Support struct-backed type

example/ExampleDialect.td

@@ -361,3 +361,42 @@ def BufferCompareOp : Op<ExampleDialect, "buffer.compare.op", [WillReturn, NoUnw
     Both arguments get a parameter attribute, as well as return value
   }];
 }
+
+def StructBackedType : DialectType<ExampleDialect, "struct.backed"> {
+  let summary = "a custom struct-backed type";
+  let description = [{
+    Test that a struct-backed type works correctly.
+  }];
+  let typeArguments = (args AttrI32:$field0, AttrI32:$field1, AttrI32:$field2);
+  let representation = (repr_struct (IntegerType 41));
+  let structPrefix = "sb_";
+
+  let defaultGetterHasExplicitContextArgument = 1;
+}
+
+def DummyStructBackedInpOp : Op<ExampleDialect, "struct.backed.inp.op", [WillReturn]> {
+  let summary = "a custom op using input arg with struct-backed type";
+  let description = [{
+    Test that an operation that takes argument with struct-backed type works correctly.
+  }];
+  let arguments = (ins
+    StructBackedType:$inp
+  );
+  let results = (outs
+    I32:$ret
+  );
+}
+
+def DummyStructBackedOutpOp : Op<ExampleDialect, "struct.backed.outp.op", [WillReturn]> {
+  let summary = "a custom op returning value with struct-backed type";
+  let description = [{
+    Test that an operation that returns value with struct-backed type works correctly.
+  }];
+  let arguments = (ins
+    I32:$extra_arg
+  );
+  let results = (outs
+    StructBackedType:$outp
+  );
+  let defaultBuilderHasExplicitResultType = true;
+}

example/ExampleMain.cpp

@@ -149,6 +149,10 @@ void createFunctionExample(Module &module, const Twine &name) {
 
   b.create<xd::cpp::StringAttrOp>("Hello world!");
 
+  xd::cpp::StructBackedType *structBackedTy = xd::cpp::StructBackedType::get(bb->getContext(), 1, 0, 2);
+  auto *structBackedVal = b.create<xd::cpp::DummyStructBackedOutpOp>(structBackedTy, b.getInt32(42), "gen.struct.backed.val");
+  b.create<xd::cpp::DummyStructBackedInpOp>(structBackedVal, "consume.struct.backed.val");
+
   b.CreateRetVoid();
 }
 

include/llvm-dialects/Dialect/Dialect.td

@@ -215,6 +215,9 @@ def F64 : SpecialBuiltinType<"Double">;
 def F32 : SpecialBuiltinType<"Float">;
 def F16 : SpecialBuiltinType<"Half">;
 
+def repr_targetext;
+def repr_struct;
+
 /// All types that are defined by a dialect are derived from this class.
 class DialectType<Dialect dialect_, string mnemonic_> : Type, Predicate {
   dag typeArguments = ?;
@@ -229,6 +232,14 @@ class DialectType<Dialect dialect_, string mnemonic_> : Type, Predicate {
 
   string summary = ?;
   string description = ?;
+
+  /// How the dialect type is represented in LLVM IR:
+  ///  - (repr_targetext): use a TargetExtType (the default)
+  ///  - (repr_struct <type>): use a StructType with the given type as the
+  ///    discriminant; the discriminant should be a type that cannot naturally
+  ///    appear elsewhere, e.g. (repr_struct (IntegerType 41))
+  dag representation = (repr_targetext);
+  string structPrefix = "";
 }
 
 def and;

include/llvm-dialects/TableGen/DialectType.h

@@ -75,6 +75,10 @@ class DialectType : public BaseCppPredicate {
   std::string m_context;
   std::vector<GetterArg> m_getterArguments;
   unsigned m_argBegin = 0;
+
+  bool m_structBacked = false;
+  unsigned m_structSentinelBitWidth;
+  std::string m_structPrefix;
 };
 
 } // namespace llvm_dialects