[mlir] Revert to old fold logic in IR::Dialect::add{Types, Attributes…

…}() (llvm#79582)

Fold expressions on Clang are limited to 256 elements. This causes
compilation errors in cases when the amount of elements added exceeds
this limit. Side-step the issue by restoring the original trick that
would use the std::initializer_list. For the record, in our downstream
Clang 16 gives:

mlir/include/mlir/IR/Dialect.h:269:23: fatal error: instantiating fold
expression with 688 arguments exceeded expression nesting limit of 256
    (addType<Args>(), ...);

Partially reverts 26d811b.

Co-authored-by: Nikita Kudriavtsev <[email protected]>

mlir/include/mlir/IR/Dialect.h

@@ -281,7 +281,11 @@ class Dialect {
   /// Register a set of type classes with this dialect.
   template <typename... Args>
   void addTypes() {
-    (addType<Args>(), ...);
+    // This initializer_list argument pack expansion is essentially equal to
+    // using a fold expression with a comma operator. Clang however, refuses
+    // to compile a fold expression with a depth of more than 256 by default.
+    // There seem to be no such limitations for initializer_list.
+    (void)std::initializer_list<int>{0, (addType<Args>(), 0)...};
   }
 
   /// Register a type instance with this dialect.
@@ -292,7 +296,11 @@ class Dialect {
   /// Register a set of attribute classes with this dialect.
   template <typename... Args>
   void addAttributes() {
-    (addAttribute<Args>(), ...);
+    // This initializer_list argument pack expansion is essentially equal to
+    // using a fold expression with a comma operator. Clang however, refuses
+    // to compile a fold expression with a depth of more than 256 by default.
+    // There seem to be no such limitations for initializer_list.
+    (void)std::initializer_list<int>{0, (addAttribute<Args>(), 0)...};
   }
 
   /// Register an attribute instance with this dialect.