[llvm-branch-commits] [clang] [CIR] Record why the CUDA registration attribute parses itself (PR #220893)

[Henrich Lauko via llvm-branch-commits]

https://github.com/xlauko created https://github.com/llvm/llvm-project/pull/220893

hasCustomAssemblyFormat with no explanation invites the question of whether a
declarative assemblyFormat would do, and the answer is not obvious from the
parameter list. It would not. The three flags print as presence-only keywords
and parse in any order, while an optional group anchored on a `bool`
parameter parses and prints a value, so the group would spell `extern true`.
MLIR has no presence-only flag for `bool` in an attribute format, unlike
UnitAttr in an operation format. struct(params) does round-trip, but spells
the attribute `<device_side_name = "i", kind = Variable, isExtern = true>`
instead of `<i, Variable, extern>`.

NFC.

---

Stacked on #220892. Based on `users/xlauko/cir-enum-13-inline-mnemonic`, so the diff shown is this commit alone.


>From 7234761bf1869f98d9e66c70b95407795ebf482b Mon Sep 17 00:00:00 2001
From: Henrich Lauko <hlauko at nvidia.com>
Date: Thu, 3 Sep 2026 11:29:23 +0000
Subject: [PATCH] [CIR] Record why the CUDA registration attribute parses
 itself

hasCustomAssemblyFormat with no explanation invites the question of whether a
declarative assemblyFormat would do, and the answer is not obvious from the
parameter list. It would not. The three flags print as presence-only keywords
and parse in any order, while an optional group anchored on a `bool`
parameter parses and prints a value, so the group would spell `extern true`.
MLIR has no presence-only flag for `bool` in an attribute format, unlike
UnitAttr in an operation format. struct(params) does round-trip, but spells
the attribute `<device_side_name = "i", kind = Variable, isExtern = true>`
instead of `<i, Variable, extern>`.

NFC.
---
 clang/include/clang/CIR/Dialect/IR/CIRCUDAAttrs.td | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/clang/include/clang/CIR/Dialect/IR/CIRCUDAAttrs.td b/clang/include/clang/CIR/Dialect/IR/CIRCUDAAttrs.td
index 3362ff1812e34..c3662a92a43b8 100644
--- a/clang/include/clang/CIR/Dialect/IR/CIRCUDAAttrs.td
+++ b/clang/include/clang/CIR/Dialect/IR/CIRCUDAAttrs.td
@@ -92,6 +92,11 @@ def CIR_CUDAVarRegistrationInfoAttr : CIR_Attr<"CUDAVarRegistrationInfo", "cu.va
     "bool":$isManaged
   );
 
+  // Not expressible as a declarative assemblyFormat. The three flags print as
+  // presence-only keywords and parse in any order, whereas an optional group
+  // anchored on a `bool` parameter parses and prints a value, so `extern`
+  // would have to spell `extern true`. struct(params) round-trips but costs
+  // the compact syntax.
   let hasCustomAssemblyFormat = 1;
 }