77ab99d3b0
* Cleanups to cranelift-frontend SSA construction * Encode sealed/undef_variables relationship in type A block can't have any undef_variables if it is sealed. It's useful to make that fact explicit in the types so that any time either value is used, it's clear that we should think about the other one too. In addition, encoding this fact in an enum type lets Rust apply an optimization that reduces the size of SSABlockData by 8 bytes, making it fit in a 64-byte cache line. I haven't taken the extra step of making SSABlockData be 64-byte aligned because 1) it doesn't seem to have a performance impact and b) doing so makes other structures quite a bit bigger. * Simplify finish_predecessors_lookup Using Vec::drain is more concise than a combination of iter().rev().take() followed by Vec::truncate. And in this case it doesn't matter what order we examine the results in, because we just want to know if they're all equal, so we might as well iterate forward instead of in reverse. There's no need for the ZeroOneOrMore enum. Instead, there are only two cases: either we have a single value to use for the variable (possibly synthesized as a constant zero), or we need to add a block parameter in every predecessor. Pre-filtering the results iterator to eliminate the sentinel makes it easy to identify how many distinct definitions this variable has. iter.next() indicates if there are any definitions at all, and then iter.all() is a clear way to express that we want to know if the remaining definitions are the same as the first one. * Simplify append_jump_argument * Avoid assigning default() into SecondaryMap This eliminates some redundant reads and writes. * cranelift-frontend: Construct with default() This eliminates a bunch of boilerplate in favor of a built in `derive` macro. Also I'm deleting an import that had the comment "FIXME: Remove in edition2021", which we've been using everywhere since April. * Fix tests
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.