+/// \brief If a movsx instruction has a shorter encoding for the used register
+/// simplify the instruction to use it instead.
+static void SimplifyMOVSX(MCInst &Inst) {
+ unsigned NewOpcode = 0;
+ unsigned Op0 = Inst.getOperand(0).getReg(), Op1 = Inst.getOperand(1).getReg();
+ switch (Inst.getOpcode()) {
+ default:
+ llvm_unreachable("Unexpected instruction!");
+ case X86::MOVSX16rr8: // movsbw %al, %ax --> cbtw
+ if (Op0 == X86::AX && Op1 == X86::AL)
+ NewOpcode = X86::CBW;
+ break;
+ case X86::MOVSX32rr16: // movswl %ax, %eax --> cwtl
+ if (Op0 == X86::EAX && Op1 == X86::AX)
+ NewOpcode = X86::CWDE;
+ break;
+ case X86::MOVSX64rr32: // movslq %eax, %rax --> cltq
+ if (Op0 == X86::RAX && Op1 == X86::EAX)
+ NewOpcode = X86::CDQE;
+ break;
+ }
+
+ if (NewOpcode != 0) {
+ Inst = MCInst();
+ Inst.setOpcode(NewOpcode);
+ }
+}
+