[SYCL] Fix reorder MMVQ assert on unaligned vocab sizes (ggml-org#22035)

* [SYCL] Fix reorder MMVQ assert on unaligned vocab sizes

The reorder mul_mat_vec_q dispatchers for Q4_0, Q8_0, Q4_K, and Q6_K
asserted that block_num_y was a multiple of 16 subgroups. Models with
a vocab size not divisible by 16 (for example HY-MT at 120818) aborted
on model load when the output projection tripped the assert.

I replaced the assert with padding: block_num_y now rounds up to a
whole number of subgroup-sized workgroups. The kernel already has the
row bounds check (`if (row >= nrows) return;`) so the extra padded
threads early-exit cleanly. Row values are uniform across a subgroup
so the collective reduce stays safe.

For aligned vocab sizes the padded block_num_y equals the old value,
so the kernel launch is identical and there is no regression.

Thanks to @arthw for flagging the relationship to ggml-org#21527.

Fixes ggml-org#22020.

AI assisted coding, tested on Intel B70 hardware.

* sycl: use WARP_SIZE for num_subgroups in reorder MMVQ launches

Replaces the hardcoded 16 with WARP_SIZE in the four reorder_mul_mat_vec
launch helpers (Q4_0, Q8_0, Q4_K, Q6_K). Compile-time no-op on the Intel
target where WARP_SIZE is 16, but makes the relationship to subgroup
size explicit. Per review by @NeoZhangJianyu on ggml-org#22035.

Assisted by Claude.

Author: PMZFX

ggml/src/ggml-sycl/mmvq.cpp

@@ -537,9 +537,9 @@ static void mul_mat_vec_q_iq4_xs_q8_1(const void *__restrict__ vx,
 static void reorder_mul_mat_vec_q4_0_q8_1_sycl(const void * vx, const void * vy, float * dst, const int ncols,
                                                     const int nrows, dpct::queue_ptr stream) {
     GGML_ASSERT(ncols % QK4_0 == 0);
-    const int        block_num_y   = ceil_div(nrows, GGML_SYCL_MMV_Y);
-    constexpr size_t num_subgroups = 16;
-    GGML_ASSERT(block_num_y % num_subgroups == 0);
+    // Round up to a whole number of subgroup-sized workgroups; out-of-range rows are skipped inside the kernel.
+    constexpr size_t num_subgroups = WARP_SIZE;
+    const int        block_num_y   = ceil_div(nrows, GGML_SYCL_MMV_Y * (int) num_subgroups) * (int) num_subgroups;
 
     const sycl::range<3> global_size(1, GGML_SYCL_MMV_Y, (block_num_y * WARP_SIZE));
     const sycl::range<3> workgroup_size(1, GGML_SYCL_MMV_Y, num_subgroups * WARP_SIZE);
@@ -682,9 +682,9 @@ static void mul_mat_vec_q5_1_q8_1_sycl(const void *vx, const void *vy,
 static void reorder_mul_mat_vec_q8_0_q8_1_sycl(const void * vx, const void * vy, float * dst, const int ncols,
                                                     const int nrows, dpct::queue_ptr stream) {
     GGML_ASSERT(ncols % QK8_0 == 0);
-    const int        block_num_y   = ceil_div(nrows, GGML_SYCL_MMV_Y);
-    constexpr size_t num_subgroups = 16;
-    GGML_ASSERT(block_num_y % num_subgroups == 0);
+    // Round up to a whole number of subgroup-sized workgroups; out-of-range rows are skipped inside the kernel.
+    constexpr size_t num_subgroups = WARP_SIZE;
+    const int        block_num_y   = ceil_div(nrows, GGML_SYCL_MMV_Y * (int) num_subgroups) * (int) num_subgroups;
 
     const sycl::range<3> global_size(1, GGML_SYCL_MMV_Y, (block_num_y * WARP_SIZE));
     const sycl::range<3> workgroup_size(1, GGML_SYCL_MMV_Y, num_subgroups * WARP_SIZE);
@@ -798,9 +798,9 @@ static void reorder_mul_mat_vec_q4_k_q8_1_sycl(const void * vx, const void * vy,
     const int nrows, dpct::queue_ptr stream) {
     GGML_ASSERT(ncols % QK_K == 0);
 
-    const int block_num_y = ceil_div(nrows, GGML_SYCL_MMV_Y);
-    constexpr size_t num_subgroups = 16;
-    GGML_ASSERT(block_num_y % num_subgroups == 0);
+    // Round up to a whole number of subgroup-sized workgroups; out-of-range rows are skipped inside the kernel.
+    constexpr size_t num_subgroups = WARP_SIZE;
+    const int block_num_y = ceil_div(nrows, GGML_SYCL_MMV_Y * (int) num_subgroups) * (int) num_subgroups;
 
     const sycl::range<3> global_size(1, GGML_SYCL_MMV_Y, block_num_y * WARP_SIZE);
     const sycl::range<3> workgroup_size(1, GGML_SYCL_MMV_Y, num_subgroups * WARP_SIZE);
@@ -842,9 +842,9 @@ static void mul_mat_vec_q5_K_q8_1_sycl(const void *vx, const void *vy,
 static void reorder_mul_mat_vec_q6_k_q8_1_sycl(const void * vx, const void * vy, float * dst, const int ncols,
                                                const int nrows, dpct::queue_ptr stream) {
     GGML_ASSERT(ncols % QK_K == 0);
-    const int        block_num_y   = ceil_div(nrows, GGML_SYCL_MMV_Y);
-    constexpr size_t num_subgroups = 16;
-    GGML_ASSERT(block_num_y % num_subgroups == 0);
+    // Round up to a whole number of subgroup-sized workgroups; out-of-range rows are skipped inside the kernel.
+    constexpr size_t num_subgroups = WARP_SIZE;
+    const int        block_num_y   = ceil_div(nrows, GGML_SYCL_MMV_Y * (int) num_subgroups) * (int) num_subgroups;
 
     const sycl::range<3> global_size(1, GGML_SYCL_MMV_Y, block_num_y * WARP_SIZE);
     const sycl::range<3> workgroup_size(1, GGML_SYCL_MMV_Y, num_subgroups * WARP_SIZE);