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Introduce perma-unstable `wasm-c-abi` flag
Now that `wasm-bindgen` v0.2.88 supports the spec-compliant C ABI, the idea is to switch to that in a future version of Rust. In the meantime it would be good to let people test and play around with it.
This PR introduces a new perma-unstable `-Zwasm-c-abi` compiler flag, which switches to the new spec-compliant C ABI when targeting `wasm32-unknown-unknown`.
Alternatively, we could also stabilize this and then deprecate it when we switch. I will leave this to the Rust maintainers to decide.
This is a companion PR to #117918, but they could be merged independently.
MCP: https://github.com/rust-lang/compiler-team/issues/703
Tracking issue: https://github.com/rust-lang/rust/issues/122532
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We want to run them on all 64-bit platforms.
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The actual ABI implication here is that in some cases the values
are required to be "consecutive", i.e. must either all be passed
in registers or all on stack (without padding).
Adjust the code to either use Uniform::new() or Uniform::consecutive()
depending on which behavior is needed.
Then, when lowering this in LLVM, skip the [1 x i128] to i128
simplification if is_consecutive is set. i128 is the only case
I'm aware of where this is problematic right now. If we find
other cases, we can extend this (either based on target information
or possibly just by not simplifying for is_consecutive entirely).
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When passing a 16 (or higher) aligned struct by value on ppc64le,
it needs to be passed as an array of `i128` rather than an array
of `i64`. This will force the use of an even starting register.
For the case of a 16 byte struct with alignment 16 it is important
that `[1 x i128]` is used instead of `i128` -- apparently, the
latter will get treated similarly to `[2 x i64]`, not exhibiting
the correct ABI. Add a `force_array` flag to `Uniform` to support
this.
The relevant clang code can be found here:
https://github.com/llvm/llvm-project/blob/fe2119a7b08b6e468b2a67768904ea85b1bf0a45/clang/lib/CodeGen/Targets/PPC.cpp#L878-L884
https://github.com/llvm/llvm-project/blob/fe2119a7b08b6e468b2a67768904ea85b1bf0a45/clang/lib/CodeGen/Targets/PPC.cpp#L780-L784
I think the corresponding psABI wording is this:
> Fixed size aggregates and unions passed by value are mapped to as
> many doublewords of the parameter save area as the value uses in
> memory. Aggregrates and unions are aligned according to their
> alignment requirements. This may result in doublewords being
> skipped for alignment.
In particular the last sentence.
Fixes https://github.com/rust-lang/rust/issues/122767.
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Check `x86_64` size assertions on `aarch64`, too
(Context: https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Checking.20size.20assertions.20on.20aarch64.3F)
Currently the compiler has around 30 sets of `static_assert_size!` for various size-critical data structures (e.g. various IR nodes), guarded by `#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]`.
(Presumably this cfg avoids having to maintain separate size values for 32-bit targets and unusual 64-bit targets. Apparently it may have been necessary before the i128/u128 alignment changes, too.)
This is slightly incovenient for people on aarch64 workstations (e.g. Macs), because the assertions normally aren't checked until we push to a PR. So this PR adds `aarch64` to the `#[cfg(..)]` guarding all of those assertions in the compiler.
---
Implemented with a simple find/replace. Verified by manually inspecting each `static_assert_size!` in `compiler/`, and checking that either the replacement succeeded, or adding aarch64 wouldn't have been appropriate.
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This makes it easier for contributors on aarch64 workstations (e.g. Macs) to
notice when these assertions have been violated.
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This reverts commit 41c6fa812b0bed63e54c455134734452f9cee97c.
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special case that's not present in Clang
Making the methods consistent doesn't require much justification. It's
required for us to generate correct code.
The special case was present near the end of `CastTarget::llvm_type`, and
resulted in the final integer component of the ABI type being shrunk to
the smallest integer that fits.
You can see this in action here (https://godbolt.org/z/Pe73cr91d),
where, for a struct with 5 u16 elements, rustc generates
`{ i64, i16 }`, while Clang generates `[2 x i64]`.
This special case was added a long time ago, when the function was
originally written [1]. That commit consolidated logic from many
backends, and in some of the code it deleted, sparc64 [2] and
powerpc64 [3] had similar special cases.
However, looking at Clang today, it doesn't have this special case for
sparc64 (https://godbolt.org/z/YaafvYWdf) or powerpc64
(https://godbolt.org/z/5c3YePTje), so this change just removes it.
