Vulkan: improve mul_mat_vec_iq1_m (#16907)

* Optimize Vulkan shader for matrix-vector multiplication

* Revert changes on compute_outputs and main

Refactor compute_outputs to handle remaining rows correctly.

* Fix trailing whitespace

ggml/src/ggml-vulkan/vulkan-shaders/mul_mat_vec_iq1_m.comp

@@ -7,35 +7,85 @@ layout(local_size_x_id = 0, local_size_y = 1, local_size_z = 1) in;
 
 FLOAT_TYPE temp[NUM_COLS][NUM_ROWS];
 
-void calc_superblock(const uint a_offset, const uint b_offset, const uint ib32, const uint i, const uint num_blocks_per_row, const uint first_row, const uint num_rows) {
+void calc_superblock(const uint a_offset, const uint b_offset, const uint ib32, const uint i,
+                               const uint num_blocks_per_row, const uint first_row, const uint num_rows) {
+    // Compute starting index in matrix B for this superblock
     const uint y_idx = i * QUANT_K + 32 * ib32;
-
     uint ibi = a_offset / QUANT_K + first_row * num_blocks_per_row + i;
+
+    // Precompute indices for quantization lookup tables
+    const uint qh_base = 2 * ib32;
+    const uint qs_base = 4 * ib32;
+    const uint sc_index = ib32 / 2;
+    const uint sc_shift = 6 * (ib32 & 1);
+
+    // Loop over rows in the superblock
     [[unroll]] for (uint n = 0; n < num_rows; ++n) {
+        // Load per-block scales and shift for quantization
         const uint16_t[4] scales = data_a[ibi].scales;
         const u16vec4 s = u16vec4(scales[0], scales[1], scales[2], scales[3]) >> 12;
         const float d = float(unpackHalf2x16(s.x | (s.y << 4) | (s.z << 8) | (s.w << 12)).x);
+        const uint sc = data_a[ibi].scales[sc_index] >> sc_shift;
 
-        const uint sc = data_a[ibi].scales[ib32 / 2] >> (6 * (ib32 & 1));
+        // Temporary caches for decoding
+        FLOAT_TYPE dl_cache[4];
+        uint16_t gvf_cache[4];
+        float delta_cache[4];
+
+        // Precompute the multiplier and lookup values for 4 sub-blocks
         [[unroll]] for (uint l = 0; l < 4; ++l) {
-            const uint qh = data_a[ibi].qh[2 * ib32 + l / 2] >> (4 * (l&1));
-            const uint qs = data_a[ibi].qs[4 * ib32 + l];
-            const float delta = ((qh & 8) != 0) ? -IQ1M_DELTA : IQ1M_DELTA;
-            const float dl = d * (2 * bitfieldExtract(sc, 3 * int(l / 2), 3) + 1);
-
-            const int16_t grid = int16_t(iq1s_grid[qs | ((qh & 7) << 8)]);
-
-            [[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 = FLOAT_TYPE(0.0);
-                [[unroll]] for (int k = 0; k < 4; ++k) {
-                    sum = fma(FLOAT_TYPE(b0[k]), bitfieldExtract(grid, 2 * k, 2) + delta,
-                          fma(FLOAT_TYPE(b4[k]), bitfieldExtract(grid, 8 + 2 * k, 2) + delta, sum));
-                }
-                temp[j][n] = fma(dl, sum, temp[j][n]);
+            dl_cache[l] = FLOAT_TYPE(d * (2 * bitfieldExtract(sc, 3 * int(l / 2), 3) + 1));
+            const uint qh = data_a[ibi].qh[qh_base + l / 2] >> (4 * (l & 1));
+            const uint qs = data_a[ibi].qs[qs_base + l];
+            gvf_cache[l] = iq1s_grid[qs | ((qh & 7) << 8)];
+            delta_cache[l] = ((qh & 8) != 0) ? -IQ1M_DELTA : IQ1M_DELTA;
+        }
+
+        // Loop over columns of the output
+        [[unroll]] for (uint j = 0; j < NUM_COLS; ++j) {
+            // Compute base index for matrix B
+            const uint base_b_idx = (j * p.batch_stride_b + b_offset + y_idx) / 4;
+            vec4 b_vals[8];
+
+            // Load 8 vec4 values from matrix B
+            [[unroll]] for (int idx = 0; idx < 8; ++idx) {
+                b_vals[idx] = vec4(data_b_v4[base_b_idx + idx]);
+            }
+
+            FLOAT_TYPE col_sum = FLOAT_TYPE(0.0);
+
+            // Loop over sub-blocks
+            [[unroll]] for (uint l = 0; l < 4; ++l) {
+                const uint16_t grid = gvf_cache[l];
+                const float dl = dl_cache[l];
+
+                // Decode 8 2-bit fbits from gvf_cache
+                float f0 = float(bitfieldExtract(grid, 0, 2));
+                float f1 = float(bitfieldExtract(grid, 2, 2));
+                float f2 = float(bitfieldExtract(grid, 4, 2));
+                float f3 = float(bitfieldExtract(grid, 6, 2));
+                float f4 = float(bitfieldExtract(grid, 8, 2));
+                float f5 = float(bitfieldExtract(grid, 10, 2));
+                float f6 = float(bitfieldExtract(grid, 12, 2));
+                float f7 = float(bitfieldExtract(grid, 14, 2));
+
+                // Pack into vec4 for vectorized FMA
+                const vec4 fbits_v0 = vec4(f0, f1, f2, f3);
+                const vec4 fbits_v1 = vec4(f4, f5, f6, f7);
+                const vec4 delta_v = vec4(delta_cache[l]);
+
+                // Vectorized fused multiply-add
+                vec4 sum_v = fma(b_vals[2*l + 0], fbits_v0 + delta_v, vec4(0.0));
+                sum_v      = fma(b_vals[2*l + 1], fbits_v1 + delta_v, sum_v);
+
+                // Horizontal add to get scalar sum
+                FLOAT_TYPE sum = sum_v.x + sum_v.y + sum_v.z + sum_v.w;
+
+                // Accumulate to column sum
+                col_sum = fma(dl, sum, col_sum);
             }
+            // Write result to temporary buffer
+            temp[j][n] += col_sum;
         }
         ibi += num_blocks_per_row;
     }