65eaca35dd
* Refactor where results of compilation are stored This commit refactors the internals of compilation in Wasmtime to change where results of individual function compilation are stored. Previously compilation resulted in many maps being returned, and compilation results generally held all these maps together. This commit instead switches this to have all metadata stored in a `CompiledFunction` instead of having a separate map for each item that can be stored. The motivation for this is primarily to help out with future module-linking-related PRs. What exactly "module level" is depends on how we interpret modules and how many modules are in play, so it's a bit easier for operations in wasmtime to work at the function level where possible. This means that we don't have to pass around multiple different maps and a function index, but instead just one map or just one entry representing a compiled function. Additionally this change updates where the parallelism of compilation happens, pushing it into `wasmtime-jit` instead of `wasmtime-environ`. This is another goal where `wasmtime-jit` will have more knowledge about module-level pieces with module linking in play. User-facing-wise this should be the same in terms of parallel compilation, though. The ultimate goal of this refactoring is to make it easier for the results of compilation to actually be a set of wasm modules. This means we won't be able to have a map-per-metadata where the primary key is the function index, because there will be many modules within one "object file". * Don't clear out fields, just don't store them Persist a smaller set of fields in `CompilationArtifacts` instead of trying to clear fields out and dynamically not accessing them.
This crate contains array-based data structures used by the core Cranelift code generator which use densely numbered entity references as mapping keys.
One major difference between this crate and crates like slotmap, slab, and generational-arena is that this crate currently provides no way to delete entities. This limits its use to situations where deleting isn't important, however this also makes it more efficient, because it doesn't need extra bookkeeping state to reuse the storage for deleted objects, or to ensure that new objects always have unique keys (eg. slotmap's and generational-arena's versioning).
Another major difference is that this crate protects against using a key from
one map to access an element in another. Where SlotMap, Slab, and Arena
have a value type parameter, PrimaryMap has a key type parameter and a value
type parameter. The crate also provides the entity_impl macro which makes it
easy to declare new unique types for use as keys. Any attempt to use a key in
a map it's not intended for is diagnosed with a type error.
Another is that this crate has two core map types, PrimaryMap and
SecondaryMap, which serve complementary purposes. A PrimaryMap creates its
own keys when elements are inserted, while an SecondaryMap reuses the keys
values of a PrimaryMap, conceptually storing additional data in the same
index space. SecondaryMap's values must implement Default and all elements
in an SecondaryMap initially have the value of default().
A common way to implement Default is to wrap a type in Option, however
this crate also provides the PackedOption utility which can use less memory
in some cases.
Additional utilities provided by this crate include:
EntityList, for allocating many small arrays (such as instruction operand lists in a compiler code generator).SparseMap: an alternative toSecondaryMapwhich can use less memory in some situations.EntitySet: a specialized form ofSecondaryMapusing a bitvector to record which entities are members of the set.