Fix a warning about an unreachable default in a switch statement.

[mehdi_amini]

mlir/lib/Dialect/StandardOps/IR/Ops.cpp

625

(like here)

699

I have vague memory that another compiler would warn if the function does not return after the switch if you remove this. I see other cases in the codebase where we don't provide the default (I assume to not hit the fully covered warning you hit) but the unreachable is still present after the switch.

[lattner]

Avoid warning for other compilers.

mlir/lib/Dialect/StandardOps/IR/Ops.cpp

case CmpIPredicate::ult:
     return lhs.ult(rhs);
   case CmpIPredicate::ule:
     return lhs.ule(rhs);
   case CmpIPredicate::ugt:
     return lhs.ugt(rhs);
   case CmpIPredicate::uge:
     return lhs.uge(rhs);
   }
   llvm_unreachable("unknown comparison predicate");
 }
 
 // Constant folding hook for comparisons.
 OpFoldResult CmpIOp::fold(ArrayRef<Attribute> operands) {
   assert(operands.size() == 2 && "cmpi takes two arguments");
 
   auto lhs = operands.front().dyn_cast_or_null<IntegerAttr>();
   auto rhs = operands.back().dyn_cast_or_null<IntegerAttr>();
case CmpFPredicate::ULE:
     return cmpResult == APFloat::cmpUnordered ||
            cmpResult == APFloat::cmpLessThan || cmpResult == APFloat::cmpEqual;
   case CmpFPredicate::UNE:
     return cmpResult != APFloat::cmpEqual;
   case CmpFPredicate::UNO:
     return cmpResult == APFloat::cmpUnordered;
   case CmpFPredicate::AlwaysTrue:
     return true;
-  default:
-    llvm_unreachable("unknown comparison predicate");
   }
 }
 
 // Constant folding hook for comparisons.
 OpFoldResult CmpFOp::fold(ArrayRef<Attribute> operands) {
   assert(operands.size() == 2 && "cmpf takes two arguments");
 
   auto lhs = operands.front().dyn_cast_or_null<FloatAttr>();