Change History#

Since the original release 1.0 of the WebAssembly specification, a number of proposals for extensions have been integrated. The following sections provide an overview of what has changed.

Release 2.0#

Sign extension instructions#

Added new numeric instructions for performing sign extension within integer representations [1].

  • New numeric instructions: \(\mathsf{i}\mathit{nn}\mathsf{.}\href{../syntax/instructions.html#syntax-instr-numeric}{\mathsf{extend}}\mathit{N}\mathsf{\_s}\)

Non-trapping float-to-int conversions#

Added new conversion instructions that avoid trapping when converting a floating-point number to an integer [2].

  • New numeric instructions: \(\mathsf{i}\mathit{nn}\mathsf{.}\href{../syntax/instructions.html#syntax-instr-numeric}{\mathsf{trunc}}\mathsf{\_sat\_f}\mathit{mm}\mathsf{\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\)

Multiple values#

Generalized the result type of blocks and functions to allow for multiple values; in addition, introduced the ability to have block parameters [3].

Reference types#

Added \(\href{../syntax/types.html#syntax-reftype}{\mathsf{funcref}}\) and \(\href{../syntax/types.html#syntax-reftype}{\mathsf{externref}}\) as new value types and respective instructions [4].

  • New value types: reference types \(\href{../syntax/types.html#syntax-reftype}{\mathsf{funcref}}\) and \(\href{../syntax/types.html#syntax-reftype}{\mathsf{externref}}\)

  • New reference instructions: \(\href{../syntax/instructions.html#syntax-instr-ref}{\mathsf{ref{.}null}}\), \(\href{../syntax/instructions.html#syntax-instr-ref}{\mathsf{ref{.}func}}\), \(\href{../syntax/instructions.html#syntax-instr-ref}{\mathsf{ref{.}is\_null}}\)

  • Enrich parametric instruction: \(\href{../syntax/instructions.html#syntax-instr-parametric}{\mathsf{select}}\) with optional type immediate

  • New declarative form of element segment

Table instructions#

Added instructions to directly access and modify tables [4].

  • Table types allow any reference type as element type

  • New table instructions: \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.get}}\), \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.set}}\), \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.size}}\), \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.grow}}\)

Multiple tables#

Added the ability to use multiple tables per module [4].

  • Modules may define, import, and export multiple tables

  • Table instructions take a table index immediate: \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.get}}\), \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.set}}\), \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.size}}\), \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.grow}}\), \(\href{../syntax/instructions.html#syntax-instr-control}{\mathsf{call\_indirect}}\)

  • Element segments take a table index

Bulk memory and table instructions#

Added instructions that modify ranges of memory or table entries [4] [5]

  • New memory instructions: \(\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{memory.fill}}\), \(\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{memory.init}}\), \(\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{memory.copy}}\), \(\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{data.drop}}\)

  • New table instructions: \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.fill}}\), \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.init}}\), \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{table.copy}}\), \(\href{../syntax/instructions.html#syntax-instr-table}{\mathsf{elem.drop}}\)

  • New passive form of data segment

  • New passive form of element segment

  • New data count section in binary format

  • Active data and element segments boundaries are no longer checked at compile time but may trap instead

Vector instructions#

Added vector type and instructions that manipulate multiple numeric values in parallel (also known as SIMD, single instruction multiple data) [6]

  • New value type: \(\href{../syntax/types.html#syntax-valtype}{\mathsf{v128}}\)

  • New memory instructions: \(\mathsf{v128.}\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{load}}\), \(\mathsf{v128.}\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{load}}{}\!N\!\mathsf{x}\!M\!\mathsf{\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{v128.}\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{load}}{}N\mathsf{\_zero}\), \(\mathsf{v128.}\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{load}}{}N\mathsf{\_splat}\), \(\mathsf{v128.}\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{load}}{}N\mathsf{\_lane}\), \(\mathsf{v128.}\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{store}}\), \(\mathsf{v128.}\href{../syntax/instructions.html#syntax-instr-memory}{\mathsf{store}}{}N\mathsf{\_lane}\)

  • New constant vector instruction: \(\mathsf{v128.}\href{../syntax/instructions.html#syntax-instr-vec}{\mathsf{const}}\)

  • New unary vector instructions: \(\mathsf{v128.not}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.abs}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.neg}\), \(\mathsf{i8x16.popcnt}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.abs}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.neg}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.sqrt}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.ceil}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.floor}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.trunc}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.nearest}\)

  • New binary vector instructions: \(\mathsf{v128.and}\), \(\mathsf{v128.andnot}\), \(\mathsf{v128.or}\), \(\mathsf{v128.xor}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.add}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.sub}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.mul}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.add\_sat\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.sub\_sat\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.min\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.max\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.shl}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.shr\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.add}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.extmul\_}\href{../syntax/instructions.html#syntax-half}{\mathit{half}}\mathsf{\_i}\!N'\!\mathsf{x}\!M'\!\mathsf{\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i16x8.q15mulr\_sat\_s}\), \(\mathsf{i32x4.dot\_i16x8\_s}\), \(\mathsf{i16x8.extadd\_pairwise\_i8x16\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i32x4.extadd\_pairwise\_i16x8\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i8x16.avgr\_u}\), \(\mathsf{i16x8.avgr\_u}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.sub}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.mul}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.div}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.min}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.max}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.pmin}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.pmax}\)

  • New ternary vector instruction: \(\mathsf{v128.bitselect}\)

  • New test vector instructions: \(\mathsf{v128.any\_true}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.all\_true}\)

  • New relational vector instructions: \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.eq}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.ne}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.lt\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.gt\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.le\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.ge\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.eq}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.ne}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.lt}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.gt}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.le}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.ge}\)

  • New conversion vector instructions:\(\mathsf{i32x4.trunc\_sat\_f32x4\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i32x4.trunc\_sat\_f64x2\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\mathsf{\_zero}\), \(\mathsf{f32x4.convert\_i32x4\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{f32x4.demote\_f64x2\_zero}\), \(\mathsf{f64x2.convert\_low\_i32x4\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{f64x2.promote\_low\_f32x4}\)

  • New lane access vector instructions: \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.extract\_lane\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}^?\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.replace\_lane}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.extract\_lane}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.replace\_lane}\)

  • New lane splitting/combining vector instructions: \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.extend\_}\href{../syntax/instructions.html#syntax-half}{\mathit{half}}\mathsf{\_i}\!N'\!\mathsf{x}\!M'\!\mathsf{\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i8x16.narrow\_i16x8\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\), \(\mathsf{i16x8.narrow\_i32x4\_}\href{../syntax/instructions.html#syntax-sx}{\mathit{sx}}\)

  • New byte reordering vector instructions: \(\mathsf{i8x16.shuffle}\), \(\mathsf{i8x16.swizzle}\)

  • New injection/projection vector instructions: \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.splat}\), \(\mathsf{f}\!N\!\mathsf{x}\!M\!\mathsf{.splat}\), \(\mathsf{i}\!N\!\mathsf{x}\!M\!\mathsf{.bitmask}\)