## 4 Tools for WebAssembly Development
### WebAssembly Standardized Features for Existing Web Browsers and Tools
Bulk Memory Operations (BMO) were introduced in response to observations that functions such as _memcpy_ and _memset_ are frequently used and can significantly impact performance in Wasm benchmarks. This proposal aims to provide more efficient memory copying and filling operations. A prototype implementation of the _memory.copy_ instruction was created, comparing it to an existing implementation generated by emscripten. The benchmark tests the performance of copying size bytes of data from one address to another without overlapping, and repeats this process \(N\) times. The results show potential for significant performance improvements with optimized bulk memory operations. Conditional Segment Initialization (CSI) is motivated by the need to share Wasm modules among multiple agents. Under the current threading proposal, if a module is shared, it needs to be instantiated multiple times, potentially resulting in multiple initializations of linear memory and overwriting of stores. CSI introduces the concept of passive segments that are not automatically copied into memory or tables during instantiation. Instead, they require manual application using the new _memory.init_ and _table.init_ instructions. By distinguishing between active and passive segments, finer control over memory initialization is achieved, ensuring proper sharing of modules without data corruption. The design of BMO involves new instructions such as _memory.copy_, _table.copy_, and _memory.fill_. These instructions enable efficient copying and filling of memory regions and tables. The binary format for the data section includes segments with a memory index, an initializer expression for offset, and raw data. The proposal repurposes the memory index field to serve as a flags field, allowing for additional meanings attached to nonzero values. Passive segments, indicated by the low bit of the flags field, are not automatically copied on instantiation, and require manual application using _memory.init_ and _table.init_ instructions. Segments can be shrunk to size zero using the data.drop and elem.drop instructions. As with passive segments, active segments have an implicit initialization and drop process as part of the module's start function. Furthermore, the reference-types proposal introduces the notion of function references, and allows element segments to be used for forward-declaring functions with addresses that will be taken. The proposal introduces the bulk instructions _table.fill_ and _table.grow_, which take a function reference as an initializer argument. The validation process and initialization behavior are updated with the bulk memory scheme. Active segments are initialized in module-definition order, with out-of-bounds checks to prevent instantiation failures. Data that have already been written for previous in-bounds segments remain unchanged. Instructions such as _memory.init_, _data.drop_, _memory.copy_, _memory.fill_, _table.init_, _elem.drop_, and _table.copy_ enable efficient segment initialization, copying, and filling operations in Wasm. The parameters and signatures of these instructions determine the source and destination addresses, offsets, and sizes, ensuring that bounds checks are performed to prevent memory access violations. The introduction of the _DataCount_ section addresses the issue of _memory.init_ and _data.drop_ instructions breaking the guarantee of single-pass validation. This new section provides information about the number of data segments defined in the Data section, enabling proper validation during the parsing of the Code section. Overall, these proposals enhance the memory management capabilities of Wasm, allowing for more efficient memory operations, controlled initialization of segments, and optimized sharing of modules among multiple agents. * **Extended Constant Expressions** This approach aims to expand the capabilities of constant expressions in Wasm. The current specification for constant expressions is limited, and was always intended to be extended.