/** Evaluate the cost of a basic block, in number of real instructions. */
private int evaluateCost(BasicBlock bb) {
int result = 0;
for (Enumeration<Instruction> e = bb.forwardRealInstrEnumerator(); e.hasMoreElements(); ) {
Instruction s = e.nextElement();
if (!s.isBranch()) result++;
}
return result;
}
/**
* For each real non-branch instruction s in bb,
*
* <ul>
* <li>Copy s to s', and store s' in the returned array
* <li>Insert the function s->s' in the map
* </ul>
*/
private Instruction[] copyAndMapInstructions(
BasicBlock bb, HashMap<Instruction, Instruction> map) {
if (bb == null) return new Instruction[0];
int count = 0;
// first count the number of instructions
for (Enumeration<Instruction> e = bb.forwardRealInstrEnumerator(); e.hasMoreElements(); ) {
Instruction s = e.nextElement();
if (s.isBranch()) continue;
count++;
}
// now copy.
Instruction[] result = new Instruction[count];
int i = 0;
for (Enumeration<Instruction> e = bb.forwardRealInstrEnumerator(); e.hasMoreElements(); ) {
Instruction s = e.nextElement();
if (s.isBranch()) continue;
Instruction sprime = s.copyWithoutLinks();
result[i++] = sprime;
map.put(s, sprime);
}
return result;
}
/**
* Walks through the IR. For each StackLocationOperand, replace the operand with the appropriate
* MemoryOperand.
*/
private void rewriteStackLocations() {
// ESP is initially WORDSIZE above where the framepointer is going to be.
ESPOffset = getFrameFixedSize() + WORDSIZE;
Register ESP = ((PhysicalRegisterSet) ir.regpool.getPhysicalRegisterSet()).getESP();
boolean seenReturn = false;
for (Enumeration<Instruction> e = ir.forwardInstrEnumerator(); e.hasMoreElements(); ) {
Instruction s = e.nextElement();
if (s.isReturn()) {
seenReturn = true;
continue;
}
if (s.isBranch()) {
// restore ESP to home location at end of basic block.
moveESPBefore(s, 0);
continue;
}
if (s.operator() == BBEND) {
if (seenReturn) {
// at a return ESP will be at FrameFixedSize,
seenReturn = false;
ESPOffset = 0;
} else {
moveESPBefore(s, 0);
}
continue;
}
if (s.operator() == ADVISE_ESP) {
ESPOffset = MIR_UnaryNoRes.getVal(s).asIntConstant().value;
continue;
}
if (s.operator() == REQUIRE_ESP) {
// ESP is required to be at the given offset from the bottom of the frame
moveESPBefore(s, MIR_UnaryNoRes.getVal(s).asIntConstant().value);
continue;
}
if (s.operator() == YIELDPOINT_PROLOGUE
|| s.operator() == YIELDPOINT_BACKEDGE
|| s.operator() == YIELDPOINT_EPILOGUE) {
moveESPBefore(s, 0);
continue;
}
if (s.operator() == IA32_MOV) {
rewriteMoveInstruction(s);
}
// pop computes the effective address of its operand after ESP
// is incremented. Therefore update ESPOffset before rewriting
// stacklocation and memory operands.
if (s.operator() == IA32_POP) {
ESPOffset += WORDSIZE;
}
for (Enumeration<Operand> ops = s.getOperands(); ops.hasMoreElements(); ) {
Operand op = ops.nextElement();
if (op instanceof StackLocationOperand) {
StackLocationOperand sop = (StackLocationOperand) op;
int offset = sop.getOffset();
if (sop.isFromTop()) {
offset = FPOffset2SPOffset(offset);
}
offset -= ESPOffset;
byte size = sop.getSize();
MemoryOperand M =
MemoryOperand.BD(
new RegisterOperand(ESP, PRIMITIVE_TYPE_FOR_WORD),
Offset.fromIntSignExtend(offset),
size,
null,
null);
s.replaceOperand(op, M);
} else if (op instanceof MemoryOperand) {
MemoryOperand M = op.asMemory();
if ((M.base != null && M.base.getRegister() == ESP)
|| (M.index != null && M.index.getRegister() == ESP)) {
M.disp = M.disp.minus(ESPOffset);
}
}
}
// push computes the effective address of its operand after ESP
// is decremented. Therefore update ESPOffset after rewriting
// stacklocation and memory operands.
if (s.operator() == IA32_PUSH) {
ESPOffset -= WORDSIZE;
}
}
}
/**
* Do any of the instructions in a basic block preclude eliminating the basic block with
* conditional moves?
