Eliding the namespace when a container type has no decls was an
experiment in saving memory, but it ended up causing more trouble than
it was worth in various places. So, take the small memory hit for
reified types, and just give every container type a namespace.
The type `Zcu.Decl` in the compiler is problematic: over time it has
gained many responsibilities. Every source declaration, container type,
generic instantiation, and `@extern` has a `Decl`. The functions of
these `Decl`s are in some cases entirely disjoint.
After careful analysis, I determined that the two main responsibilities
of `Decl` are as follows:
* A `Decl` acts as the "subject" of semantic analysis at comptime. A
single unit of analysis is either a runtime function body, or a
`Decl`. It registers incremental dependencies, tracks analysis errors,
etc.
* A `Decl` acts as a "global variable": a pointer to it is consistent,
and it may be lowered to a specific symbol by the codegen backend.
This commit eliminates `Decl` and introduces new types to model these
responsibilities: `Cau` (Comptime Analysis Unit) and `Nav` (Named
Addressable Value).
Every source declaration, and every container type requiring resolution
(so *not* including `opaque`), has a `Cau`. For a source declaration,
this `Cau` performs the resolution of its value. (When #131 is
implemented, it is unsolved whether type and value resolution will share
a `Cau` or have two distinct `Cau`s.) For a type, this `Cau` is the
context in which type resolution occurs.
Every non-`comptime` source declaration, every generic instantiation,
and every distinct `extern` has a `Nav`. These are sent to codegen/link:
the backends by definition do not care about `Cau`s.
This commit has some minor technically-breaking changes surrounding
`usingnamespace`. I don't think they'll impact anyone, since the changes
are fixes around semantics which were previously inconsistent (the
behavior changed depending on hashmap iteration order!).
Aside from that, this changeset has no significant user-facing changes.
Instead, it is an internal refactor which makes it easier to correctly
model the responsibilities of different objects, particularly regarding
incremental compilation. The performance impact should be negligible,
but I will take measurements before merging this work into `master`.
Co-authored-by: Jacob Young <jacobly0@users.noreply.github.com>
Co-authored-by: Jakub Konka <kubkon@jakubkonka.com>
This allows the mutate mutex to only be locked during actual grows,
which are rare. For the lists that didn't previously have a mutex, this
change has little effect since grows are rare and there is zero
contention on a mutex that is only ever locked by one thread. This
change allows `extra` to be mutated without racing with a grow.
The purpose of using path digest was to reference a file in a
serializable manner. Now that there is a stable index associated with
files, it is a superior way to accomplish that goal, since removes one
layer of indirection, and makes TrackedInst 8 bytes instead of 20.
The saved Zig Compiler State file for "hello world" goes from 1.3M to
1.2M with this change.
Primarily, this commit removes 2 fields from File, relying on the data
being stored in the `files` field, with the key as the path digest, and
the value as the struct decl corresponding to the File. This table is
serialized into the compiler state that survives between incremental
updates.
Meanwhile, the File struct remains ephemeral data that can be
reconstructed the first time it is needed by the compiler process, as
well as operated on by independent worker threads.
A key outcome of this commit is that there is now a stable index that
can be used to refer to a File. This will be needed when serializing
error messages to survive incremental compilation updates.
This is essentially just a rename. I also changed the representation of
`AnalSubject` to use a `packed struct` rather than a non-exhaustive
enum, but that change is relatively trivial.
This patch is a pure rename plus only changing the file path in
`@import` sites, so it is expected to not create version control
conflicts, even when rebasing.
`LazySrcLoc` now stores a reference to the "base AST node" to which it
is relative. The previous tagged union is `LazySrcLoc.Offset`. To make
working with this structure convenient, `Sema.Block` contains a
convenience `src` method which takes an `Offset` and returns a
`LazySrcLoc`.
The "base node" of a source location is no longer given by a `Decl`, but
rather a `TrackedInst` representing either a `declaration`,
`struct_decl`, `union_decl`, `enum_decl`, or `opaque_decl`. This is a
more appropriate model, and removes an unnecessary responsibility from
`Decl` in preparation for the upcoming refactor which will split it into
`Nav` and `Cau`.
As a part of these `Decl` reworks, the `src_node` field is eliminated.
This change aids incremental compilation, and simplifies `Decl`. In some
cases -- particularly in backends -- the source location of a
declaration is desired. This was previously `Decl.srcLoc` and worked for
any `Decl`. Now, it is `Decl.navSrcLoc` in reference to the upcoming
refactor, since the set of `Decl`s this works for precisely corresponds
to what will in future become a `Nav` -- that is, source-level
declarations and generic function instantiations, but *not* type owner
Decls.
