[Mlir-commits] [mlir] [mlir] Revert to old fold logic in IR::Dialect::addTypes() (PR #79582)

[Andrei Golubev]

https://github.com/andrey-golubev created https://github.com/llvm/llvm-project/pull/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 instance, 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 26d811b3ecd2fa1ca3d9b41e17fb42b8c7ad03d6.

>From 75f52c8e489487bbff1cd3d0b72eb9b704ebd23a Mon Sep 17 00:00:00 2001
From: "Golubev, Andrey" <andrey.golubev at intel.com>
Date: Fri, 26 Jan 2024 11:44:23 +0000
Subject: [PATCH] [mlir] Revert to old fold logic in IR::Dialect::addTypes()

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 instance, 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 26d811b3ecd2fa1ca3d9b41e17fb42b8c7ad03d6.
---
 mlir/include/mlir/IR/Dialect.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mlir/include/mlir/IR/Dialect.h b/mlir/include/mlir/IR/Dialect.h
index 45f29f37dd3b97c..9fe1e1c89b228cb 100644
--- a/mlir/include/mlir/IR/Dialect.h
+++ b/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.