This avoids the set uniqueness (hashing) test, reduces memory
churn when re-mapping virtual register onto real registers, and is
generally more memory-efficient.
It isn't used by anything except for the C API and all of our embedder-exposed
APIs are already internally `Rc`-based, so it doesn't make sense to use with
them.
If you aren't expecting `VMExternRef`'s pointer-equality semantics, then these
trait implementations can be foot guns. Instead of implementing the trait, make
free functions in the `VMExternRef` namespace. This way, callers have to be a
little more explicit.
This is enough to get an `externref -> externref` identity function
passing.
However, `externref`s that are dropped by compiled Wasm code are (safely)
leaked. Follow up work will leverage cranelift's stack maps to resolve this
issue.
In the `ModuleEnvironment::declare_signature` callback, also pass the original
Wasm function signature, so that consumers may associate this information with
each compiled function. This is often necessary because while each Wasm
signature gets compiled down into a single native signature, multiple Wasm
signatures might compile down into the same native signature, and in these cases
the original Wasm signature is required for dynamic type checking of calls.
`VMExternRef` is a reference-counted box for any kind of data that is
external and opaque to running Wasm. Sometimes it might hold a Wasmtime
thing, other times it might hold something from a Wasmtime embedder and is
opaque even to us. It is morally equivalent to `Rc<dyn Any>` in Rust, but
additionally always fits in a pointer-sized word. `VMExternRef` is
non-nullable, but `Option<VMExternRef>` is a null pointer.
The one part of `VMExternRef` that can't ever be opaque to us is the
reference count. Even when we don't know what's inside an `VMExternRef`, we
need to be able to manipulate its reference count as we add and remove
references to it. And we need to do this from compiled Wasm code, so it must
be `repr(C)`!
`VMExternRef` itself is just a pointer to an `VMExternData`, which holds the
opaque, boxed value, its reference count, and its vtable pointer.
The `VMExternData` struct is *preceded* by the dynamically-sized value boxed
up and referenced by one or more `VMExternRef`s:
```ignore
,-------------------------------------------------------.
| |
V |
+----------------------------+-----------+-----------+ |
| dynamically-sized value... | ref_count | value_ptr |---'
+----------------------------+-----------+-----------+
| VMExternData |
+-----------------------+
^
+-------------+ |
| VMExternRef |-------------------+
+-------------+ |
|
+-------------+ |
| VMExternRef |-------------------+
+-------------+ |
|
... ===
|
+-------------+ |
| VMExternRef |-------------------'
+-------------+
```
The `value_ptr` member always points backwards to the start of the
dynamically-sized value (which is also the start of the heap allocation for
this value-and-`VMExternData` pair). Because it is a `dyn` pointer, it is
fat, and also points to the value's `Any` vtable.
The boxed value and the `VMExternRef` footer are held a single heap
allocation. The layout described above is used to make satisfying the
value's alignment easy: we just need to ensure that the heap allocation used
to hold everything satisfies its alignment. It also ensures that we don't
need a ton of excess padding between the `VMExternData` and the value for
values with large alignment.
About half of the `FuncEnvironment::translate_table_*` methods were using the
`TableIndex` newtype, while the other half were using raw `u32`s. This commit
makes everything use `TableIndex`.
# Overview
This commit makes changes to the `wiggle::from_witx` procedural in order
to allow for escaping strict and reserved Rust keywords.
Additionally, this commit introduces the ability to use a `witx_literal`
field in the `{..}` object provided as an argument to
`wiggle::from_witx`. This field allows for witx documents to be provided
as inline string literals.
Documentation comments are added to the methods of
`wiggle_generate::names::Names` struct responsible for generating
`proc_macro2::Ident` words.
## Keyword Escaping
Today, an interface that includes witx identifiers that conflict with
with Rust syntax will cause the `from_witx` macro to panic at
compilation time.
Here is a small example (adapted from
`/crates/wiggle/tests/keywords.rs`) that demonstrates this issue:
```
;; Attempts to define a module `self`, containing a trait `Self`. Both
;; of these are reserved keywords, and will thus cause a compilation
;; error.
