[mlir] Don't emit forward declaration for user defined storage classes

[uenoku]

Summary

Currently DefGen::emitDecl always emits forward declarations of storage classes even for user define ones, which makes it difficult to use template class directly in ODS. This patch changes DefGen not to emit forward decl when genStorageClass is false.

Original discussion: https://discourse.llvm.org/t/use-template-classes-as-user-defined-storage-classes/72015

[rriddle]

If it's just for user defined storage classes, seems reasonable enough to me.

[mehdi_amini]

LG, do you have commit access?

[uenoku]

Update flang.

[uenoku]

LG, do you have commit access?

Yes, thanks!

flang/include/flang/Optimizer/Dialect/FIRType.h

 #include "mlir/IR/BuiltinTypes.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/IR/Type.h"
 
 namespace fir {
 class FIROpsDialect;
 class KindMapping;
 using KindTy = unsigned;
+
+namespace detail {
+struct RecordTypeStorage;
+} // namespace detail
+
 } // namespace fir
 
 //===----------------------------------------------------------------------===//
 // BaseBoxType
 //===----------------------------------------------------------------------===//
 
 namespace fir {
 

mlir/include/mlir/IR/BuiltinAttributes.h

 class FlatSymbolRefAttr;
 class FunctionType;
 class IntegerSet;
 class IntegerType;
 class Location;
 class Operation;
 class RankedTensorType;
 
+namespace detail {
+struct DenseIntOrFPElementsAttrStorage;
+struct DenseStringElementsAttrStorage;
+struct StringAttrStorage;
+} // namespace detail
+
 //===----------------------------------------------------------------------===//
 // Elements Attributes
 //===----------------------------------------------------------------------===//
 
 namespace detail {
 /// Pair of raw pointer and a boolean flag of whether the pointer holds a splat,
 using DenseIterPtrAndSplat = std::pair<const char *, bool>;
 

mlir/include/mlir/IR/BuiltinTypes.h

 class FloatType;
 class IndexType;
 class IntegerType;
 class MemRefType;
 class RankedTensorType;
 class StringAttr;
 class TypeRange;
 
+namespace detail {
+struct FunctionTypeStorage;
+struct IntegerTypeStorage;
+struct TupleTypeStorage;
+} // namespace detail
+
 //===----------------------------------------------------------------------===//
 // FloatType
 //===----------------------------------------------------------------------===//
 
 class FloatType : public Type {
 public:
   using Type::Type;
 

mlir/tools/mlir-tblgen/AttrOrTypeDefGen.cpp

 
 namespace {
 class DefGen {
 public:
   /// Create the attribute or type class.
   DefGen(const AttrOrTypeDef &def);
 
   void emitDecl(raw_ostream &os) const {
-    if (storageCls) {
+    if (storageCls && def.genStorageClass()) {
       NamespaceEmitter ns(os, def.getStorageNamespace());
       os << "struct " << def.getStorageClassName() << ";\n";
     }
     defCls.writeDeclTo(os);
   }
   void emitDef(raw_ostream &os) const {
     if (storageCls && def.genStorageClass()) {
       NamespaceEmitter ns(os, def.getStorageNamespace());