2.1 KiB
Minimal Build
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Configuration
In order to compile a minimal build - i.e. a build optimized for size - perhaps for no-std embedded targets or for
compiling to [WASM], it is essential that the correct linker flags are used in cargo.toml:
[profile.release]
lto = "fat" # turn on Link-Time Optimizations
codegen-units = 1 # trade compile time with maximum optimization
opt-level = "z" # optimize for size
Use i32 Only
For embedded systems that must optimize for code size, the architecture is commonly 32-bit.
Use [only_i32] to prune away large sections of code implementing functions for other numeric types
(including i64).
If, for some reason, 64-bit long integers must be supported, use [only_i64] instead of [only_i32].
Opt-Out of Features
Opt out of as many features as possible, if they are not needed, to reduce code size because, remember, by default all code is compiled in as what a script requires cannot be predicted. If a language feature is not needed, omitting them via special features is a prudent strategy to optimize the build for size.
Omitting arrays ([no_index]) yields the most code-size savings, followed by floating-point support
([no_float]), checked arithmetic/script resource limits ([unchecked]) and finally object maps and custom types ([no_object]).
Where the usage scenario does not call for loading externally-defined modules, use [no_module] to save some bytes.
Disable script-defined functions ([no_function]) when the feature is not needed.
Both of these have little code size savings.
Use a Raw [Engine]
Engine::new_raw creates a raw engine.
A raw engine supports, out of the box, only a very restricted set
of basic arithmetic and logical operators.
Selectively include other necessary functionalities by loading specific [packages] to minimize the footprint.
Packages are sharable (even across threads via the [sync] feature), so they only have to be created once.