private TransformToSsa(ControlFlowGraph cfg, SsaForm ssaForm)
{
this.cfg = cfg;
this.ssaForm = ssaForm;
this.writeToOriginalVariables = new List<SsaInstruction>[ssaForm.OriginalVariables.Count];
this.addressTaken = new bool[ssaForm.OriginalVariables.Count];
}
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 bool[] addressTaken; // array index -> SsaVariable OriginalVariableIndex; value = whether ldloca instruction was used with variable
TransformToSsa(ControlFlowGraph cfg, SsaForm ssaForm)
{
this.cfg = cfg;
this.ssaForm = ssaForm;
writeToOriginalVariables = new List <SsaInstruction> [ssaForm.OriginalVariables.Count];
addressTaken = new bool[ssaForm.OriginalVariables.Count];
}
internal SsaForm Build()
{
CreateGraphStructure();
this.ssaForm = new SsaForm(blocks, parameters, locals, stackLocations, method.HasThis);
CreateInstructions(cfg.EntryPoint.BlockIndex);
CreateSpecialInstructions();
return(ssaForm);
}
public static void RemoveDeadAssignments(SsaForm ssaForm)
{
HashSet <SsaVariable> liveVariables = new HashSet <SsaVariable>();
// find variables that are used directly
foreach (SsaBlock block in ssaForm.Blocks)
{
foreach (SsaInstruction inst in block.Instructions)
{
if (!CanRemoveAsDeadCode(inst))
{
if (inst.Target != null)
{
liveVariables.Add(inst.Target);
}
foreach (SsaVariable op in inst.Operands)
{
liveVariables.Add(op);
}
}
}
}
Queue <SsaVariable> queue = new Queue <SsaVariable>(liveVariables);
// find variables that are used indirectly
while (queue.Count > 0)
{
SsaVariable v = queue.Dequeue();
if (v.IsSingleAssignment)
{
foreach (SsaVariable op in v.Definition.Operands)
{
if (liveVariables.Add(op))
{
queue.Enqueue(op);
}
}
}
}
// remove assignments to all unused variables
foreach (SsaBlock block in ssaForm.Blocks)
{
block.Instructions.RemoveAll(
inst =>
{
if (inst.Target != null && !liveVariables.Contains(inst.Target))
{
Debug.Assert(inst.Target.IsSingleAssignment);
return(true);
}
return(false);
});
}
ssaForm.ComputeVariableUsage(); // update usage after we modified stuff
}
public static void Transform(ControlFlowGraph cfg, SsaForm ssa, bool optimize = true)
{
TransformToSsa transform = new TransformToSsa(cfg, ssa);
transform.ConvertVariablesToSsa();
SsaOptimization.RemoveDeadAssignments(ssa); // required so that 'MakeByRefCallsSimple' can detect more cases
if (SimplifyByRefCalls.MakeByRefCallsSimple(ssa)) {
transform.ConvertVariablesToSsa();
}
if (optimize)
SsaOptimization.Optimize(ssa);
}
public static void Transform(ControlFlowGraph cfg, SsaForm ssa, bool optimize = true)
{
TransformToSsa transform = new TransformToSsa(cfg, ssa);
transform.ConvertVariablesToSsa();
SsaOptimization.RemoveDeadAssignments(ssa); // required so that 'MakeByRefCallsSimple' can detect more cases
if (SimplifyByRefCalls.MakeByRefCallsSimple(ssa))
{
transform.ConvertVariablesToSsa();
}
if (optimize)
{
SsaOptimization.Optimize(ssa);
}
}
public static void SimpleCopyPropagation(SsaForm ssaForm, bool onlyForStackLocations = true)
{
foreach (SsaBlock block in ssaForm.Blocks) {
foreach (SsaInstruction inst in block.Instructions) {
if (inst.IsMoveInstruction && inst.Target.IsSingleAssignment && inst.Operands[0].IsSingleAssignment) {
if (inst.Target.IsStackLocation || !onlyForStackLocations) {
// replace all uses of 'target' with 'operands[0]'.
foreach (SsaInstruction useInstruction in inst.Target.Usage) {
useInstruction.ReplaceVariableInOperands(inst.Target, inst.Operands[0]);
}
}
}
}
}
ssaForm.ComputeVariableUsage(); // update usage after we modified stuff
}
/// <summary>
/// When any instructions stores its result in a stack location that's used only once in a 'stloc' or 'starg' instruction,
/// we optimize this to directly store in the target location.
/// As optimization this is redundant (does the same as copy propagation), but it'll make us keep the variables named
/// after locals instead of keeping the temps as using only the simple copy propagation would do.
