[AArch64] xor -1 can be mvn, so make it free

Author: AZero13

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -443,6 +443,10 @@ InstructionCost AArch64TTIImpl::getIntImmCostInst(unsigned Opcode, unsigned Idx,
   case Instruction::Store:
     ImmIdx = 0;
     break;
+  case Instruction::Xor:
+    if (Idx == 1 && (BitSize == 32 || BitSize == 64) && Imm.isAllOnes())
+      return TTI::TCC_Free; // xor a, -1 can be folded to MVN
+  [[fallthrough]];
   case Instruction::Add:
   case Instruction::Sub:
   case Instruction::Mul:
@@ -452,7 +456,6 @@ InstructionCost AArch64TTIImpl::getIntImmCostInst(unsigned Opcode, unsigned Idx,
   case Instruction::SRem:
   case Instruction::And:
   case Instruction::Or:
-  case Instruction::Xor:
   case Instruction::ICmp:
     ImmIdx = 1;
     break;