[llvm] TargetInstrInfo: make getOperandLatency return optional (NFC) (PR #73769)

[Björn Pettersson via llvm-commits]

================
@@ -1452,8 +1452,9 @@ bool TargetInstrInfo::hasLowDefLatency(const TargetSchedModel &SchedModel,
     return false;
 
   unsigned DefClass = DefMI.getDesc().getSchedClass();
-  int DefCycle = ItinData->getOperandCycle(DefClass, DefIdx);
-  return (DefCycle != -1 && DefCycle <= 1);
+  std::optional<unsigned> DefCycle =
+      ItinData->getOperandCycle(DefClass, DefIdx);
+  return DefCycle <= 1;
----------------
bjope wrote:

In the past `DefCycle == -1` resulted in `false`. Now `DefCycle <= 1` is the same as `DefCycle ? *DefCycle : true` so that will return true when getOperandCycle didn't return a proper value.

This at least impacts MachineLICM (when checking `IsCheapInstruction`).

https://github.com/llvm/llvm-project/pull/73769