/**
* Attempt to generate a boolean compare opcode from a conditional branch.
*
* <pre>
* 1) IF .. GOTO A replaced by BOOLEAN_CMP x=..
* x = 0
* GOTO B
* A: x = 1
* B: ...
* </pre>
*
* <p>Precondition: <code>IfCmp.conforms(<i>cb</i>)</code>
*
* @param ir governing IR
* @param bb basic block of cb
* @param cb conditional branch instruction
* @return true if the transformation succeeds, false otherwise
*/
private boolean generateBooleanCompare(IR ir, BasicBlock bb, Instruction cb, BasicBlock tb) {
if ((cb.operator() != INT_IFCMP) && (cb.operator() != REF_IFCMP)) {
return false;
}
// make sure this is the last branch in the block
if (cb.nextInstructionInCodeOrder().operator() != BBEND) {
return false;
}
Operand val1 = IfCmp.getVal1(cb);
Operand val2 = IfCmp.getVal2(cb);
ConditionOperand condition = IfCmp.getCond(cb);
// "not taken" path
BasicBlock fb = cb.getBasicBlock().getNotTakenNextBlock();
// make sure it's a diamond
if (tb.getNumberOfNormalOut() != 1) {
return false;
}
if (fb.getNumberOfNormalOut() != 1) {
return false;
}
BasicBlock jb = fb.getNormalOut().nextElement(); // join block
// make sure it's a diamond
if (!tb.pointsOut(jb)) {
return false;
}
Instruction ti = tb.firstRealInstruction();
Instruction fi = fb.firstRealInstruction();
// make sure the instructions in target blocks are either both moves
// or both returns
if (ti == null || fi == null) {
return false;
}
if (ti.operator() != fi.operator()) {
return false;
}
if (ti.operator != RETURN && ti.operator() != INT_MOVE) {
return false;
}
//
// WARNING: This code is currently NOT exercised!
//
if (ti.operator() == RETURN) {
// make sure each of the target blocks contains only one instruction
if (ti != tb.lastRealInstruction()) {
return false;
}
if (fi != fb.lastRealInstruction()) {
return false;
}
Operand tr = Return.getVal(ti);
Operand fr = Return.getVal(fi);
// make sure we're returning constants
if (!(tr instanceof IntConstantOperand) || !(fr instanceof IntConstantOperand)) {
return false;
}
int tv = ((IntConstantOperand) tr).value;
int fv = ((IntConstantOperand) fr).value;
if (!((tv == 1 && fv == 0) || (tv == 1 && fv == 0))) {
return false;
}
RegisterOperand t = ir.regpool.makeTemp(TypeReference.Boolean);
// Cases 1) and 2)
if (tv == 0) {
condition = condition.flipCode();
}
booleanCompareHelper(cb, t, val1.copy(), val2.copy(), condition);
cb.insertAfter(Return.create(RETURN, t.copyD2U()));
} else { // (ti.operator() == INT_MOVE)
// make sure each of the target blocks only does the move
if (ti != tb.lastRealInstruction() && ti.nextInstructionInCodeOrder().operator() != GOTO) {
return false;
}
if (fi != fb.lastRealInstruction() && fi.nextInstructionInCodeOrder().operator() != GOTO) {
return false;
}
RegisterOperand t = Move.getResult(ti);
// make sure both moves are to the same register
if (t.getRegister() != Move.getResult(fi).getRegister()) {
return false;
}
Operand tr = Move.getVal(ti);
Operand fr = Move.getVal(fi);
// make sure we're assigning constants
if (!(tr instanceof IntConstantOperand) || !(fr instanceof IntConstantOperand)) {
return false;
}
int tv = ((IntConstantOperand) tr).value;
int fv = ((IntConstantOperand) fr).value;
if (!((tv == 1 && fv == 0) || (tv == 0 && fv == 1))) {
return false;
}
// Cases 3) and 4)
if (tv == 0) {
condition = condition.flipCode();
}
booleanCompareHelper(cb, t.copyRO(), val1.copy(), val2.copy(), condition);
Instruction next = cb.nextInstructionInCodeOrder();
if (next.operator() == GOTO) {
Goto.setTarget(next, jb.makeJumpTarget());
} else {
cb.insertAfter(jb.makeGOTO());
}
}
// fixup CFG
bb.deleteOut(tb);
bb.deleteOut(fb);
bb.insertOut(jb); // Note: if we processed returns,
// jb is the exit node.
return true;
}
/**
* 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
}