(module $self
(@interface func (export "betchya_cant_implement_this")
)
)
```
Building off of code that (as of `master` today)
[demonstrates a strategy][esc] for escaping keywords, we introduce an
internal `escaping` module to `generate/src/config.rs` that contains
code responsible for escaping Rust keywords in a generalized manner.
[esc]: 0dd77d36f8/crates/wiggle/generate/src/names.rs (L106)
Some code related to special cases, such as accounting for
[`errno::2big`][err] while generating names for enum variants, is moved
into this module as well.
[err]: https://github.com/WebAssembly/WASI/blob/master/phases/snapshot/docs.md#-errno-enumu16
As mentioned in the document comments of this diff, we do not include
weak keywords like `'static` or `union`. Their semantics do not impact
us in the same way from a code generation perspective.
## witx_literal
First, some background. Trait names, type names, and so on use a
camel-cased naming convention. As such, `Self` is the only keyword that
can potentially conflict with these identifiers. (See the [Rust
Reference][key] for a complete list of strict, reserved, and weak
keywords.)
When writing tests, this meant that many tests had to be outlined into
separate files, as items with the name `$self` could not be defined in
the same namespace. As such, it seemed like a worthwhile feature to
implement while the above work was being developed.
The most important function to note is the `load_document` inherent
method added to `WitxConf`, and that `WitxConf` is now an enum
containing either (a) a collection of paths, identical to its current
functionality, or (b) a single string literal.
Note that a witx document given to `from_witx` using a string literal
provided to `from_witx` cannot include `use (..)` directives, per
the `witx::parse` documentation.
(See: https://docs.rs/witx/0.8.5/witx/fn.parse.html)
Two newtypes, `Paths` and `Literal`, are introduced to facilitate the
parsing of `WitxConf` values. Their public API and trait implementations
has been kept to the minimum required to satisfy compilation in order to
limit the scope of this diff. Additional surface for external consumers
can be added in follow-up commits if deemed necessary in review.
The InsertLane format has an ordering (`value().imm().value()`) and immediate name (`"lane"`) that make it awkward to use for other instructions. This changes the ordering (`value().value().imm()`) and uses the default name (`"imm"`) throughout the codebase.
* Encode vselect using BLEND instructions on x86
* Legalize vselect to bitselect
* Optimize bitselect to vselect for some operands
* Add run tests for bitselect-vselect optimization
* Address review feedback
* Ensure GlobalSet on vectors are cast to Cranelift's I8X16 type
This is a fix related to the decision to use Cranelift's I8X16 type to represent Wasm's V128--it requires casting to maintain type correctness. See https://github.com/bytecodealliance/wasmtime/issues/1147.
* Enable SIMD spec test: simd_lane.wast
* Add documentation for building programs using AssemblyScript.
* Add the assemblyscript hello world as an example and display it inline.
* Move the AssemblyScript hello world into the docs directory.
That way Cargo doesn't try to run it like a Rust example.
* Minor code tidying.
* Document that `Linker::iter`'s iteration order is arbitrary.
* Add a few more tests for `wasmtime::Linker`.
* Refactor `Linker::compute_imports`.
- Extract the error message generation into a separate function.
- In the error message, sort the candidates.
* Fix a typo in a comment.
* Add `__rtti_base` to the list of allowed but deprecated exports.
* Don't print an Error message when a program exits normally.
* Update comments to reflect the current code.
* Also allow "table" as an exported table, which is used by AssemblyScript.
I'm not actually sure that it's possible to write `#[test]` in a
`proc-macro` crate. Regardless I don't think it's too too conventional,
so let's disable this for now.
Closes#1775
Benjamin Bouvier
teapotd
Nick Fitzgerald
Pat Hickey
Pat Hickey
Katelyn Martin
Andrew Brown
Alex Crichton
Leonardo Yvens
whitequark
Dan Gohman