This reverts commit a7de02e05216db9a04e438703ddf1b6b12f3fbef.
This did not implement the accepted proposal, and I did not sign off
on the changes. I would like a chance to review this, please.
Previously the error had a note suggesting to use `try`, `catch`, or
`if`, even for error sets where none of those work.
Instead, in case of an error set the way you can handle the error
depends very much on the specific case. For example you might be in a
`catch` where you are discarding or ignoring the error set capture
value, in which case one way to handle the error might be to `return`
the error.
So, in that case, we do not attach that error note.
Additionally, this makes the error tell you what kind of an error it is:
is it an error set or an error union? This distinction is very relevant
in how to handle the error.
Maybe I'm just being pedantic here (most likely) but I don't like how we're
just telling the user here how to "suppress this error" by "assigning the value to '_'".
I think it's better if we use the word "discard" here which I think is
the official terminology and also tells the user what it actually means
to "assign the value to '_'".
Also, using the value would also be a way to "suppress the error".
It is just one of the two options: discard or use.
the truncation panic logic is generated in Sema, so I don't need to roll anything
of my own. I add all of the boilerplate for that detecting the truncation and it works
in basic test cases!
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
Certain types (notably, `std.ComptimeStringMap`) were resulting in excessively
long type names when instantiated, which in turn resulted in excessively long
symbol names. These are problematic for two reasons:
* Symbol names are sometimes read by humans -- they ought to be readable.
* Some other applications (looking at you, xcode) trip on very long symbol names.
To work around this for now, we cap the depth of value printing at 1, as opposed
to the normal 3. This doesn't guarantee anything -- there could still be, for
instance, an incredibly long aggregate -- but it works around the issue in
practice for the time being.
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
There is no way to know the expected parent pointer attributes (most
notably alignment) from the type of the field pointer, so provide them
in the first argument.
Legacy anon decls now have three uses:
* Type owner decls
* Function owner decls
* `@export` and `@extern`
Therefore, there are no longer any cases where we wish to explicitly
omit legacy anon decls from the binary. This means we can remove the
concept of an "alive" vs "dead" `Decl`, which also allows us to remove
the separate `anon_work_queue` in `Compilation`.
This commit also performs some refactors to `TypedValue.print` in
preparation for improved comptime pointer access logic. Once that logic
exists, `TypedValue.print` can use Sema to access pointers for more
helpful printing.
This commit also implements proposal #19435, because the existing logic
there relied on some blatantly incorrect code in `Value.sliceLen`.
Resolves: #19435
Good riddance!
Most of these changes are trivial. There's a fix for a minor bug this
exposed in `Value.readFromPackedMemory`, but aside from that, it's all
just things like changing `intern` calls to `toIntern`.
Perhaps someday, we will make Sema operate on mutable values more
generally. For now, it makes sense to split out this representation,
since it is only used in comptime pointer accesses.
There are some currently unused methods on `MutableValue` which will
be used once I rewrite the comptime pointer access logic to be less
terrible.
The commit following this one will - at long last - delete the legacy
Value representation
`Decl` can no longer store un-interned values, so this field is now
unnecessary. The type can instead be fetched with the new `typeOf`
helper method, which just gets the type of the Decl's `Value`.
This commit changes how we represent comptime-mutable memory
(`comptime var`) in the compiler in order to implement the intended
behavior that references to such memory can only exist at comptime.
It does *not* clean up the representation of mutable values, improve the
representation of comptime-known pointers, or fix the many bugs in the
comptime pointer access code. These will be future enhancements.
Comptime memory lives for the duration of a single Sema, and is not
permitted to escape that one analysis, either by becoming runtime-known
or by becoming comptime-known to other analyses. These restrictions mean
that we can represent comptime allocations not via Decl, but with state
local to Sema - specifically, the new `Sema.comptime_allocs` field. All
comptime-mutable allocations, as well as any comptime-known const allocs
containing references to such memory, live in here. This allows for
relatively fast checking of whether a value references any
comptime-mtuable memory, since we need only traverse values up to
pointers: pointers to Decls can never reference comptime-mutable memory,
and pointers into `Sema.comptime_allocs` always do.
This change exposed some faulty pointer access logic in `Value.zig`.
I've fixed the important cases, but there are some TODOs I've put in
which are definitely possible to hit with sufficiently esoteric code. I
plan to resolve these by auditing all direct accesses to pointers (most
of them ought to use Sema to perform the pointer access!), but for now
this is sufficient for all realistic code and to get tests passing.
This change eliminates `Zcu.tmp_hack_arena`, instead using the Sema
arena for comptime memory mutations, which is possible since comptime
memory is now local to the current Sema.
This change should allow `Decl` to store only an `InternPool.Index`
rather than a full-blown `ty: Type, val: Value`. This commit does not
perform this refactor.
When the slice-by-length start position is runtime-known, it is likely
protected by a runtime-known condition and therefore a compile error is
less appropriate than a runtime panic check.
This is demonstrated in the json code that was updated and then reverted
in this commit.
When #3806 is implemented, this decision can be reassessed.
Revert "std: work around compiler unable to evaluate condition at compile time"
Revert "frontend: comptime array slice-by-length OOB detection"
This reverts commit 7741aca96c8cc6df7e8c4bd10ada741d6a3ffb9d.
This reverts commit 2583b389eaf5f7aaa0eb79b51126506c1e172d15.
