diff --git a/mlir/include/mlir/IR/AttrTypeBase.td b/mlir/include/mlir/IR/AttrTypeBase.td
--- a/mlir/include/mlir/IR/AttrTypeBase.td
+++ b/mlir/include/mlir/IR/AttrTypeBase.td
@@ -295,6 +295,8 @@
   // The C++ storage type of of this parameter if it is a reference, e.g.
   // `std::string` for `StringRef` or `SmallVector` for `ArrayRef`.
   string cppStorageType = ?;
+  // The C++ code to convert from the storage type to the parameter type.
+  string convertFromStorage = "$_self";
   // One-line human-readable description of the argument.
   string summary = desc;
   // The format string for the asm syntax (documentation only).
diff --git a/mlir/include/mlir/TableGen/AttrOrTypeDef.h b/mlir/include/mlir/TableGen/AttrOrTypeDef.h
--- a/mlir/include/mlir/TableGen/AttrOrTypeDef.h
+++ b/mlir/include/mlir/TableGen/AttrOrTypeDef.h
@@ -76,6 +76,9 @@
   /// Get the C++ storage type of this parameter.
   StringRef getCppStorageType() const;
 
+  /// Get the C++ code to convert from the storage type to the parameter type.
+  StringRef getConvertFromStorage() const;
+
   /// Get an optional C++ parameter parser.
   Optional<StringRef> getParser() const;
 
diff --git a/mlir/lib/TableGen/AttrOrTypeDef.cpp b/mlir/lib/TableGen/AttrOrTypeDef.cpp
--- a/mlir/lib/TableGen/AttrOrTypeDef.cpp
+++ b/mlir/lib/TableGen/AttrOrTypeDef.cpp
@@ -229,14 +229,9 @@
 }
 
 StringRef AttrOrTypeParameter::getCppType() const {
-  llvm::Init *parameterType = getDef();
-  if (auto *stringType = dyn_cast<llvm::StringInit>(parameterType))
+  if (auto *stringType = dyn_cast<llvm::StringInit>(getDef()))
     return stringType->getValue();
-  if (auto *param = dyn_cast<llvm::DefInit>(parameterType))
-    return param->getDef()->getValueAsString("cppType");
-  llvm::PrintFatalError(
-      "Parameters DAG arguments must be either strings or defs "
-      "which inherit from AttrOrTypeParameter\n");
+  return getDefValue<llvm::StringInit>("cppType").getValue();
 }
 
 StringRef AttrOrTypeParameter::getCppAccessorType() const {
@@ -248,6 +243,11 @@
   return getDefValue<llvm::StringInit>("cppStorageType").value_or(getCppType());
 }
 
+StringRef AttrOrTypeParameter::getConvertFromStorage() const {
+  return getDefValue<llvm::StringInit>("convertFromStorage")
+      .getValueOr("$_self");
+}
+
 Optional<StringRef> AttrOrTypeParameter::getParser() const {
   return getDefValue<llvm::StringInit>("parser");
 }
diff --git a/mlir/test/mlir-tblgen/attr-or-type-format.td b/mlir/test/mlir-tblgen/attr-or-type-format.td
--- a/mlir/test/mlir-tblgen/attr-or-type-format.td
+++ b/mlir/test/mlir-tblgen/attr-or-type-format.td
@@ -55,8 +55,8 @@
 // ATTR:   if (odsParser.parseRParen())
 // ATTR:     return {};
 // ATTR:   return TestAAttr::get(odsParser.getContext(),
-// ATTR:                         *_result_value,
-// ATTR:                         *_result_complex);
+// ATTR:                         (*_result_value),
+// ATTR:                         (*_result_complex));
 // ATTR: }
 
 // ATTR: void TestAAttr::print(::mlir::AsmPrinter &odsPrinter) const {
@@ -114,8 +114,8 @@
 // ATTR:       return {};
 // ATTR:   }
 // ATTR:   return TestBAttr::get(odsParser.getContext(),
-// ATTR:                         *_result_v0,
-// ATTR:                         *_result_v1);
+// ATTR:                         (*_result_v0),
+// ATTR:                         (*_result_v1));
 // ATTR: }
 