*/
private boolean hasCMTaboo(BasicBlock bb) {
if (bb == null) return false;
// Note: it is taboo to assign more than once to any register in the
// block.
HashSet<Register> defined = new HashSet<Register>();
for (Enumeration<Instruction> e = bb.forwardRealInstrEnumerator(); e.hasMoreElements(); ) {
Instruction s = e.nextElement();
if (s.isBranch()) continue;
// for now, only the following opcodes are legal.
switch (s.operator.opcode) {
case INT_MOVE_opcode:
case REF_MOVE_opcode:
case DOUBLE_MOVE_opcode:
case FLOAT_MOVE_opcode:
case INT_ADD_opcode:
case REF_ADD_opcode:
case FLOAT_ADD_opcode:
case DOUBLE_ADD_opcode:
case INT_SUB_opcode:
case REF_SUB_opcode:
case FLOAT_SUB_opcode:
case DOUBLE_SUB_opcode:
case INT_MUL_opcode:
case FLOAT_MUL_opcode:
case DOUBLE_MUL_opcode:
case INT_NEG_opcode:
case FLOAT_NEG_opcode:
case DOUBLE_NEG_opcode:
case REF_SHL_opcode:
case INT_SHL_opcode:
case REF_SHR_opcode:
case INT_SHR_opcode:
case REF_USHR_opcode:
case INT_USHR_opcode:
case REF_AND_opcode:
case INT_AND_opcode:
case REF_OR_opcode:
case INT_OR_opcode:
case REF_XOR_opcode:
case INT_XOR_opcode:
case REF_NOT_opcode:
case INT_NOT_opcode:
case INT_2BYTE_opcode:
case INT_2USHORT_opcode:
case INT_2SHORT_opcode:
case FLOAT_2DOUBLE_opcode:
case DOUBLE_2FLOAT_opcode:
// these are OK.
break;
default:
return true;
}
// make sure no register is defined more than once in this block.
for (Enumeration<Operand> defs = s.getDefs(); defs.hasMoreElements(); ) {
Operand def = defs.nextElement();
if (VM.VerifyAssertions) VM._assert(def.isRegister());
Register r = def.asRegister().getRegister();
if (defined.contains(r)) return true;
defined.add(r);
}
}
return false;
}
/**
* Perform the transformation to replace conditional branch with a sequence using conditional
* moves.
*
* @param ir governing IR
* @param diamond the IR diamond structure to replace
* @param cb conditional branch instruction at the head of the diamond
*/
private void doCondMove(IR ir, Diamond diamond, Instruction cb) {
BasicBlock taken = diamond.getTaken();
BasicBlock notTaken = diamond.getNotTaken();
// for each non-branch instruction s in the diamond,
// copy s to a new instruction s'
// and store a mapping from s to s'
HashMap<Instruction, Instruction> takenInstructions = new HashMap<Instruction, Instruction>();
Instruction[] takenInstructionList = copyAndMapInstructions(taken, takenInstructions);
HashMap<Instruction, Instruction> notTakenInstructions =
new HashMap<Instruction, Instruction>();
Instruction[] notTakenInstructionList = copyAndMapInstructions(notTaken, notTakenInstructions);
// Extract the values and condition from the conditional branch.
Operand val1 = IfCmp.getVal1(cb);
Operand val2 = IfCmp.getVal2(cb);
ConditionOperand cond = IfCmp.getCond(cb);
// Copy val1 and val2 to temporaries, just in case they're defined in
// the diamond. If they're not defined in the diamond, copy prop
// should clean these moves up.
