// If we can emit optimized code for the cycle in moves starting at position i,
// do so, and return true.
bool
MoveEmitterX86::maybeEmitOptimizedCycle(const MoveResolver& moves, size_t i,
bool allGeneralRegs, bool allFloatRegs, size_t swapCount)
{
if (allGeneralRegs && swapCount <= 2) {
// Use x86's swap-integer-registers instruction if we only have a few
// swaps. (x86 also has a swap between registers and memory but it's
// slow.)
for (size_t k = 0; k < swapCount; k++)
masm.xchg(moves.getMove(i + k).to().reg(), moves.getMove(i + k + 1).to().reg());
return true;
}
if (allFloatRegs && swapCount == 1) {
// There's no xchg for xmm registers, but if we only need a single swap,
// it's cheap to do an XOR swap.
FloatRegister a = moves.getMove(i).to().floatReg();
FloatRegister b = moves.getMove(i + 1).to().floatReg();
masm.vxorpd(a, b, b);
masm.vxorpd(b, a, a);
masm.vxorpd(a, b, b);
return true;
}
return false;
}
// Examine the cycle in moves starting at position i. Determine if it's a
// simple cycle consisting of all register-to-register moves in a single class,
// and whether it can be implemented entirely by swaps.
size_t
MoveEmitterX86::characterizeCycle(const MoveResolver &moves, size_t i,
bool *allGeneralRegs, bool *allFloatRegs)
{
size_t swapCount = 0;
for (size_t j = i; ; j++) {
const Move &move = moves.getMove(j);
// If it isn't a cycle of registers of the same kind, we won't be able
// to optimize it.
if (!move.to().isGeneralReg())
*allGeneralRegs = false;
if (!move.to().isFloatReg())
*allFloatRegs = false;
if (!*allGeneralRegs && !*allFloatRegs)
return -1;
// The first and last move of the cycle are marked with inCycle(). Stop
// iterating when we see the last one.
if (j != i && move.inCycle())
break;
// Check that this move is actually part of the cycle. This is
// over-conservative when there are multiple reads from the same source,
// but that's expected to be rare.
if (move.from() != moves.getMove(j + 1).to()) {
*allGeneralRegs = false;
*allFloatRegs = false;
return -1;
}
swapCount++;
}
// Check that the last move cycles back to the first move.
const Move &move = moves.getMove(i + swapCount);
if (move.from() != moves.getMove(i).to()) {
*allGeneralRegs = false;
*allFloatRegs = false;
return -1;
}
return swapCount;
}
void MoveEmitterARM64::emit(const MoveResolver& moves) {
if (moves.numCycles()) {
masm.reserveStack(sizeof(void*));
pushedAtCycle_ = masm.framePushed();
}
for (size_t i = 0; i < moves.numMoves(); i++) {
emitMove(moves.getMove(i));
}
}
void
MoveEmitterMIPS::emit(const MoveResolver &moves)
{
if (moves.hasCycles()) {
// Reserve stack for cycle resolution
masm.reserveStack(sizeof(double));
pushedAtCycle_ = masm.framePushed();
}
for (size_t i = 0; i < moves.numMoves(); i++)
emit(moves.getMove(i));
}
void
MoveEmitterX86::emit(const MoveResolver &moves)
{
for (size_t i = 0; i < moves.numMoves(); i++) {
const MoveOp &move = moves.getMove(i);
const MoveOperand &from = move.from();
const MoveOperand &to = move.to();
if (move.isCycleEnd()) {
JS_ASSERT(inCycle_);
completeCycle(to, move.type());
inCycle_ = false;
continue;
}
if (move.isCycleBegin()) {
JS_ASSERT(!inCycle_);
// Characterize the cycle.
bool allGeneralRegs = true, allFloatRegs = true;
size_t swapCount = characterizeCycle(moves, i, &allGeneralRegs, &allFloatRegs);
// Attempt to optimize it to avoid using the stack.
if (maybeEmitOptimizedCycle(moves, i, allGeneralRegs, allFloatRegs, swapCount)) {
i += swapCount;
continue;
}
// Otherwise use the stack.
breakCycle(to, move.endCycleType());
inCycle_ = true;
}
// A normal move which is not part of a cycle.
switch (move.type()) {
case MoveOp::FLOAT32:
emitFloat32Move(from, to);
break;
case MoveOp::DOUBLE:
emitDoubleMove(from, to);
break;
case MoveOp::INT32:
emitInt32Move(from, to);
break;
case MoveOp::GENERAL:
emitGeneralMove(from, to);
break;
default:
MOZ_ASSUME_UNREACHABLE("Unexpected move type");
}
}
}
void
MoveEmitterX86::emit(const MoveResolver &moves)
{
for (size_t i = 0; i < moves.numMoves(); i++) {
const Move &move = moves.getMove(i);
const MoveOperand &from = move.from();
const MoveOperand &to = move.to();
if (move.inCycle()) {
// If this is the end of a cycle for which we're using the stack,
// handle the end.
if (inCycle_) {
completeCycle(to, move.kind());
inCycle_ = false;
continue;
}
// Characterize the cycle.
bool allGeneralRegs = true, allFloatRegs = true;
size_t swapCount = characterizeCycle(moves, i, &allGeneralRegs, &allFloatRegs);
// Attempt to optimize it to avoid using the stack.
if (maybeEmitOptimizedCycle(moves, i, allGeneralRegs, allFloatRegs, swapCount)) {
i += swapCount;
continue;
}
// Otherwise use the stack.
breakCycle(to, move.kind());
inCycle_ = true;
}
// A normal move which is not part of a cycle.
if (move.kind() == Move::DOUBLE)
emitDoubleMove(from, to);
else
emitGeneralMove(from, to);
}
}
void
MoveEmitterX86::emit(const MoveResolver& moves)
{
#if defined(JS_CODEGEN_X86) && defined(DEBUG)
// Clobber any scratch register we have, to make regalloc bugs more visible.
if (hasScratchRegister())
masm.mov(ImmWord(0xdeadbeef), scratchRegister());
#endif
for (size_t i = 0; i < moves.numMoves(); i++) {
const MoveOp& move = moves.getMove(i);
const MoveOperand& from = move.from();
const MoveOperand& to = move.to();
if (move.isCycleEnd()) {
MOZ_ASSERT(inCycle_);
completeCycle(to, move.type());
inCycle_ = false;
continue;
}
if (move.isCycleBegin()) {
MOZ_ASSERT(!inCycle_);
// Characterize the cycle.
bool allGeneralRegs = true, allFloatRegs = true;
size_t swapCount = characterizeCycle(moves, i, &allGeneralRegs, &allFloatRegs);
// Attempt to optimize it to avoid using the stack.
if (maybeEmitOptimizedCycle(moves, i, allGeneralRegs, allFloatRegs, swapCount)) {
i += swapCount;
continue;
}
// Otherwise use the stack.
breakCycle(to, move.endCycleType());
inCycle_ = true;
}
// A normal move which is not part of a cycle.
switch (move.type()) {
case MoveOp::FLOAT32:
emitFloat32Move(from, to);
break;
case MoveOp::DOUBLE:
emitDoubleMove(from, to);
break;
case MoveOp::INT32:
emitInt32Move(from, to);
break;
case MoveOp::GENERAL:
emitGeneralMove(from, to);
break;
case MoveOp::INT32X4:
emitInt32X4Move(from, to);
break;
case MoveOp::FLOAT32X4:
emitFloat32X4Move(from, to);
break;
default:
MOZ_CRASH("Unexpected move type");
}
}
}