+/// determineREX - Determine if the MachineInstr has to be encoded with a X86-64
+/// REX prefix which specifies 1) 64-bit instructions, 2) non-default operand
+/// size, and 3) use of X86-64 extended registers.
+static unsigned determineREX(const MachineInstr &MI) {
+ unsigned REX = 0;
+ const MCInstrDesc &Desc = MI.getDesc();
+
+ // Pseudo instructions do not need REX prefix byte.
+ if ((Desc.TSFlags & X86II::FormMask) == X86II::Pseudo)
+ return 0;
+ if (Desc.TSFlags & X86II::REX_W)
+ REX |= 1 << 3;
+
+ unsigned NumOps = Desc.getNumOperands();
+ if (NumOps) {
+ bool isTwoAddr = NumOps > 1 &&
+ Desc.getOperandConstraint(1, MCOI::TIED_TO) != -1;
+
+ // If it accesses SPL, BPL, SIL, or DIL, then it requires a 0x40 REX prefix.
+ unsigned i = isTwoAddr ? 1 : 0;
+ for (unsigned e = NumOps; i != e; ++i) {
+ const MachineOperand& MO = MI.getOperand(i);
+ if (MO.isReg()) {
+ unsigned Reg = MO.getReg();
+ if (X86II::isX86_64NonExtLowByteReg(Reg))
+ REX |= 0x40;
+ }
+ }
+
+ switch (Desc.TSFlags & X86II::FormMask) {
+ case X86II::MRMInitReg:
+ if (X86InstrInfo::isX86_64ExtendedReg(MI.getOperand(0)))
+ REX |= (1 << 0) | (1 << 2);
+ break;
+ case X86II::MRMSrcReg: {
+ if (X86InstrInfo::isX86_64ExtendedReg(MI.getOperand(0)))
+ REX |= 1 << 2;
+ i = isTwoAddr ? 2 : 1;
+ for (unsigned e = NumOps; i != e; ++i) {
+ const MachineOperand& MO = MI.getOperand(i);
+ if (X86InstrInfo::isX86_64ExtendedReg(MO))
+ REX |= 1 << 0;
+ }
+ break;
+ }
+ case X86II::MRMSrcMem: {
+ if (X86InstrInfo::isX86_64ExtendedReg(MI.getOperand(0)))
+ REX |= 1 << 2;
+ unsigned Bit = 0;
+ i = isTwoAddr ? 2 : 1;
+ for (; i != NumOps; ++i) {
+ const MachineOperand& MO = MI.getOperand(i);
+ if (MO.isReg()) {
+ if (X86InstrInfo::isX86_64ExtendedReg(MO))
+ REX |= 1 << Bit;
+ Bit++;
+ }
+ }
+ break;
+ }
+ case X86II::MRM0m: case X86II::MRM1m:
+ case X86II::MRM2m: case X86II::MRM3m:
+ case X86II::MRM4m: case X86II::MRM5m:
+ case X86II::MRM6m: case X86II::MRM7m:
+ case X86II::MRMDestMem: {
+ unsigned e = (isTwoAddr ? X86::AddrNumOperands+1 : X86::AddrNumOperands);
+ i = isTwoAddr ? 1 : 0;
+ if (NumOps > e && X86InstrInfo::isX86_64ExtendedReg(MI.getOperand(e)))
+ REX |= 1 << 2;
+ unsigned Bit = 0;
+ for (; i != e; ++i) {
+ const MachineOperand& MO = MI.getOperand(i);
+ if (MO.isReg()) {
+ if (X86InstrInfo::isX86_64ExtendedReg(MO))
+ REX |= 1 << Bit;
+ Bit++;
+ }
+ }
+ break;
+ }
+ default: {
+ if (X86InstrInfo::isX86_64ExtendedReg(MI.getOperand(0)))
+ REX |= 1 << 0;
+ i = isTwoAddr ? 2 : 1;
+ for (unsigned e = NumOps; i != e; ++i) {
+ const MachineOperand& MO = MI.getOperand(i);
+ if (X86InstrInfo::isX86_64ExtendedReg(MO))
+ REX |= 1 << 2;
+ }
+ break;
+ }
+ }
+ }
+ return REX;
+}
+
+