vulkan : dequant q8_0 KV once in coopmat1 (#25494)

* vulkan : dequant q8_0 KV once in coopmat1

Assisted-by: Claude (Opus 4.8)

* vulkan : fall back instead of aborting when FA scratch exceeds maxStorageBufferRange

* vulkan : require KV-cache layout in FA dequant path

Assisted-by: Claude (Opus 4.8)

* vulkan : skip FA dequant path on coopmat2

Assisted-by: Claude (Opus 4.8)

* tests : add contiguously-allocated quant K/V FA tests

Assisted-by: Claude (Opus 4.8)

* vulkan : trim comments

* vulkan : tighten permutation checks for FA path

* vulkan : set prealloc_x_need_sync after the FA dispatch

* vulkan : exclude Intel Xe1 from FA dequant path

ggml/src/ggml-vulkan/vulkan-shaders/dequant_q8_0.comp

@@ -18,7 +18,18 @@ void main() {
         return;
     }
 
+#ifdef DEQUANT_TRANSPOSE
+    // read [HS, NH, KV, NS], write [HS, KV, NH, NS]
+    const uint HS = p.M, NH = p.K, KVn = p.stride_a;
+    const uint e0 = ib * 32;
+    const uint b_idx = (e0 % HS)
+                     + ((e0 / (HS * NH)) % KVn) * HS
+                     + ((e0 / HS) % NH) * (HS * KVn)
+                     + (e0 / (HS * NH * KVn)) * (HS * KVn * NH)
+                     + 16 * il;
+#else
     const uint b_idx = 1024*i + 32*ir + 16*il;
+#endif
 
     const float d = float(data_a[ib].d);
 

ggml/src/ggml-vulkan/vulkan-shaders/vulkan-shaders-gen.cpp

@@ -780,6 +780,10 @@ void process_shaders() {
         if (tname != "f16" && tname != "bf16") {
             string_to_spv("dequant_" + tname, "dequant_" + tname + ".comp", merge_maps(base_dict, {{data_a_key, "1"}, {"D_TYPE", "float16_t"}}));
         }
+        // Fused dequant+transpose variant for FA quant-KV (per-head-contiguous f16 scratch).
+        if (tname == "q8_0") {
+            string_to_spv("dequant_" + tname + "_transpose", "dequant_" + tname + ".comp", merge_maps(base_dict, {{data_a_key, "1"}, {"D_TYPE", "float16_t"}, {"DEQUANT_TRANSPOSE", "1"}}));
+        }
 
         shader = (tname == "f32" || tname == "f16" || tname == "bf16") ? "get_rows.comp" : "get_rows_quant.comp";