DAG: Fix naming crime

[arsenm]

Summary

Because isOperationCustom was only checking for custom
lowering on illegal types, this was behaving inconsistently
with the other isOperation* functions, so that
isOperationLegalOrCustom != (isOperationLegal || isOperationCustom)

Luckily this is only used in one place which already checks the
type legality on its own.

[arsenm]

r311743

include/llvm/Target/TargetLowering.h

public:
   /// guide high-level lowering decisions.
   bool isOperationLegalOrCustomOrPromote(unsigned Op, EVT VT) const {
     return (VT == MVT::Other || isTypeLegal(VT)) &&
       (getOperationAction(Op, VT) == Legal ||
        getOperationAction(Op, VT) == Custom ||
        getOperationAction(Op, VT) == Promote);
   }
 
-  /// Return true if the specified operation is illegal but has a custom lowering
-  /// on that type. This is used to help guide high-level lowering
-  /// decisions.
+  /// Return true if the operation uses custom lowering, regardless of whether
+  /// the type is legal or not.
   bool isOperationCustom(unsigned Op, EVT VT) const {
-    return (!isTypeLegal(VT) && getOperationAction(Op, VT) == Custom);
+    return getOperationAction(Op, VT) == Custom;
   }
 
   /// Return true if lowering to a jump table is allowed.
   bool areJTsAllowed(const Function *Fn) const {
     if (Fn->getFnAttribute("no-jump-tables").getValueAsString() == "true")
       return false;
 
     return isOperationLegalOrCustom(ISD::BR_JT, MVT::Other) ||