RegisterOperand tempVal1 = ir.regpool.makeTemp(val1);
Operator op = IRTools.getMoveOp(tempVal1.getType());
cb.insertBefore(Move.create(op, tempVal1.copyRO(), val1.copy()));
RegisterOperand tempVal2 = ir.regpool.makeTemp(val2);
op = IRTools.getMoveOp(tempVal2.getType());
cb.insertBefore(Move.create(op, tempVal2.copyRO(), val2.copy()));
// For each instruction in each temporary set, rewrite it to def a new
// temporary, and insert it before the branch.
rewriteWithTemporaries(takenInstructionList, ir);
rewriteWithTemporaries(notTakenInstructionList, ir);
insertBefore(takenInstructionList, cb);
insertBefore(notTakenInstructionList, cb);
// For each register defined in the TAKEN branch, save a mapping to
// the corresponding conditional move.
HashMap<Register, Instruction> takenMap = new HashMap<Register, Instruction>();
// Now insert conditional moves to replace each instruction in the diamond.
// First handle the taken branch.
if (taken != null) {
for (Enumeration<Instruction> e = taken.forwardRealInstrEnumerator(); e.hasMoreElements(); ) {
Instruction s = e.nextElement();
if (s.isBranch()) continue;
Operand def = s.getDefs().nextElement();
// if the register does not span a basic block, it is a temporary
// that will now be dead
if (def.asRegister().getRegister().spansBasicBlock()) {
Instruction tempS = takenInstructions.get(s);
RegisterOperand temp = (RegisterOperand) tempS.getDefs().nextElement();
op = IRTools.getCondMoveOp(def.asRegister().getType());
Instruction cmov =
CondMove.create(
op,
def.asRegister(),
tempVal1.copy(),
tempVal2.copy(),
cond.copy().asCondition(),
temp.copy(),
def.copy());
takenMap.put(def.asRegister().getRegister(), cmov);
cb.insertBefore(cmov);
}
s.remove();
}
}
// For each register defined in the NOT-TAKEN branch, save a mapping to
// the corresponding conditional move.
HashMap<Register, Instruction> notTakenMap = new HashMap<Register, Instruction>();
// Next handle the not taken branch.
if (notTaken != null) {
for (Enumeration<Instruction> e = notTaken.forwardRealInstrEnumerator();
e.hasMoreElements(); ) {
Instruction s = e.nextElement();
if (s.isBranch()) continue;
Operand def = s.getDefs().nextElement();
// if the register does not span a basic block, it is a temporary
// that will now be dead
if (def.asRegister().getRegister().spansBasicBlock()) {
Instruction tempS = notTakenInstructions.get(s);
RegisterOperand temp = (RegisterOperand) tempS.getDefs().nextElement();
Instruction prevCmov = takenMap.get(def.asRegister().getRegister());
if (prevCmov != null) {
// if this register was also defined in the taken branch, change
// the previous cmov with a different 'False' Value
CondMove.setFalseValue(prevCmov, temp.copy());
notTakenMap.put(def.asRegister().getRegister(), prevCmov);
} else {
// create a new cmov instruction
op = IRTools.getCondMoveOp(def.asRegister().getType());
Instruction cmov =
CondMove.create(
op,
def.asRegister(),
tempVal1.copy(),
tempVal2.copy(),
cond.copy().asCondition(),
def.copy(),
temp.copy());
cb.insertBefore(cmov);
notTakenMap.put(def.asRegister().getRegister(), cmov);
}
}
s.remove();
}
}
// Mutate the conditional branch into a GOTO.
BranchOperand target = diamond.getBottom().makeJumpTarget();
Goto.mutate(cb, GOTO, target);
// Delete a potential GOTO after cb.
Instruction next = cb.nextInstructionInCodeOrder();
if (next.operator != BBEND) {
next.remove();
}
// Recompute the CFG.
diamond.getTop().recomputeNormalOut(ir); // fix the CFG
}
