[metal] extend bin op fusion to MUL/SUB/DIV chains (#28)

ggml/src/ggml-metal/ggml-metal-common.cpp

@@ -394,20 +394,30 @@ void ggml_graph_optimize(ggml_cgraph * gf) {
         // fuse only ops that start with these operations
         // can be expanded when needed
         if (node.op() == GGML_OP_ADD ||
+            node.op() == GGML_OP_SUB ||
+            node.op() == GGML_OP_MUL ||
+            node.op() == GGML_OP_DIV ||
             node.op() == GGML_OP_NORM ||
             node.op() == GGML_OP_RMS_NORM) {
             ops[0] = node.op();
 
             int f = i + 1;
             while (f < n && f < i + MAX_FUSE) {
-                // conservatively allow fusing only these ops
-                // can be expanded when needed
+                // bin ops (ADD/SUB/MUL/DIV) must be same type to fuse
+                // NORM/RMS_NORM can chain with MUL/ADD
+                if (node.op() == GGML_OP_ADD ||
+                    node.op() == GGML_OP_SUB ||
+                    node.op() == GGML_OP_MUL ||
+                    node.op() == GGML_OP_DIV) {
+                    if (gf->nodes[f]->op != node.op()) break;
+                } else {
                     if (gf->nodes[f]->op != GGML_OP_ADD &&
                         gf->nodes[f]->op != GGML_OP_MUL &&
                         gf->nodes[f]->op != GGML_OP_NORM &&
                         gf->nodes[f]->op != GGML_OP_RMS_NORM) {
                         break;
                     }
+                }
                 ops[f - i] = gf->nodes[f]->op;
                 f++;
             }

ggml/src/ggml-metal/ggml-metal-ops.cpp

@@ -3118,19 +3118,15 @@ int ggml_metal_op_bin(ggml_metal_op_t ctx, int idx) {
 
     int n_fuse = 1;
 
-    // c[0] = add(a,    b[0])
-    // c[1] = add(c[0], b[1])
-    // c[2] = add(c[1], b[2])
+    // c[0] = op(a,     b[0])
+    // c[1] = op(c[0],  b[1])
+    // c[2] = op(c[1],  b[2])
     // ...
     if (use_fusion) {
-        fops[0] = GGML_OP_ADD;
-        fops[1] = GGML_OP_ADD;
-        fops[2] = GGML_OP_ADD;
-        fops[3] = GGML_OP_ADD;
-        fops[4] = GGML_OP_ADD;
-        fops[5] = GGML_OP_ADD;
-        fops[6] = GGML_OP_ADD;
-        fops[7] = GGML_OP_ADD;
+        ggml_op cur_op = op->op;
+        for (int i = 0; i < 8; ++i) {
+            fops[i] = cur_op;
+        }
 
         // note: in metal, we sometimes encode the graph in parallel so we have to avoid fusing ops
         //       across splits. idx_end indicates the last node in the current split
@@ -3165,7 +3161,7 @@ int ggml_metal_op_bin(ggml_metal_op_t ctx, int idx) {
         ++n_fuse;
 
         if (debug_fusion > 1 && n_fuse > 1) {
-            GGML_LOG_DEBUG("%s: fuse: ADD x %d\n", __func__, n_fuse);
+            GGML_LOG_DEBUG("%s: fuse: %s x %d\n", __func__, ggml_op_name(cur_op), n_fuse);
         }
     }