[1]: https://github.com/rust-lang/rust/commit/f0636b61c7f84962a609e831760db9d77f4f5e14#diff-183c4dadf10704bd1f521b71f71d89bf755c9603a93f894d66c03bb1effc6021R231
[2]: https://github.com/rust-lang/rust/commit/f0636b61c7f84962a609e831760db9d77f4f5e14#diff-2d8f87ea6db6d7f0a6fbeb1d5549adc07e93331278d951a1e051a40f92914436L163-L166
[3]: https://github.com/rust-lang/rust/commit/f0636b61c7f84962a609e831760db9d77f4f5e14#diff-88af4a9df9ead503a5c7774a0455d270dea3ba60e9b0ec1ce550b4c53d3bce3bL172-L175
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This would trigger a `Size::sub: 0 - 8 would result in negative size` abort,
if `data.last_offset > offset`.
This is almost hilariously easy to trigger (https://godbolt.org/z/8rbv57xET):
```rust
#[repr(C)]
pub struct DoubleFloat {
f: f64,
g: f32,
}
#[no_mangle]
pub extern "C" fn foo(x: DoubleFloat) {}
```
Tests for this will be covered by the cast-target-abi.rs test added in a later commit.
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Stop using LLVM struct types for byval/sret
For `byval` and `sret`, the type has no semantic meaning, only the size matters\*†. Using `[N x i8]` is a more direct way to specify that we want `N` bytes, and avoids relying on LLVM's struct layout.
\*: The alignment would matter, if we didn't explicitly specify it. From what I can tell, we always specified the alignment for `sret`; for `byval`, we didn't until #112157.
†: For `byval`, the hidden copy may be impacted by padding in the LLVM struct type, i.e. padding bytes may not be copied. (I'm not sure if this is done today, but I think it would be legal.) But we manually pad our LLVM struct types specifically to avoid there ever being LLVM-visible padding, so that shouldn't be an issue.
Split out from #121577.
r? `@nikic`
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Co-authored-by: Ralf Jung <post@ralfj.de>
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Introduces the `arm64ec-pc-windows-msvc` target for building Arm64EC ("Emulation Compatible") binaries for Windows.
For more information about Arm64EC see <https://learn.microsoft.com/en-us/windows/arm/arm64ec>.
Tier 3 policy:
> A tier 3 target must have a designated developer or developers (the "target maintainers") on record to be CCed when issues arise regarding the target. (The mechanism to track and CC such developers may evolve over time.)
I will be the maintainer for this target.
> Targets must use naming consistent with any existing targets; for instance, a target for the same CPU or OS as an existing Rust target should use the same name for that CPU or OS. Targets should normally use the same names and naming conventions as used elsewhere in the broader ecosystem beyond Rust (such as in other toolchains), unless they have a very good reason to diverge. Changing the name of a target can be highly disruptive, especially once the target reaches a higher tier, so getting the name right is important even for a tier 3 target.
Target uses the `arm64ec` architecture to match LLVM and MSVC, and the `-pc-windows-msvc` suffix to indicate that it targets Windows via the MSVC environment.
> Target names should not introduce undue confusion or ambiguity unless absolutely necessary to maintain ecosystem compatibility. For example, if the name of the target makes people extremely likely to form incorrect beliefs about what it targets, the name should be changed or augmented to disambiguate it.
Target name exactly specifies the type of code that will be produced.
> If possible, use only letters, numbers, dashes and underscores for the name. Periods (.) are known to cause issues in Cargo.
Done.
> Tier 3 targets may have unusual requirements to build or use, but must not create legal issues or impose onerous legal terms for the Rust project or for Rust developers or users.
> The target must not introduce license incompatibilities.
Uses the same dependencies, requirements and licensing as the other `*-pc-windows-msvc` targets.
> Anything added to the Rust repository must be under the standard Rust license (MIT OR Apache-2.0).
Understood.
> The target must not cause the Rust tools or libraries built for any other host (even when supporting cross-compilation to the target) to depend on any new dependency less permissive than the Rust licensing policy. This applies whether the dependency is a Rust crate that would require adding new license exceptions (as specified by the tidy tool in the rust-lang/rust repository), or whether the dependency is a native library or binary. In other words, the introduction of the target must not cause a user installing or running a version of Rust or the Rust tools to be subject to any new license requirements.
> Compiling, linking, and emitting functional binaries, libraries, or other code for the target (whether hosted on the target itself or cross-compiling from another target) must not depend on proprietary (non-FOSS) libraries. Host tools built for the target itself may depend on the ordinary runtime libraries supplied by the platform and commonly used by other applications built for the target, but those libraries must not be required for code generation for the target; cross-compilation to the target must not require such libraries at all. For instance, rustc built for the target may depend on a common proprietary C runtime library or console output library, but must not depend on a proprietary code generation library or code optimization library. Rust's license permits such combinations, but the Rust project has no interest in maintaining such combinations within the scope of Rust itself, even at tier 3.
