public boolean optimizeRegisterAllocation(RegAllocContext context, int nMaxRegisters) {
boolean bChanges = false;
ArrayList<Instruction> removeList = new ArrayList<Instruction>();
// Iterate through instructions
for (int i = 0; i < getLines().getNumItems(); i++) {
Line line = getLines().getItemAtIndex(i);
Instruction nextInstr = getNextInstr(getLines(), i);
if (Line.Type.INSTRUCTION == line.getType()) {
Instruction instr = (Instruction) line;
// If this is a LI instruction
if (0 == instr.getInstruction().compareTo("li")) {
// If the register is $v0, do nothing
if (0 != instr.getArgument1().getName().compareTo("$v0")) {
// Allocate Free register for dest
String strFreeReg = findFirstFreeReg(context, instr.getLiveSet(), nMaxRegisters);
// Map old register to this instruction
context.mapRegToInstruction.put(instr.getArgument1().getName(), instr);
context.regMap.put(strFreeReg, instr.getArgument2().getName());
context.variableLocs.put(instr.getArgument2().getName(), strFreeReg);
// Rewrite Argument1 with new register
instr.getArgument1().setOrigName(strFreeReg);
}
}
// If this is a LW instruction
else if (0 == instr.getInstruction().compareTo("lw")) {
// If the variable is in a register, then remove this instruction
if (0 != context.variableLocs.get(instr.getArgument2().getName()).compareTo("m")) {
Line nextLine = getLines().getItemAtIndex(i + 1);
Instruction next = null;
if (Line.Type.INSTRUCTION == nextLine.getType()) next = (Instruction) nextLine;
if (null == next || 0 != next.getInstruction().compareTo("sw")) removeList.add(instr);
}
// else if the variable is live,
else // if(instr.getLiveSet().contains(instr.getArgument2().getName()))
{
// 1) allocate free register
String strFreeReg = findFirstFreeReg(context, instr.getLiveSet(), nMaxRegisters);
// 2) patch instruction
if (null != strFreeReg) {
context.regMap.put(strFreeReg, instr.getArgument2().getName());
context.variableLocs.put(instr.getArgument2().getName(), strFreeReg);
instr.getArgument1().setOrigName(strFreeReg);
}
}
}
// If this is a SW instruction
else if (0 == instr.getInstruction().compareTo("sw")) {
// If the register is $v0, do nothing
if (0 != instr.getArgument1().getName().compareTo("$v0")) {
// If the instruction that is mapped to the register is an LW, then use the register
// from that instruction.
Line prevLine = getLines().getItemAtIndex(i - 1);
Instruction prevInstr = null;
if (Line.Type.INSTRUCTION == prevLine.getType()) prevInstr = (Instruction) prevLine;
// context.mapRegToInstruction.get(instr.getArgument1().getOrigName());
if (null != prevInstr && 0 == prevInstr.getInstruction().compareTo("lw")) {
String strReg = prevInstr.getArgument1().getOrigName();
instr.getArgument1().setOrigName(strReg);
context.regMap.put(strReg, instr.getArgument2().getName());
context.variableLocs.put(instr.getArgument2().getName(), strReg);
}
// If the variable is live
else if (null != nextInstr
&& nextInstr.getLiveSet().contains(instr.getArgument2().getName())) {
// Add the variable to the live set
instr.getLiveSet().add(instr.getArgument2().getName());
String strOldReg = instr.getArgument1().getOrigName();
String strNewReg = "";
// If the variable is already in a register
if (0 != context.variableLocs.get(instr.getArgument2().getName()).compareTo("m")) {
// Patch current instruction to use that register
strNewReg = context.variableLocs.get(instr.getArgument2().getName());
instr.getArgument1().setOrigName(strNewReg);
}
// Else
else {
// Allocate free register
strNewReg = findFirstFreeReg(context, instr.getLiveSet(), nMaxRegisters);
// patch instruction
if (null != strNewReg) {
context.regMap.put(strNewReg, instr.getArgument2().getName());
context.variableLocs.put(instr.getArgument2().getName(), strNewReg);
instr.getArgument1().setOrigName(strNewReg);
}
}
// Patch register's last-used instruction
Instruction oldInstr = context.mapRegToInstruction.get(strOldReg);
if (null != oldInstr) oldInstr.getArgument1().setOrigName(strNewReg);
}
// If the previous instruction is an operation...
else if (null != prevInstr && prevInstr.isOperation()) {
String strReg = prevInstr.getArgument1().getOrigName();
instr.getArgument1().setOrigName(strReg);
// Remove the mapping from the register to the instruction
context.mapRegToInstruction.remove(prevInstr.getArgument1().getName());
// context.regMap.put(strReg, instr.getArgument2().getName());
// context.variableLocs.put(instr.getArgument2().getName(), strReg);
}
// If the register is mapped to a variable held in a register
else if (instr.getMapRegToValue().containsKey(instr.getArgument1().getName())) {
String strOldReg = instr.getArgument1().getName();
String strVar = instr.getMapRegToValue().get(instr.getArgument1().getName());
String strNewReg = context.variableLocs.get(strVar);
if (null != strNewReg && 0 != strNewReg.compareTo("m")) {
// Update the register
instr.getArgument1().setOrigName(strNewReg);
// Find last instruction that referenced old reg
Instruction oldInstr = context.mapRegToInstruction.get(strOldReg);
if (null != oldInstr) {
oldInstr.getArgument1().setOrigName(strNewReg);
}
}
} else
// Use temp
{
String strOldReg = instr.getArgument1().getName();
// Allocate temp register for dest
String strTempReg = getTempRegister(nMaxRegisters);
// Update the register
instr.getArgument1().setOrigName(strTempReg);
// Find last instruction that referenced old reg
Instruction oldInstr = context.mapRegToInstruction.get(strOldReg);
if (null != oldInstr) {
oldInstr.getArgument1().setOrigName(strTempReg);
}
}
}
}
// If it is the NEG function
else if (0 == instr.getInstruction().compareTo("neg")) {
remapRegister(context, instr, instr.getArgument1());
}
// If this is another non-jump instruction
else if (!instr.getIsJump()
&& 0 != instr.getInstruction().compareTo("syscall")
&& 0 != instr.getInstruction().compareTo("move")) {
// Allocate temp register for dest
String strTempReg = getTempRegister(nMaxRegisters);
// Map old register to this instruction
context.mapRegToInstruction.put(instr.getArgument1().getName(), instr);
// Rewrite Argument1 with temp register
instr.getArgument1().setOrigName(strTempReg);
remapRegister(context, instr, instr.getArgument2());
remapRegister(context, instr, instr.getArgument3());
} else if (0 == instr.getInstruction().compareTo("move")) {
remapRegister(context, instr, instr.getArgument2());
}
// If this is a jump instruction
else if (instr.getIsJump() && Instruction.BranchType.JUMP != instr.getBranchType()) {
String strTempReg = getTempRegister(nMaxRegisters);
// Rewrite Argument1 with temp register
instr.getArgument1().setOrigName(strTempReg);
}
}
deallocateNonLiveVars(line, context, nMaxRegisters);
}
// Remove lines
for (int i = 0; i < removeList.size(); i++) {
getLines().removeLine(removeList.get(i));
}
return bChanges;
}
