Vulkan: some improvement on mul_mat_iq2_xs (#18031)

* Some improvement on mul_mat_iq2_xs

Refactor calculations for db values and grid data to optimize performance and reduce redundancy.

* Fix trailing whitespace

Author: lovedheart

ggml/src/ggml-vulkan/vulkan-shaders/mul_mat_vec_iq2_xs.comp

@@ -11,36 +11,54 @@ void calc_superblock(const uint a_offset, const uint b_offset, const uint itid,
     const uint y_idx = i * QUANT_K + 16 * itid;
     const uint nibble_shift = 4 * (itid & 1);
     const uint ib32 = itid / 2; // 0..7
-
     uint ibi = a_offset / QUANT_K + first_row * num_blocks_per_row + i;
+    // Precompute db multiplication factors
+    float db_vals[NUM_ROWS];
     [[unroll]] for (uint n = 0; n < num_rows; ++n) {
         const float d = float(data_a[ibi].d);
-        const uint scale = (data_a[ibi].scales[ib32] >> nibble_shift) & 0xF;
-        const float db = d * (0.5 + scale) * 0.25;
-
+        const uint scale_raw = data_a[ibi].scales[ib32];
+        const uint scale = (scale_raw >> nibble_shift) & 0xF;
+        // Merge constant calculations d * (0.5 + scale) * 0.25 = d*0.125 + d*scale*0.25
+        db_vals[n] = d * (0.125f + float(scale) * 0.25f);
+        ibi += num_blocks_per_row;
+    }
+    ibi = a_offset / QUANT_K + first_row * num_blocks_per_row + i;
+    [[unroll]] for (uint n = 0; n < num_rows; ++n) {
+        // Preload grid and sign data for all l values
+        vec4 grid0_vals[2], grid1_vals[2];
+        uint sign_vals[2], sign7_vals[2];
         [[unroll]] for (uint l = 0; l < 2; ++l) {
             const uint qs = data_a[ibi].qs[2 * itid + l];
-            const uint sign = qs >> 9;
-            const uint sign7 = bitCount(sign);
-            const vec4 grid0 = vec4(unpack8(iq2xs_grid[qs & 511].x));
-            const vec4 grid1 = vec4(unpack8(iq2xs_grid[qs & 511].y));
-
-            [[unroll]] for (uint j = 0; j < NUM_COLS; ++j) {
-                vec4 b0 = vec4(data_b_v4[(j*p.batch_stride_b + b_offset + y_idx) / 4 + 2*l + 0]);
-                vec4 b4 = vec4(data_b_v4[(j*p.batch_stride_b + b_offset + y_idx) / 4 + 2*l + 1]);
-
-                FLOAT_TYPE sum =
-                      fma(FLOAT_TYPE(b0.x), FLOAT_TYPE((sign &   1) != 0 ? -grid0.x : grid0.x),
-                      fma(FLOAT_TYPE(b0.y), FLOAT_TYPE((sign &   2) != 0 ? -grid0.y : grid0.y),
-                      fma(FLOAT_TYPE(b0.z), FLOAT_TYPE((sign &   4) != 0 ? -grid0.z : grid0.z),
-                      fma(FLOAT_TYPE(b0.w), FLOAT_TYPE((sign &   8) != 0 ? -grid0.w : grid0.w),
-                      fma(FLOAT_TYPE(b4.x), FLOAT_TYPE((sign &  16) != 0 ? -grid1.x : grid1.x),
-                      fma(FLOAT_TYPE(b4.y), FLOAT_TYPE((sign &  32) != 0 ? -grid1.y : grid1.y),
-                      fma(FLOAT_TYPE(b4.z), FLOAT_TYPE((sign &  64) != 0 ? -grid1.z : grid1.z),
-                      fma(FLOAT_TYPE(b4.w), FLOAT_TYPE((sign7 &  1) != 0 ? -grid1.w : grid1.w),
-                      FLOAT_TYPE(0.0)))))))));
-                temp[j][n] = fma(db, sum, temp[j][n]);
+            sign_vals[l] = qs >> 9;
+            sign7_vals[l] = bitCount(sign_vals[l]);
+            const uvec2 grid_data = iq2xs_grid[qs & 511];
+            grid0_vals[l] = vec4(unpack8(grid_data.x));
+            grid1_vals[l] = vec4(unpack8(grid_data.y));
+        }
+        // Preload B data for all j columns (reduce repeated index calculations)
+        [[unroll]] for (uint j = 0; j < NUM_COLS; ++j) {
+            FLOAT_TYPE sum = FLOAT_TYPE(0.0);
+            [[unroll]] for (uint l = 0; l < 2; ++l) {
+                const uint sign = sign_vals[l];
+                const uint sign7 = sign7_vals[l];
+                const vec4 grid0 = grid0_vals[l];
+                const vec4 grid1 = grid1_vals[l];
+                // Precompute indices
+                const uint b_idx = (j * p.batch_stride_b + b_offset + y_idx) / 4 + 2 * l;
+                const vec4 b0 = vec4(data_b_v4[b_idx + 0]);
+                const vec4 b4 = vec4(data_b_v4[b_idx + 1]);
+                sum +=
+                    fma(FLOAT_TYPE(b0.x), FLOAT_TYPE((sign &   1) != 0 ? -grid0.x : grid0.x),
+                    fma(FLOAT_TYPE(b0.y), FLOAT_TYPE((sign &   2) != 0 ? -grid0.y : grid0.y),
+                    fma(FLOAT_TYPE(b0.z), FLOAT_TYPE((sign &   4) != 0 ? -grid0.z : grid0.z),
+                    fma(FLOAT_TYPE(b0.w), FLOAT_TYPE((sign &   8) != 0 ? -grid0.w : grid0.w),
+                    fma(FLOAT_TYPE(b4.x), FLOAT_TYPE((sign &  16) != 0 ? -grid1.x : grid1.x),
+                    fma(FLOAT_TYPE(b4.y), FLOAT_TYPE((sign &  32) != 0 ? -grid1.y : grid1.y),
+                    fma(FLOAT_TYPE(b4.z), FLOAT_TYPE((sign &  64) != 0 ? -grid1.z : grid1.z),
+                    fma(FLOAT_TYPE(b4.w), FLOAT_TYPE((sign7 &  1) != 0 ? -grid1.w : grid1.w),
+                    FLOAT_TYPE(0.0)))))))));
             }
+            temp[j][n] = fma(FLOAT_TYPE(db_vals[n]), sum, temp[j][n]);
         }
         ibi += num_blocks_per_row;
     }