[mlir] Make OpResult usable with DenseSet etc.

[springerm]

Summary

DenseSet<Value> works but DenseSet<OpResult> currently results in a compile error.

[springerm]

fix typo

mlir/include/mlir/IR/Value.h

static mlir::BlockArgument getEmptyKey() {
     void *pointer = llvm::DenseMapInfo<void *>::getEmptyKey();
     return reinterpret_cast<mlir::detail::BlockArgumentImpl *>(pointer);
   }
   static mlir::BlockArgument getTombstoneKey() {
     void *pointer = llvm::DenseMapInfo<void *>::getTombstoneKey();
     return reinterpret_cast<mlir::detail::BlockArgumentImpl *>(pointer);
   }
 };
+template <>
+struct DenseMapInfo<mlir::OpResult> : public DenseMapInfo<mlir::Value> {
+  static mlir::OpResult getEmptyKey() {
+    void *pointer = llvm::DenseMapInfo<void *>::getEmptyKey();
+    return reinterpret_cast<mlir::detail::OpResultImpl *>(pointer);
+  }
+  static mlir::OpResult getTombstoneKey() {
+    void *pointer = llvm::DenseMapInfo<void *>::getTombstoneKey();
+    return reinterpret_cast<mlir::detail::OpResultImpl *>(pointer);
+  }
+};
 
 /// Allow stealing the low bits of a value.
 template <>
 struct PointerLikeTypeTraits<mlir::Value> {
 public:
   static inline void *getAsVoidPointer(mlir::Value value) {
     return const_cast<void *>(value.getAsOpaquePointer());
   }
   static inline mlir::Value getFromVoidPointer(void *pointer) {
     return mlir::Value::getFromOpaquePointer(pointer);
   }
   enum {
     NumLowBitsAvailable =
         PointerLikeTypeTraits<mlir::detail::ValueImpl *>::NumLowBitsAvailable
   };
 };
 template <>
 struct PointerLikeTypeTraits<mlir::BlockArgument>
     : public PointerLikeTypeTraits<mlir::Value> {
 public:
   static inline mlir::BlockArgument getFromVoidPointer(void *pointer) {
     return reinterpret_cast<mlir::detail::BlockArgumentImpl *>(pointer);
   }
 };
+template <>
+struct PointerLikeTypeTraits<mlir::OpResult>
+    : public PointerLikeTypeTraits<mlir::Value> {
+public:
+  static inline mlir::OpResult getFromVoidPointer(void *pointer) {
+    return reinterpret_cast<mlir::detail::OpResultImpl *>(pointer);
+  }
+};
 
 } // end namespace llvm
 
 #endif