public static void SolveDeadCode(SchemeFunction function)
{
//For each command C:
//. If C uses local variable X that is in V, as input, we remove X from V and the corresponding line from L
//. If C has local variable output X that is in V, then we remove the line of code that is connected to X (found in L)
//. If C has local variable output, we store the output variable's name in array V, and the code line in L
//. If we reach new basic block, we clear V and L
bool changed = true;
while (changed)
{
changed = false;
HashSet <int> blocks = GetBlockPositions(function);
var commands = function.Commands;
HashSet <int> removableIndexes = new HashSet <int>();
Dictionary <string, int> lastSetLines = new Dictionary <string, int>();
for (int i = 0; i < commands.Count; ++i)
{
if (blocks.Contains(i))
{
lastSetLines.Clear();
}
ISchemeCommand cmd = commands[i];
if (cmd is CommandCreateVariable)
{
continue; //We don't want to remove CREATE commands
}
List <string> inputs = cmd.GetInputs();
List <string> outputs = cmd.GetOutputs();
if (inputs != null)
{
foreach (string input in inputs)
{
if (SchemeExecutor.IsVariable(input))
{
lastSetLines.Remove(input);
}
}
}
if (outputs != null)
{
foreach (string output in outputs)
{
if (SchemeExecutor.IsVariable(output))
{
if (lastSetLines.ContainsKey(output))
{
removableIndexes.Add(lastSetLines[output]);
}
lastSetLines[output] = i;
}
}
}
}
if (removableIndexes.Count > 0)
{
changed = true;
RemoveCommandsAt(function, removableIndexes);
}
}
}
public static void SolveRegisterBuffers(SchemeFunction function)
{
// if an operation stores its result in a register <reg>, and it is followed by a SET(<var>, <reg>) command
// we delete the SET command and set the opperation's output to <var>
// we iterate over the following commands and change any <reg> to <var>
// we stop if <reg> is set again or we leave the block
var commands = function.Commands;
HashSet <int> removableIndexes = new HashSet <int>();
for (int i = 0; i < commands.Count; ++i)
{
ISchemeCommand cmd = commands[i];
var outputs = cmd.GetOutputs();
if (outputs == null)
{
continue;
}
// check if any output is a register
foreach (var reg in outputs)
{
if (SchemeExecutor.IsRegister(reg))
{
string variable = null;
for (int j = i + 1; j < commands.Count; ++j)
{
ISchemeCommand cmd2 = commands[j];
if (cmd2 is CommandJumpBase)
{
break; // break if we leave the block
}
if (cmd2.HasOutput(reg))
{
break; // break if the register is set again
}
if (cmd2 is CommandSetVariable && cmd2.HasInput(reg))
{
CommandSetVariable setCmd = (CommandSetVariable)cmd2;
variable = setCmd.GetVariableName();
if (SchemeExecutor.IsRegister(variable))
{
variable = null;
}
else
{
cmd.ChangeOutput(reg, variable);
removableIndexes.Add(j);
}
}
if (variable != null && cmd2.HasInput(reg))
{
cmd2.ChangeInputs(reg, variable);
}
}
}
}
}
RemoveCommandsAt(function, removableIndexes);
}