ggml-webgpu: Add fused RMS_NORM + MUL (#21983)

* fused rms_norm_mul + mul

* Add GGML_WEBGPU_DISABLE_FUSION for being able to disable kernel fusion.

* Decouple num_fused_ops from webgpu_context; misc cleanup

* Fix eps handling and remove disable_fusion.

* Fix not to use c++20 initializers.

ggml/src/ggml-webgpu/ggml-webgpu-shader-lib.hpp

@@ -194,6 +194,26 @@ struct ggml_webgpu_row_norm_pipeline_key_hash {
     }
 };
 
+/** RMS_NORM + MUL **/
+
+struct ggml_webgpu_rms_norm_mul_pipeline_key {
+    bool inplace;
+    bool src_overlap;
+
+    bool operator==(const ggml_webgpu_rms_norm_mul_pipeline_key & other) const {
+        return inplace == other.inplace && src_overlap == other.src_overlap;
+    }
+};
+
+struct ggml_webgpu_rms_norm_mul_pipeline_key_hash {
+    size_t operator()(const ggml_webgpu_rms_norm_mul_pipeline_key & key) const {
+        size_t seed = 0;
+        ggml_webgpu_hash_combine(seed, key.inplace);
+        ggml_webgpu_hash_combine(seed, key.src_overlap);
+        return seed;
+    }
+};
+
 /** Pad **/
 struct ggml_webgpu_pad_pipeline_key {
     bool circular;
@@ -517,7 +537,7 @@ inline uint32_t ggml_webgpu_flash_attn_max_kv_tile(const ggml_webgpu_shader_lib_
     const size_t q_tile       = context.sg_mat_m;
     const size_t base_q_bytes = (key.head_dim_qk + key.head_dim_v) * q_tile * GGML_WEBGPU_F16_SIZE_BYTES +
                                 2 * q_tile * GGML_WEBGPU_F32_SIZE_BYTES;
-    size_t bytes_per_kv = 0;
+    size_t       bytes_per_kv = 0;
     if (!key.kv_direct) {
         bytes_per_kv += std::max(key.head_dim_qk, key.head_dim_v);
     }
@@ -755,16 +775,17 @@ class ggml_webgpu_shader_lib {
     std::unordered_map<int, webgpu_pipeline> cumsum_pipelines;         // key is fixed, no variants yet
     std::unordered_map<ggml_webgpu_row_norm_pipeline_key, webgpu_pipeline, ggml_webgpu_row_norm_pipeline_key_hash>
         row_norm_pipelines;                                            // op/inplace
+
     std::unordered_map<ggml_webgpu_get_rows_pipeline_key, webgpu_pipeline, ggml_webgpu_get_rows_pipeline_key_hash>
-        get_rows_pipelines;                                            // src_type, vectorized
+        get_rows_pipelines;   // src_type, vectorized
     std::unordered_map<ggml_webgpu_unary_pipeline_key, webgpu_pipeline, ggml_webgpu_unary_pipeline_key_hash>
-        unary_pipelines;                                               // type/op/inplace
+        unary_pipelines;      // type/op/inplace
     std::unordered_map<ggml_webgpu_scale_pipeline_key, webgpu_pipeline, ggml_webgpu_scale_pipeline_key_hash>
-        scale_pipelines;                                               // inplace
+        scale_pipelines;      // inplace
     std::unordered_map<ggml_webgpu_solve_tri_pipeline_key, webgpu_pipeline, ggml_webgpu_solve_tri_pipeline_key_hash>
-        solve_tri_pipelines;                                           // type
+        solve_tri_pipelines;  // type
     std::unordered_map<ggml_webgpu_ssm_conv_pipeline_key, webgpu_pipeline, ggml_webgpu_ssm_conv_pipeline_key_hash>
-        ssm_conv_pipelines;                                            // type/vectorized
+        ssm_conv_pipelines;   // type/vectorized
     std::unordered_map<ggml_webgpu_gated_delta_net_pipeline_key,
                        webgpu_pipeline,
                        ggml_webgpu_gated_delta_net_pipeline_key_hash>
@@ -813,6 +834,11 @@ class ggml_webgpu_shader_lib {
     std::unordered_map<ggml_webgpu_conv2d_pipeline_key, webgpu_pipeline, ggml_webgpu_conv2d_pipeline_key_hash>
         conv2d_pipelines;
 
+    std::unordered_map<ggml_webgpu_rms_norm_mul_pipeline_key,
+                       webgpu_pipeline,
+                       ggml_webgpu_rms_norm_mul_pipeline_key_hash>
+        rms_norm_mul_pipelines;
+
   public:
     ggml_webgpu_shader_lib(wgpu::Device device) { this->device = device; }
 
@@ -1828,6 +1854,39 @@ class ggml_webgpu_shader_lib {
         return unary_pipelines[key];
     }
 
+    webgpu_pipeline get_rms_norm_mul_pipeline(const ggml_webgpu_shader_lib_context & context) {
+        ggml_webgpu_rms_norm_mul_pipeline_key key = {};
+        key.inplace                               = context.inplace;
+        key.src_overlap                           = context.src_overlap;
+
+        auto it = rms_norm_mul_pipelines.find(key);
+        if (it != rms_norm_mul_pipelines.end()) {
+            return it->second;
+        }
+
+        std::vector<std::string> defines;
+        std::string              op_name = "RMS_NORM_MUL";
+        std::string              variant = op_name;
+
+        if (key.inplace) {
+            defines.push_back("INPLACE");
+            variant += "_inplace";
+        } else if (key.src_overlap) {
+            defines.push_back("SRC_OVERLAP");
+            variant += "_src_overlap";
+        }
+
+        defines.push_back(std::string("WG_SIZE=") + std::to_string(context.max_wg_size));
+
+        auto processed              = preprocessor.preprocess(wgsl_rms_norm_mul, defines);
+        auto decisions              = std::make_shared<ggml_webgpu_generic_shader_decisions>();
+        decisions->wg_size          = context.max_wg_size;
+        webgpu_pipeline pipeline    = ggml_webgpu_create_pipeline(device, processed, variant);
+        pipeline.context            = decisions;
+        rms_norm_mul_pipelines[key] = pipeline;
+        return rms_norm_mul_pipelines[key];
+    }
+
     webgpu_pipeline get_binary_pipeline(const ggml_webgpu_shader_lib_context & context) {
         ggml_webgpu_binary_pipeline_key key = {};
         key.type                            = context.dst->type;