Minor hardcoded values with device built-in warpSize#784
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abagusetty
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Jun 12, 2026
abagusetty
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- Replace the hardcoded values with device built-ins
- Fix a test to replace cupy.linalg to numpy.linalg
added 3 commits
June 11, 2026 21:29
Pure CUDA refactor that substitutes hardcoded warp-size assumptions
in device-side kernels with the CUDA/HIP `warpSize` device-runtime
built-in. No HIP-specific code is introduced; all changes remain
correct on NVIDIA (warpSize=32) and become portable to architectures
where the warp/wavefront size differs (e.g. AMD CDNA gfx9xx with
wavefront=64).
This is a prerequisite for the companion `hip` branch (a HIP/ROCm
build) to produce correct results on wavefront-64 AMD GPUs. The two
branches are intentionally independent so the warpSize cleanup can
land on master without coupling to the HIP build system.
Device-side substitutions (warpSize is a runtime constant; safe in
__global__ / __device__ contexts):
- gpu4pyscf/lib/ecp/common.cu: classic block_reduce pattern --
shared-memory reduce loop bound (s >= 32 -> s >= warpSize),
warp-leader gate (tid < 32 -> tid < warpSize), and the
intra-warp __shfl_down_sync sequence (16/8/4/2/1 unrolled ->
for offset = warpSize/2; offset > 0; offset >>= 1).
- gpu4pyscf/lib/gvhf-md/{unrolled_md_j.cu, unrolled_md_j_4dm.cu,
md_contract_j.cu}: 25 occurrences of `lane_id = X % 32` ->
`lane_id = X % warpSize`.
- gpu4pyscf/lib/multigrid/multigrid_v2/evaluation.cuh: warp-stride
reduction loop (_o = 16 -> _o = warpSize/2), warp-leader test
(tid & 31 -> tid % warpSize), warp index (tid >> 5 ->
tid / warpSize). Centralized the constexpr n_warps divisor
into a named constant.
Host-side / constexpr substitutions (warpSize is device-only so a
named constant is used instead):
- gpu4pyscf/lib/gvhf-md/md_j_driver.cu: qd_offset_for_threads
32-element alignment now uses a named WARP_SIZE_HOST constant
derived from the assumed warp width.
- gpu4pyscf/lib/pbc/{int3c2e_create_tasks.cuh,
int3c2e_create_tasks_o1.cuh, int3c2e.cuh, ft_ao.cuh, ft_ao.cu},
gpu4pyscf/lib/multigrid/multigrid.cuh: existing
`#define WARP_SIZE 32` directives wrapped in `#ifndef WARP_SIZE`
so the build system can override the value (e.g. -DWARP_SIZE=64)
for future wider-wavefront targets.
All changes are zero-cost on NVIDIA and unlock correct portability.
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