Lime is a series of defined and stable subsets of WebAssembly features that producers and consumers can both use to promote interoperability. It is intended to be implemented by producers such as LLVM, using features such as LLVM's concept of target CPUs. Once a Lime configuration is defined, it will be stable and not add or remove any features.
Lime configuration names include a version number, such as "Lime1". When there is a need to add or remove features, a new Lime configuration with a new version number will be defined, such as "Lime2".
Lime aims for features which do not involve significant new runtime cost or complexity, and can be implemented in mobile devices and other highly constrained environments.
The name "Lime" was inspired by abbreviating Linear Memory, as this series currently lacks wasm-gc and is therefore focused on linear-memory languages or language implementations.
The following Lime configurations have been defined:
The Lime1 target consists of WebAssembly 1.0 plus the following standardized (phase-5) features:
- mutable-globals
- multivalue
- sign-ext
- nontrapping-fptoint
- bulk-memory-opt
- extended-const
- call-indirect-overlong
WebAssembly features sometimes contain several features combined into a single proposal to simplify the standardization process, but can have very different implementation considerations. This section defines subsets of standardized features for use in Lime configurations.
bulk-memory-opt is a subset of the bulk-memory feature that contains just the
memory.copy and memory.fill instructions.
It does not include the table instructions, memory.init, or data.drop.
call-indirect-overlong is a subset of the reference-types feature that contains
just the change to the call_indirect instruction encoding to change the zero
byte to an LEB encoding which may have an overlong encoding.
It does not include the actual reference types.