sycl: fuse RMS_NORM + MUL

[Titaniumtown]

Overview

Port of cuda path ggml_cuda_op_rms_norm_fused to SYCL.

Also adds a function ggml_sycl_can_fuse that can be used in future fusion PRs that I am am working on. This is analogous to the cuda ggml_cuda_can_fuse.

Additional information

Benchmarked on an Arc B70:

master @ 0278d83:

| model                          |       size |     params | backend    | ngl |  fa |            test |                  t/s |
|------------------------------ | ---------: | ---------: | ---------- | --: | --: | --------------: | -------------------: |
| qwen35 27B Q4_K - Medium       |  16.67 GiB |    27.32 B | SYCL       | 999 |   1 |           pp512 |        849.40 ± 1.34 |
| qwen35 27B Q4_K - Medium       |  16.67 GiB |    27.32 B | SYCL       | 999 |   1 |          pp2048 |        845.89 ± 1.58 |
| qwen35 27B Q4_K - Medium       |  16.67 GiB |    27.32 B | SYCL       | 999 |   1 |           tg128 |         23.37 ± 0.02 |

Patched — master + rms_norm+mul fusion:

| model                          |       size |     params | backend    | ngl |  fa |            test |                  t/s |
| ------------------------------ | ---------: | ---------: | ---------- | --: | --: | --------------: | -------------------: |
| qwen35 27B Q4_K - Medium       |  16.67 GiB |    27.32 B | SYCL       | 999 |   1 |           pp512 |        854.02 ± 1.54 |
| qwen35 27B Q4_K - Medium       |  16.67 GiB |    27.32 B | SYCL       | 999 |   1 |          pp2048 |        851.84 ± 0.72 |
| qwen35 27B Q4_K - Medium       |  16.67 GiB |    27.32 B | SYCL       | 999 |   1 |           tg128 |         23.48 ± 0.02 |

Uplift: pp512 +0.54%, pp2048 +0.70%, tg128 +0.47%.

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: YES - Claude Opus 4.8 was used to help understand the codebase and testing.

[arthw]

With Qwen3.5-4B-Q4_K_M.gguf on B60:

Test	fa	Base t/s	Primary t/s	Increase Rate (Primary vs Base)
pp512	0	1048.44	1056.17	0.74%
pp512	1	1048.79	1055.80	0.67%
tg128	0	80.09	81.02	1.16%
tg128	1	80.60	81.65	1.30%

[Titaniumtown]

Ready for review!

[arthw]

It's good job!

Thank you!

[malsbat]

@Titaniumtown, I was wondering what other fusions you have in the works? I was looking at bringing some work we had done earlier up to date and found this PR that already did the RMS_NORM+MUL.

I don't want to duplicate effort if you're already working on these ones:

• RMS_NORM+MUL+ADD: https://github.com/aicss-genai/llama.cpp/blob/aicss-genai-fork/aicss-genai/patches/0012-sycl-extend-graph-fusion.patch
• UNARY+MUL: https://github.com/aicss-genai/llama.cpp/blob/aicss-genai-fork/aicss-genai/patches/0011-sycl-fuse-unary-mul.patch

[Titaniumtown]

@malsbat I have both of those already locally. I can submit PRs for those.

[malsbat]

@malsbat I have both of those already locally. I can submit PRs for those.

Great, looking forward to those PRs!