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// 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 Mono.Cecil;
using Mono.Cecil.Cil;
namespace ICSharpCode.Decompiler.FlowAnalysis
{
/// <summary>
/// This is a transformation working on SSA form.
/// It removes ldloca instructions and replaces them with SpecialOpCode.PrepareByOutCall or SpecialOpCode.PrepareByRefCall.
/// This then allows the variable that had its address taken to also be transformed into SSA.
/// </summary>
sealed class SimplifyByRefCalls
{
public static bool MakeByRefCallsSimple(SsaForm ssaForm)
{
SimplifyByRefCalls instance = new SimplifyByRefCalls(ssaForm);
foreach (SsaBlock block in ssaForm.Blocks) {
for (int i = 0; i < block.Instructions.Count; i++) {
SsaInstruction inst = block.Instructions[i];
if (inst.Instruction != null) {
switch (inst.Instruction.OpCode.Code) {
case Code.Call:
case Code.Callvirt:
instance.MakeByRefCallSimple(block, ref i, (IMethodSignature)inst.Instruction.Operand);
break;
case Code.Initobj:
instance.MakeInitObjCallSimple(block, ref i);
break;
case Code.Ldfld:
instance.MakeLoadFieldCallSimple(block, ref i);
break;
}
}
}
}
instance.RemoveRedundantInstructions();
if (instance.couldSimplifySomething)
ssaForm.ComputeVariableUsage();
return instance.couldSimplifySomething;
}
readonly SsaForm ssaForm;
bool couldSimplifySomething;
// the list of ldloca instructions we will remove
readonly List<SsaInstruction> redundantLoadAddressInstructions = new List<SsaInstruction>();
private SimplifyByRefCalls(SsaForm ssaForm)
{
this.ssaForm = ssaForm;
}
void MakeByRefCallSimple(SsaBlock block, ref int instructionIndexInBlock, IMethodSignature targetMethod)
{
SsaInstruction inst = block.Instructions[instructionIndexInBlock];
for (int i = 0; i < inst.Operands.Length; i++) {
SsaVariable operand = inst.Operands[i];
if (operand.IsSingleAssignment && operand.Usage.Count == 1 && IsLoadAddress(operand.Definition)) {
// address is used for this method call only
Instruction loadAddressInstruction = operand.Definition.Instruction;
// find target parameter type:
bool isOut;
if (i == 0 && targetMethod.HasThis) {
isOut = false;
} else {
ParameterDefinition parameter = targetMethod.Parameters[i - (targetMethod.HasThis ? 1 : 0)];
isOut = parameter.IsOut;
}
SsaVariable addressTakenOf = GetVariableFromLoadAddressInstruction(loadAddressInstruction);
// insert "Prepare" instruction on front
SpecialOpCode loadOpCode = isOut ? SpecialOpCode.PrepareByOutCall : SpecialOpCode.PrepareByRefCall;
block.Instructions.Insert(instructionIndexInBlock++, new SsaInstruction(
block, null, operand, new SsaVariable[] { addressTakenOf }, specialOpCode: loadOpCode));
// insert "WriteAfterByRefOrOutCall" instruction after call
block.Instructions.Insert(instructionIndexInBlock + 1, new SsaInstruction(
block, null, addressTakenOf, new SsaVariable[] { operand }, specialOpCode: SpecialOpCode.WriteAfterByRefOrOutCall));
couldSimplifySomething = true;
// remove the loadAddressInstruction later
// (later because it might be defined in the current block and we don't want instructionIndex to become invalid)
redundantLoadAddressInstructions.Add(operand.Definition);
}
}
}
SsaVariable GetVariableFromLoadAddressInstruction(Instruction loadAddressInstruction)
{
if (loadAddressInstruction.OpCode == OpCodes.Ldloca) {
return ssaForm.GetOriginalVariable((VariableReference)loadAddressInstruction.Operand);
} else {
Debug.Assert(loadAddressInstruction.OpCode == OpCodes.Ldarga);
return ssaForm.GetOriginalVariable((ParameterReference)loadAddressInstruction.Operand);
}
}
static bool IsLoadAddress(SsaInstruction inst)
{
return inst.Instruction != null && (inst.Instruction.OpCode == OpCodes.Ldloca || inst.Instruction.OpCode == OpCodes.Ldarga);
}
void MakeInitObjCallSimple(SsaBlock block, ref int instructionIndexInBlock)
{
SsaInstruction inst = block.Instructions[instructionIndexInBlock];
Debug.Assert(inst.Operands.Length == 1);
SsaVariable operand = inst.Operands[0];
if (operand.IsSingleAssignment && operand.Usage.Count == 1 && IsLoadAddress(operand.Definition)) {
// replace instruction with special "InitObj" instruction
block.Instructions[instructionIndexInBlock] = new SsaInstruction(
inst.ParentBlock, null, GetVariableFromLoadAddressInstruction(operand.Definition.Instruction), null,
specialOpCode: SpecialOpCode.InitObj,
typeOperand: (TypeReference)inst.Instruction.Operand);
couldSimplifySomething = true;
// remove the loadAddressInstruction later
redundantLoadAddressInstructions.Add(operand.Definition);
}
}
void MakeLoadFieldCallSimple(SsaBlock block, ref int instructionIndexInBlock)
{
SsaInstruction inst = block.Instructions[instructionIndexInBlock];
Debug.Assert(inst.Operands.Length == 1);
SsaVariable operand = inst.Operands[0];
if (operand.IsSingleAssignment && operand.Usage.Count == 1 && IsLoadAddress(operand.Definition)) {
// insert special "PrepareForFieldAccess" instruction in front
block.Instructions.Insert(instructionIndexInBlock++, new SsaInstruction(
inst.ParentBlock, null, operand,
new SsaVariable[] { GetVariableFromLoadAddressInstruction(operand.Definition.Instruction) },
specialOpCode: SpecialOpCode.PrepareForFieldAccess));
couldSimplifySomething = true;
// remove the loadAddressInstruction later
redundantLoadAddressInstructions.Add(operand.Definition);
}
}
void RemoveRedundantInstructions()
{
foreach (SsaInstruction inst in redundantLoadAddressInstructions) {
inst.ParentBlock.Instructions.Remove(inst);
}
}
}
}
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