 // ATTR: void TestBAttr::print(::mlir::AsmPrinter &odsPrinter) const {
@@ -151,8 +151,8 @@
 // ATTR:   if (::mlir::failed(_result_v1))
 // ATTR:     return {};
 // ATTR:   return TestFAttr::get(odsParser.getContext(),
-// ATTR:     *_result_v0,
-// ATTR:     *_result_v1);
+// ATTR:     (*_result_v0),
+// ATTR:     (*_result_v1));
 // ATTR: }
 
 def AttrC : TestAttr<"TestF"> {
@@ -278,10 +278,10 @@
 // TYPE:   if (::mlir::failed(_result_v3))
 // TYPE:     return {};
 // TYPE:   return TestDType::get(odsParser.getContext(),
-// TYPE:                         *_result_v0,
-// TYPE:                         *_result_v1,
-// TYPE:                         *_result_v2,
-// TYPE:                         *_result_v3);
+// TYPE:                         (*_result_v0),
+// TYPE:                         (*_result_v1),
+// TYPE:                         (*_result_v2),
+// TYPE:                         (*_result_v3));
 // TYPE: }
 
 // TYPE: void TestDType::print(::mlir::AsmPrinter &odsPrinter) const {
@@ -369,10 +369,10 @@
 // TYPE:       return {};
 // TYPE:   }
 // TYPE:   return TestEType::get(odsParser.getContext(),
-// TYPE:     *_result_v0,
-// TYPE:     *_result_v1,
-// TYPE:     *_result_v2,
-// TYPE:     *_result_v3);
+// TYPE:     (*_result_v0),
+// TYPE:     (*_result_v1),
+// TYPE:     (*_result_v2),
+// TYPE:     (*_result_v3));
 // TYPE: }
 
 // TYPE: void TestEType::print(::mlir::AsmPrinter &odsPrinter) const {
@@ -535,3 +535,19 @@
   let mnemonic = "type_j";
   let assemblyFormat = "custom<A>($a) custom<B>($b, ref($a))";
 }
+
+// TYPE: ::mlir::Type TestMType::parse
+// TYPE: FailureOr<float> _result_a
+// TYPE: return TestMType::get
+// TYPE: static_cast<int>((*_result_a))
+
+def ConvertFromStorageParameter : TypeParameter<"int", ""> {
+  let cppStorageType = "float";
+  let convertFromStorage = "static_cast<int>($_self)";
+}
+
+def TypeK : TestType<"TestM"> {
+  let parameters = (ins ConvertFromStorageParameter:$a);
+  let mnemonic = "type_k";
+  let assemblyFormat = "$a";
+}
diff --git a/mlir/tools/mlir-tblgen/AttrOrTypeFormatGen.cpp b/mlir/tools/mlir-tblgen/AttrOrTypeFormatGen.cpp
--- a/mlir/tools/mlir-tblgen/AttrOrTypeFormatGen.cpp
+++ b/mlir/tools/mlir-tblgen/AttrOrTypeFormatGen.cpp
@@ -297,18 +297,21 @@
   }
   for (const AttrOrTypeParameter &param : params) {
     os << ",\n    ";
+    std::string paramSelfStr;
+    llvm::raw_string_ostream selfOs(paramSelfStr);
     if (param.isOptional()) {
-      os << formatv("_result_{0}.value_or(", param.getName());
+      selfOs << formatv("(_result_{0}.value_or(", param.getName());
       if (Optional<StringRef> defaultValue = param.getDefaultValue())
-        os << tgfmt(*defaultValue, &ctx);
+        selfOs << tgfmt(*defaultValue, &ctx);
       else
-        os << param.getCppStorageType() << "()";
-      os << ")";
+        selfOs << param.getCppStorageType() << "()";
+      selfOs << "))";
     } else if (isa<AttributeSelfTypeParameter>(param)) {
-      os << tgfmt("$_type", &ctx);
+      selfOs << tgfmt("$_type", &ctx);
     } else {
-      os << formatv("*_result_{0}", param.getName());
+      selfOs << formatv("(*_result_{0})", param.getName());
     }
+    os << tgfmt(param.getConvertFromStorage(), &ctx.withSelf(selfOs.str()));
   }
   os << ");";
 }