From 2e824585cab9501539df5052d75e518f6110c6fa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dani=C3=ABl=20de=20Kok?= <me@danieldk.eu>
Date: Thu, 28 May 2026 18:39:03 +0000
Subject: [PATCH] kernels: order no C++ tag before C++11 tag

---
 kernels/src/kernels/variants.py |  5 +++--
 kernels/tests/test_variants.py  | 25 +++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/kernels/src/kernels/variants.py b/kernels/src/kernels/variants.py
index 0a8da8c0..bb868566 100644
--- a/kernels/src/kernels/variants.py
+++ b/kernels/src/kernels/variants.py
@@ -490,7 +490,7 @@ def _sort_variants(
     1. AcceptedVariant before RejectedVariant.
     2. Torch stable ABI arch kernels, with highest compatible version first,
        then highest compatible CUDA version.
-    2. Torch arch kernels with with the highest compatible CUDA version.
+    2. Torch arch kernels (tagless before C++ ABI-tagged) with the highest compatible CUDA version.
     3. tvm-ffi arch kernels with with the highest compatible CUDA version.
     4. Torch noarch kernels.
     5. Old Torch universal kernels.
@@ -510,7 +510,8 @@ def sort_key(vs: Decision) -> tuple[int, ...]:
                 )
             elif isinstance(v.framework, Torch):
                 framework_order = 1
-                abi_version_order = (0, 0)
+                # Prefer tagless (cxx11_abi is None) over ABI-tagged.
+                abi_version_order = (0, 1 if v.framework.cxx11_abi is not None else 0)
             else:
                 framework_order = 2
                 abi_version_order = (0, 0)
diff --git a/kernels/tests/test_variants.py b/kernels/tests/test_variants.py
index a4a0b315..2d04e452 100644
--- a/kernels/tests/test_variants.py
+++ b/kernels/tests/test_variants.py
@@ -505,6 +505,31 @@ def test_resolve_stable_abi_newest_version_preferred():
     assert {vs.variant for vs in trace} == set(variants)
 
 
+def test_resolve_tagless_preferred_over_abi_tagged():
+    # Tagless variant (e.g. torch210-cu128) should be preferred over ABI-tagged
+    # (e.g. torch210-cxx11-cu128) when both are accepted.
+    variants = [
+        parse_variant(s)
+        for s in [
+            "torch210-cxx11-cu128-x86_64-linux",
+            "torch210-cu128-x86_64-linux",
+        ]
+    ]
+    result, trace = _resolve_variant_for_system(
+        variants=variants,
+        selected_backend=CUDA(Version("12.8")),
+        cpu="x86_64",
+        os="linux",
+        torch_version=Version("2.10"),
+        torch_cxx11_abi=True,
+        tvm_ffi_version=None,
+    )
+    assert result != []
+    assert result[0].variant_str == "torch210-cu128-x86_64-linux"
+    assert result == [vs.variant for vs in trace if isinstance(vs, VariantAccepted)]
+    assert {vs.variant for vs in trace} == set(variants)
+
+
 def test_resolve_stable_abi_preferred_over_torch():
     # TorchStableAbi variant is preferred over a regular Torch variant of the same version.
     variants = [