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ggml-cpu : fix leftover handling in ggml_vec_scale_f32 for SVE (#16443)

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This commit updates the leftover handling in ggml_vec_scale_f32.

The motivation for this is that the code currently incorrectly assumes
there would be fewer than ggml_f32_epr leftover elements. However,
since the main loop processes 2*ggml_f32_epr elements per iteration
, there can be up to (2*ggml_f32_epr - 1) leftover elements.

The original single-pass leftover code could only process ggml_f32_epr
elements, leaving some elements unscaled.

Example scenario with 256-bit SVE:
```
ggml_f32_epr  = 8 (elements per register)
ggml_f32_step = 16 (two registers per iteration)
n             = 25
np            = 16
leftovers     = 9 elements (16-24)

Original    : processes only elements 16-23, misses element 24
This commit : loop processes elements 16-23, then element 24
```

Refs: https://github.com/ggml-org/llama.cpp/actions/runs/18070620247/job/51419855630
This commit is contained in:
Daniel Bevenius
2025-10-06 14:17:12 +02:00
committed by GitHub
parent 1d49ca3759
commit a80ff183ab
1 changed files with 4 additions and 4 deletions
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8
ggml/src/ggml-cpu/vec.h
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@@ -654,11 +654,11 @@ inline static void ggml_vec_scale_f32(const int n, float * y, const float v) {
}
// leftovers
// maximum number of leftover elements will be less that ggml_f32_epr. Apply predicated svmad on available elements only
if (np < n) {
svbool_t pg = svwhilelt_b32(np, n);
ay1 = svld1_f32(pg, y + np);
for (int i = np; i < n; i += ggml_f32_epr) {
svbool_t pg = svwhilelt_b32(i, n);
ay1 = svld1_f32(pg, y + i);
ay1 = svmul_f32_m(pg, ay1, vx);
svst1_f32(pg, y + np, ay1);
svst1_f32(pg, y + i, ay1);
}
#elif defined(__riscv_v_intrinsic)
for (int i = 0, avl; i < n; i += avl) {