/// </summary>
public static void DirectlyStoreToVariables(SsaForm ssaForm)
{
foreach (SsaBlock block in ssaForm.Blocks) {
block.Instructions.RemoveAll(
inst => {
if (inst.Instruction != null && (inst.Instruction.OpCode == OpCodes.Stloc || inst.Instruction.OpCode == OpCodes.Starg)) {
SsaVariable target = inst.Target;
SsaVariable temp = inst.Operands[0];
if (target.IsSingleAssignment && temp.IsSingleAssignment && temp.Usage.Count == 1 && temp.IsStackLocation) {
temp.Definition.Target = target;
return true;
}
}
return false;
});
}
ssaForm.ComputeVariableUsage(); // update usage after we modified stuff
}
public static void SimpleCopyPropagation(SsaForm ssaForm, bool onlyForStackLocations = true)
{
foreach (SsaBlock block in ssaForm.Blocks)
{
foreach (SsaInstruction inst in block.Instructions)
{
if (inst.IsMoveInstruction && inst.Target.IsSingleAssignment && inst.Operands[0].IsSingleAssignment)
{
if (inst.Target.IsStackLocation || !onlyForStackLocations)
{
// replace all uses of 'target' with 'operands[0]'.
foreach (SsaInstruction useInstruction in inst.Target.Usage)
{
useInstruction.ReplaceVariableInOperands(inst.Target, inst.Operands[0]);
}
}
}
}
}
ssaForm.ComputeVariableUsage(); // update usage after we modified stuff
}
/// <summary>
/// When any instructions stores its result in a stack location that's used only once in a 'stloc' or 'starg' instruction,
/// we optimize this to directly store in the target location.
/// As optimization this is redundant (does the same as copy propagation), but it'll make us keep the variables named
/// after locals instead of keeping the temps as using only the simple copy propagation would do.
/// </summary>
public static void DirectlyStoreToVariables(SsaForm ssaForm)
{
foreach (SsaBlock block in ssaForm.Blocks)
{
block.Instructions.RemoveAll(
inst => {
if (inst.Instruction != null && (inst.Instruction.OpCode == OpCodes.Stloc || inst.Instruction.OpCode == OpCodes.Starg))
{
SsaVariable target = inst.Target;
SsaVariable temp = inst.Operands[0];
if (target.IsSingleAssignment && temp.IsSingleAssignment && temp.Usage.Count == 1 && temp.IsStackLocation)
{
temp.Definition.Target = target;
return(true);
}
}
return(false);
});
}
ssaForm.ComputeVariableUsage(); // update usage after we modified stuff
}
public static void RemoveDeadAssignments(SsaForm ssaForm)
{
HashSet<SsaVariable> liveVariables = new HashSet<SsaVariable>();
// find variables that are used directly
foreach (SsaBlock block in ssaForm.Blocks) {
foreach (SsaInstruction inst in block.Instructions) {
if (!CanRemoveAsDeadCode(inst)) {
if (inst.Target != null)
liveVariables.Add(inst.Target);
foreach (SsaVariable op in inst.Operands) {
liveVariables.Add(op);
}
}
}
}
Queue<SsaVariable> queue = new Queue<SsaVariable>(liveVariables);
// find variables that are used indirectly
while (queue.Count > 0) {
SsaVariable v = queue.Dequeue();
if (v.IsSingleAssignment) {
foreach (SsaVariable op in v.Definition.Operands) {
if (liveVariables.Add(op))
queue.Enqueue(op);
}
}
}
// remove assignments to all unused variables
foreach (SsaBlock block in ssaForm.Blocks) {
block.Instructions.RemoveAll(
inst => {
if (inst.Target != null && !liveVariables.Contains(inst.Target)) {
Debug.Assert(inst.Target.IsSingleAssignment);
return true;
}
return false;
});
}
ssaForm.ComputeVariableUsage(); // update usage after we modified stuff
}
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);
}
internal SsaForm Build()
{
CreateGraphStructure();
this.ssaForm = new SsaForm(blocks, parameters, locals, stackLocations, method.HasThis);
CreateInstructions(cfg.EntryPoint.BlockIndex);
CreateSpecialInstructions();
return ssaForm;
}
public static void Optimize(SsaForm ssaForm)
{
DirectlyStoreToVariables(ssaForm);
SimpleCopyPropagation(ssaForm);
RemoveDeadAssignments(ssaForm);
}
private SimplifyByRefCalls(SsaForm ssaForm)
{
this.ssaForm = ssaForm;
}
private SimplifyByRefCalls(SsaForm ssaForm)
{
this.ssaForm = ssaForm;
}
public static void Optimize(SsaForm ssaForm)
{
DirectlyStoreToVariables(ssaForm);
SimpleCopyPropagation(ssaForm);
RemoveDeadAssignments(ssaForm);
}
