[BUG] CUDA compiler warning for CUDF_HOST_DEVICE on constexpr variables

[bdice]

Describe the bug

The CUDA compiler 13.3 emits warning #1835-D when CUDF_HOST_DEVICE annotates a namespace-scope constexpr variable because the macro expands to the function-only __host__ __device__ attributes.

PR #24237 removes the invalid annotation from all known cases:

• cpp/include/cudf/join/join.hpp: JoinNoMatch
• cpp/src/groupby/hash/compute_shared_memory_aggs.cu: ALIGNMENT
• cpp/src/groupby/hash/helpers.cuh: GROUPBY_CG_SIZE
• cpp/src/groupby/hash/helpers.cuh: GROUPBY_BUCKET_SIZE
• cpp/src/groupby/hash/helpers.cuh: GROUPBY_BLOCK_SIZE
• cpp/src/groupby/hash/helpers.cuh: GROUPBY_CARDINALITY_THRESHOLD
• cpp/src/groupby/hash/helpers.cuh: GROUPBY_SHM_MAX_ELEMENTS
• cpp/src/groupby/hash/helpers.cuh: valid_extent
• cpp/src/join/key_remapping.cu: KEY_REMAP_BLOCK_SIZE

An audit of CUDF_HOST_DEVICE uses found no additional namespace-scope constexpr variables with the annotation.

Steps/Code to reproduce bug

#define CUDF_HOST_DEVICE __host__ __device__

CUDF_HOST_DEVICE constexpr int value = 42;

int main() { return value == 42 ? 0 : 1; }

Compile with the CUDA compiler 13.3:

nvcc -std=c++20 --display-error-number -c reproducer.cu

The CUDA compiler emits:

warning #1835-D: attribute "__host__" does not apply here

Promoting diagnostic 1835 to an error makes the compilation fail:

nvcc -std=c++20 --diag-error=1835 -c reproducer.cu

Expected behavior

Namespace-scope constexpr variables are not annotated with function-only attributes, and the CUDA compiler does not emit diagnostic 1835. The variables remain usable in host and device constant expressions without the annotation.

Environment overview

• CUDA compiler 13.3.73
• Standalone compiler reproducer; no cuDF installation is required

[PointKernel]

@bdice where did you find this issue? Was it in our CI?