private AssignmentStatement <TInstruction> CreateAssignment(
Expression <TInstruction> expression,
TInstruction instruction,
IVariable[] writtenVariables)
{
// We will create stack slots for every push and "simulate" an assignment
// to them. This way the resulting AST won't have the "concept" of a stack.
int pushes = _context.Architecture.GetStackPushCount(instruction);
var slots = GetStackSlots(pushes);
var buffer = new AstVariable[slots.Length + writtenVariables.Length];
slots.CopyTo(buffer.AsSpan());
// Also assign to written variables.
for (int i = 0; i < writtenVariables.Length; i++)
{
// Get the correct version of the variable to assign to.
var variable = writtenVariables[i];
int version = _context.GetVariableVersion(variable);
var snapshot = new VariableSnapshot(variable, version);
var versionedVariable = _context.GetVersionedVariable(snapshot);
buffer[slots.Length + i] = versionedVariable;
}
// Assign stack slots.
_context.StackSlots[instruction] = slots;
return(new AssignmentStatement <TInstruction>(buffer, expression));
}
internal AstVariable GetVersionedVariable(VariableSnapshot snapshot)
{
if (VersionedVariables.TryGetValue(snapshot, out var variable))
{
return(variable);
}
variable = new AstVariable(snapshot.ToString());
VersionedVariables.Add(snapshot, variable);
return(variable);
}
private IVariable[] VersionWrittenVariables(TInstruction instruction)
{
var buffer = GetWrittenVariables(instruction);
foreach (var variable in buffer)
{
if (_context.VariableStates.TryGetValue(instruction, out var states))
{
// If we already have a dictionary that contains versions for this instruction,
// we can reuse the same instance.
// If the instruction hasn't "seen" the variable before, we add a new entry.
if (!states.ContainsKey(variable))
{
states.Add(variable, _context.VariableVersions[variable]++);
}
// Create a new snapshot of the variable and store the versioned variable
// created from the snapshot.
var snapshot = new VariableSnapshot(variable, _context.VariableVersions[variable]);
var versionedVariable = _context.GetVersionedVariable(snapshot);
_context.VersionedVariables[snapshot] = versionedVariable;
}
else
{
// Otherwise we will create a new dictionary and store it so it can be
// reused later.
// Increment the version of the variable, create a snapshot and
// add it to the newly created dictionary.
int version = _context.IncrementVariableVersion(variable);
var snapshot = new VariableSnapshot(variable, version);
states = new Dictionary <IVariable, int>
{
[variable] = version
};
// Save the dictionary for later reuse and get a variable for the snapshot.
_context.VariableStates[instruction] = states;
_context.VersionedVariables[snapshot] = _context.GetVersionedVariable(snapshot);
}
}
return(buffer);
}
private void CollectVariableDependencies(
BasicBlock <Statement <TInstruction> > block,
DataFlowNode <TInstruction> dataFlowNode,
Span <IVariable> buffer,
ref int phiStatementCount)
{
int index = 0;
var variableDependencies = dataFlowNode.VariableDependencies;
foreach (var pair in variableDependencies)
{
var variable = pair.Key;
var dependency = pair.Value;
if (dependency.Count <= 1)
{
// If the dependency has only 1 possible source we just simply
// get the variable. But since the AST utilizes SSA, all of the
// variables are versioned. This is good because everything is
// "immutable". One "real" variable will have a new versioned
// variable created every time it is assigned to.
int version = _context.GetVariableVersion(variable);
var snapshot = new VariableSnapshot(variable, version);
buffer[index++] = _context.GetVersionedVariable(snapshot);
continue;
}
// Otherwise (>0), we will get the list of versioned(!) variables
// that could reach the instruction and create a "phi" statement
// like in the stack dependencies.
var sources = CollectVariables();
if (_context.VariableSourcesToPhiVariable.TryGetValue(sources, out var phi))
{
// If a phi slot already exists for the list of variables,
// reuse the same phi slot.
buffer[index++] = phi;
}
else
{
// Otherwise, create a new phi slot for the list of variables
// and save it if we encounter the same variables again.
phi = CreatePhiSlot();
var slots = sources
.Select(source => new VariableExpression <TInstruction>(source))
.ToArray();
_context.VariableSourcesToPhiVariable.Add(sources, phi);
block.Instructions.Insert(phiStatementCount++, new PhiStatement <TInstruction>(phi, slots));
buffer[index++] = phi;
}
List <AstVariable> CollectVariables()
{
var result = new List <AstVariable>();
foreach (var instruction in dependency.Select(dep => dep.Node.Contents))
{
if (_context.VariableStates.TryGetValue(instruction, out var versions))
{
// If we already have a dictionary for the instruction, we will
// just get the versioned variable from the existing dictionary.
var snapshot = new VariableSnapshot(variable, versions[variable]);
result.Add(_context.VersionedVariables[snapshot]);
}
else
{
// Otherwise, we will create a new dictionary for the instruction.
var snapshot = new VariableSnapshot(variable, 0);
var slot = _context.GetVersionedVariable(snapshot);
_context.VariableStates.Add(instruction, new Dictionary <IVariable, int>
{
[variable] = 0
});
result.Add(slot);
}
}
return(result);
}
}
}