This commit introduces more tags to `LazySrcLoc.Offset` so as to
eliminate the concept of `error.NeededSourceLocation`. Now, `.unneeded`
should only be used to assert that an error path is unreachable. In the
future, uses of `.unneeded` can probably be replaced with `undefined`.
The `src_decl` field of `Sema.Block` no longer has a role in type
resolution. Its main remaining purpose is to handle namespacing of type
names. It will be eliminated entirely in a future commit to remove
another undue responsibility from `Decl`.
It is worth noting that in future, the `Zcu.SrcLoc` type should probably
be eliminated entirely in favour of storing `Zcu.LazySrcLoc` values.
This is because `Zcu.SrcLoc` is not valid across incremental updates,
and we want to be able to reuse error messages from previous updates
even if the source file in question changed. The error reporting logic
should instead simply resolve the location from the `LazySrcLoc` on the
fly.
This is in preparation for some upcoming changes to how we represent
source locations in the compiler. The bulk of the change here is dealing
with the removal of `src()` methods from `Zir` types.
This was a "fake" type used to handle C varargs parameters, much like
generic poison. In fact, it is treated identically to generic poison in
all cases other than one (the final coercion of a call argument), which
is trivially special-cased. Thus, it makes sense to remove this special
tag and instead use `generic_poison_type` in its place. This fixes
several bugs in Sema related to missing handling of this tag.
Resolves: #19781
We've got a big one here! This commit reworks how we represent pointers
in the InternPool, and rewrites the logic for loading and storing from
them at comptime.
Firstly, the pointer representation. Previously, pointers were
represented in a highly structured manner: pointers to fields, array
elements, etc, were explicitly represented. This works well for simple
cases, but is quite difficult to handle in the cases of unusual
reinterpretations, pointer casts, offsets, etc. Therefore, pointers are
now represented in a more "flat" manner. For types without well-defined
layouts -- such as comptime-only types, automatic-layout aggregates, and
so on -- we still use this "hierarchical" structure. However, for types
with well-defined layouts, we use a byte offset associated with the
pointer. This allows the comptime pointer access logic to deal with
reinterpreted pointers far more gracefully, because the "base address"
of a pointer -- for instance a `field` -- is a single value which
pointer accesses cannot exceed since the parent has undefined layout.
This strategy is also more useful to most backends -- see the updated
logic in `codegen.zig` and `codegen/llvm.zig`. For backends which do
prefer a chain of field and elements accesses for lowering pointer
values, such as SPIR-V, there is a helpful function in `Value` which
creates a strategy to derive a pointer value using ideally only field
and element accesses. This is actually more correct than the previous
logic, since it correctly handles pointer casts which, after the dust
has settled, end up referring exactly to an aggregate field or array
element.
In terms of the pointer access code, it has been rewritten from the
ground up. The old logic had become rather a mess of special cases being
added whenever bugs were hit, and was still riddled with bugs. The new
logic was written to handle the "difficult" cases correctly, the most
notable of which is restructuring of a comptime-only array (for
instance, converting a `[3][2]comptime_int` to a `[2][3]comptime_int`.
Currently, the logic for loading and storing work somewhat differently,
but a future change will likely improve the loading logic to bring it
more in line with the store strategy. As far as I can tell, the rewrite
has fixed all bugs exposed by #19414.
As a part of this, the comptime bitcast logic has also been rewritten.
Previously, bitcasts simply worked by serializing the entire value into
an in-memory buffer, then deserializing it. This strategy has two key
weaknesses: pointers, and undefined values. Representations of these
values at comptime cannot be easily serialized/deserialized whilst
preserving data, which means many bitcasts would become runtime-known if
pointers were involved, or would turn `undefined` values into `0xAA`.
The new logic works by "flattening" the datastructure to be cast into a
sequence of bit-packed atomic values, and then "unflattening" it; using
serialization when necessary, but with special handling for `undefined`
values and for pointers which align in virtual memory. The resulting
code is definitely slower -- more on this later -- but it is correct.
The pointer access and bitcast logic required some helper functions and
types which are not generally useful elsewhere, so I opted to split them
into separate files `Sema/comptime_ptr_access.zig` and
`Sema/bitcast.zig`, with simple re-exports in `Sema.zig` for their small
public APIs.
Whilst working on this branch, I caught various unrelated bugs with
transitive Sema errors, and with the handling of `undefined` values.
These bugs have been fixed, and corresponding behavior test added.
In terms of performance, I do anticipate that this commit will regress
performance somewhat, because the new pointer access and bitcast logic
is necessarily more complex. I have not yet taken performance
measurements, but will do shortly, and post the results in this PR. If
the performance regression is severe, I will do work to to optimize the
new logic before merge.
Resolves: #19452Resolves: #19460
`{}` for decls
`{p}` for enum fields
`{p_}` for struct fields and in contexts following a `.`
Elsewhere, `{p}` was used since it's equivalent to the old behavior.
