a = expr.Arguments[1];
			if (a.Code != ILCode.And || a.Arguments[1].Code != ILCode.Ldc_I4 || expr.InferredType == null) 
				return;
			int mask;
			switch (expr.InferredType.MetadataType) {
				case MetadataType.Int32:
				case MetadataType.UInt32: mask = 31; break;
				case MetadataType.Int64:
				case MetadataType.UInt64: mask = 63; break;
				default: return;
			}
			if ((int)a.Arguments[1].Operand != mask) return;
			var res = a.Arguments[0];
			res.ILRanges.AddRange(a.ILRanges);
			res.ILRanges.AddRange(a.Arguments[1].ILRanges);
			expr.Arguments[1] = res;
			modified = true;
		}
		#endregion
	}
}