Implements the accepted proposal to introduce `@branchHint`. This
builtin is permitted as the first statement of a block if that block is
the direct body of any of the following:
* a function (*not* a `test`)
* either branch of an `if`
* the RHS of a `catch` or `orelse`
* a `switch` prong
* an `or` or `and` expression
It lowers to the ZIR instruction `extended(branch_hint(...))`. When Sema
encounters this instruction, it sets `sema.branch_hint` appropriately,
and `zirCondBr` etc are expected to reset this value as necessary. The
state is on `Sema` rather than `Block` to make it automatically
propagate up non-conditional blocks without special handling. If
`@panic` is reached, the branch hint is set to `.cold` if none was
already set; similarly, error branches get a hint of `.unlikely` if no
hint is explicitly provided. If a condition is comptime-known, `cold`
hints from the taken branch are allowed to propagate up, but other hints
are discarded. This is because a `likely`/`unlikely` hint just indicates
the direction this branch is likely to go, which is redundant
information when the branch is known at comptime; but `cold` hints
indicate that control flow is unlikely to ever reach this branch,
meaning if the branch is always taken from its parent, then the parent
is also unlikely to ever be reached.
This branch information is stored in AIR `cond_br` and `switch_br`. In
addition, `try` and `try_ptr` instructions have variants `try_cold` and
`try_ptr_cold` which indicate that the error case is cold (rather than
just unlikely); this is reachable through e.g. `errdefer unreachable` or
`errdefer @panic("")`.
A new API `unwrapSwitch` is introduced to `Air` to make it more
convenient to access `switch_br` instructions. In time, I plan to update
all AIR instructions to be accessed via an `unwrap` method which returns
a convenient tagged union a la `InternPool.indexToKey`.
The LLVM backend lowers branch hints for conditional branches and
switches as follows:
* If any branch is marked `unpredictable`, the instruction is marked
`!unpredictable`.
* Any branch which is marked as `cold` gets a
`llvm.assume(i1 true) [ "cold"() ]` call to mark the code path cold.
* If any branch is marked `likely` or `unlikely`, branch weight metadata
is attached with `!prof`. Likely branches get a weight of 2000, and
unlikely branches a weight of 1. In `switch` statements, un-annotated
branches get a weight of 1000 as a "middle ground" hint, since there
could be likely *and* unlikely *and* un-annotated branches.
For functions, a `cold` hint corresponds to the `cold` function
attribute, and other hints are currently ignored -- as far as I can tell
LLVM doesn't really have a way to lower them. (Ideally, we would want
the branch hint given in the function to propagate to call sites.)
The compiler and standard library do not yet use this new builtin.
Resolves: #21148
My main gripes with this design were that it was incorrectly namespaced, the naming was inconsistent and a bit wrong (`fooAlign` vs `fooAlignment`).
This commit moves all the logic from `PerThread.zig` to use the zcu + tid system that the previous couple commits introduce.
I've organized and merged the functions to be a bit more specific to their own purpose.
- `fieldAlignment` takes a struct or union type, an index, and a Zcu (or the Sema version which takes a Pt), and gives you the alignment of the field at the index.
- `structFieldAlignment` takes the field type itself, and provides the logic to handle special cases, such as externs.
A design goal I had in mind was to avoid using the word 'struct' in the function name, when it worked for things that aren't structs, such as unions.
I don't recall why I put these checks here -- they aren't correct. We
can freely recreate a type even if its fields have changed, because we
are going to re-do all type resolution.
The only conditions for recreations are (a) the ZIR index must not be
lost and (b) the number of captures must be the same. These conditions
are permissible because if either is violated, we can guarantee that
analysis of a valid `zirStructDecl` (etc) will never reference this
type (since the ZIR index has just been tracked, and the captures have
just been created based on the ZIR).
Adds a corresponding test case.
