Layernorm backward regression in triton 3.4.0 release candidate

[davidberard98]

🐛 Describe the bug

FYI: we're seeing a regression in the layernorm backward kernel on shapes 4096 < x <= 8192. See https://github.com/pytorch-labs/tritonbench/issues/264 for details. The regression is caused by register spilling exposed by an LLVM change.

Reproduce

See repro in https://github.com/pytorch-labs/tritonbench/issues/264

Versions

Environment Report:
-------------------
Operating System: Linux-6.4.3-0_fbk15_hardened_2630_gf27365f948db-x86_64-with-glibc2.34
Python version: 3.12.11
Liger Kernel version: 0.5.10
PyTorch version: 2.9.0a0+gitc13a346
CUDA version: 12.6
HIP(ROCm) version: Not available
Triton version: 3.4.0
Transformers version: 4.46.1
XPU version: XPU Not Available