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

Author: AZero13

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -443,16 +443,18 @@ InstructionCost AArch64TTIImpl::getIntImmCostInst(unsigned Opcode, unsigned Idx,
   case Instruction::Store:
     ImmIdx = 0;
     break;
+  case Instruction::Xor:
+    if (Imm.isAllOnes())
+      return TTI::TCC_Free; // xor a, -1 can be folded to MVN
+  [[fallthrough]];
   case Instruction::Add:
   case Instruction::Sub:
   case Instruction::Mul:
   case Instruction::UDiv:
   case Instruction::SDiv:
   case Instruction::URem:
   case Instruction::SRem:
-  case Instruction::And:
   case Instruction::Or:
-  case Instruction::Xor:
   case Instruction::ICmp:
     ImmIdx = 1;
     break;
@@ -475,6 +477,11 @@ InstructionCost AArch64TTIImpl::getIntImmCostInst(unsigned Opcode, unsigned Idx,
   case Instruction::Ret:
   case Instruction::Load:
     break;
+  case Instruction::And:
+    if (Imm == 255 || Imm == 65535)
+      return TTI::TCC_Free;
+    ImmIdx = 1;
+    break;
   }
 
   if (Idx == ImmIdx) {