Resolves: #21185
This replaces the constant `Zir.Inst.Ref` tags (and the analagous tags
in `Air.Inst.Ref`, `InternPool.Index`) referring to types in
`std.builtin` with a ZIR instruction `extended(builtin_type(...))` which
instructs Sema to fetch such a type, effectively as if it were a
shorthand for the ZIR for `@import("std").builtin.xyz`.
Previously, this was achieved through constant tags in `Ref`. The
analagous `InternPool` indices began as `simple_type` values, and were
later rewritten to the correct type information. This system was kind of
brittle, and more importantly, isn't compatible with incremental
compilation of std, since incremental compilation relies on the ability
to recreate types at different indices when they change. Replacing the
old system with this instruction slightly increases the size of ZIR, but
it simplifies logic and allows incremental compilation to work correctly
on the standard library.
This shouldn't have a significant impact on ZIR size or compiler
performance, but I will take measurements in the PR to confirm this.
Without this, incremental updates which would change inferred error sets
fail, since they assume the IES is resolved and equals the old set,
resulting in false positive compile errors when e.g. coercing to an IES.
Another big commit, sorry! This commit makes all fixes necessary for
incremental updates of the compiler itself (specifically, adding a
breakpoint to `zirCompileLog`) to succeed, at least on the frontend.
The biggest change here is a reform to how types are handled. It works
like this:
* When a type is first created in `zirStructDecl` etc, its namespace is
scanned. If the type requires resolution, an `interned` dependency is
declared for the containing `AnalUnit`.
* `zirThis` also declared an `interned` dependency for its `AnalUnit` on
the namespace's owner type.
* If the type's namespace changes, the surrounding source declaration
changes hash, so `zirStructDecl` etc will be hit again. We check
whether the namespace has been scanned this generation, and re-scan it
if not.
* Namespace lookups also check whether the namespace in question
requires a re-scan based on the generation. This is because there's no
guarantee that the `zirStructDecl` is re-analyzed before the namespace
lookup is re-analyzed.
* If a type's structure (essentially its fields) change, then the type's
`Cau` is considered outdated. When the type is re-analyzed due to
being outdated, or the `zirStructDecl` is re-analyzed by being
transitively outdated, or a corresponding `zirThis` is re-analyzed by
being transitively outdated, the struct type is recreated at a new
`InternPool` index. The namespace's owner is updated (but not
re-scanned, since that is handled by the mechanisms above), and the
old type, while remaining a valid `Index`, is removed from the map
metadata so it will never be found by lookups. `zirStructDecl` and
`zirThis` store an `interned` dependency on the *new* type.
When a type becomes outdated, there will still be lingering references
to the old index -- for instance, any declaration whose value was that
type holds a reference to that index. These references may live for an
arbitrarily long time in some cases. So, we can't just remove the type
from the pool -- the old `Index` must remain valid!
Instead, we want to preserve the old `Index`, but avoid it from ever
appearing in lookups. (It's okay if analysis of something referencing
the old `Index` does weird stuff -- such analysis are guaranteed by the
incremental compilation model to always be unreferenced.) So, we use the
new `InternPool.putKeyReplace` to replace the shard entry for this index
with the newly-created index.
This commit makes more progress towards incremental compilation, fixing
some crashes in the frontend. Notably, it fixes the regressions introduced
by #20964. It also cleans up the "outdated file root" mechanism, by
virtue of deleting it: we now detect outdated file roots just after
updating ZIR refs, and re-scan their namespaces.
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 eliminates the statically-reachable recursion loop between code
generation backends and Sema. This is beneficial for optimizers
(although I do not measure any performance improvement for this change),
and for profilers.
Remove --debug-incremental
This flag is also added to the build system. Importantly, this tells
Compile step whether or not to keep the compiler running between
rebuilds. It defaults off because it is currently crashing
zirUpdateRefs.
Changes the `make` function signature to take an options struct, which
additionally includes `watch: bool`. I intentionally am not exposing
this information to configure phase logic.
Also adds global zig cache to the compiler cache prefixes.
Closes#20600
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.