> "onerous" here is an intentionally subjective term. At a minimum, "onerous" legal/licensing terms include but are not limited to: non-disclosure requirements, non-compete requirements, contributor license agreements (CLAs) or equivalent, "non-commercial"/"research-only"/etc terms, requirements conditional on the employer or employment of any particular Rust developers, revocable terms, any requirements that create liability for the Rust project or its developers or users, or any requirements that adversely affect the livelihood or prospects of the Rust project or its developers or users.
Uses the same dependencies, requirements and licensing as the other `*-pc-windows-msvc` targets.
> Neither this policy nor any decisions made regarding targets shall create any binding agreement or estoppel by any party. If any member of an approving Rust team serves as one of the maintainers of a target, or has any legal or employment requirement (explicit or implicit) that might affect their decisions regarding a target, they must recuse themselves from any approval decisions regarding the target's tier status, though they may otherwise participate in discussions.
> This requirement does not prevent part or all of this policy from being cited in an explicit contract or work agreement (e.g. to implement or maintain support for a target). This requirement exists to ensure that a developer or team responsible for reviewing and approving a target does not face any legal threats or obligations that would prevent them from freely exercising their judgment in such approval, even if such judgment involves subjective matters or goes beyond the letter of these requirements.
Understood, I am not a member of the Rust team.
> Tier 3 targets should attempt to implement as much of the standard libraries as possible and appropriate (core for most targets, alloc for targets that can support dynamic memory allocation, std for targets with an operating system or equivalent layer of system-provided functionality), but may leave some code unimplemented (either unavailable or stubbed out as appropriate), whether because the target makes it impossible to implement or challenging to implement. The authors of pull requests are not obligated to avoid calling any portions of the standard library on the basis of a tier 3 target not implementing those portions.
Both `core` and `alloc` are supported.
Support for `std` dependends on making changes to the standard library, `stdarch` and `backtrace` which cannot be done yet as the bootstrapping compiler raises a warning ("unexpected `cfg` condition value") for `target_arch = "arm64ec"`.
> The target must provide documentation for the Rust community explaining how to build for the target, using cross-compilation if possible. If the target supports running binaries, or running tests (even if they do not pass), the documentation must explain how to run such binaries or tests for the target, using emulation if possible or dedicated hardware if necessary.
Documentation is provided in src/doc/rustc/src/platform-support/arm64ec-pc-windows-msvc.md
> Tier 3 targets must not impose burden on the authors of pull requests, or other developers in the community, to maintain the target. In particular, do not post comments (automated or manual) on a PR that derail or suggest a block on the PR based on a tier 3 target. Do not send automated messages or notifications (via any medium, including via @) to a PR author or others involved with a PR regarding a tier 3 target, unless they have opted into such messages.
> Backlinks such as those generated by the issue/PR tracker when linking to an issue or PR are not considered a violation of this policy, within reason. However, such messages (even on a separate repository) must not generate notifications to anyone involved with a PR who has not requested such notifications.
> Patches adding or updating tier 3 targets must not break any existing tier 2 or tier 1 target, and must not knowingly break another tier 3 target without approval of either the compiler team or the maintainers of the other tier 3 target.
> In particular, this may come up when working on closely related targets, such as variations of the same architecture with different features. Avoid introducing unconditional uses of features that another variation of the target may not have; use conditional compilation or runtime detection, as appropriate, to let each target run code supported by that target.
Understood.
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Make changes necessary to support these types in the compiler.
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Varargs support for system ABI
This PR allows functions with the `system` ABI to be variadic (under the `extended_varargs_abi_support` feature tracked in #100189). On x86 windows, the `system` ABI is equivalent to `C` for variadic functions. On other platforms, `system` is already equivalent to `C`.
Fixes #110505
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This involves lots of breaking changes. There are two big changes that
force changes. The first is that the bitflag types now don't
automatically implement normal derive traits, so we need to derive them
manually.
Additionally, bitflags now have a hidden inner type by default, which
breaks our custom derives. The bitflags docs recommend using the impl
form in these cases, which I did.
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the unadjusted ABI needs to pass aggregates by-value
Fixes https://github.com/rust-lang/rust/issues/118124, a regression introduced in https://github.com/rust-lang/rust/pull/117500
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Similar to the previous commit, this replaces `newtype_index`'s opt-out
`no_ord_impl` attribute with the opt-in `orderable` attribute.
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By default, `newtype_index!` types get a default `Encodable`/`Decodable`
impl. You can opt out of this with `custom_encodable`. Opting out is the
opposite to how Rust normally works with autogenerated (derived) impls.
This commit inverts the behaviour, replacing `custom_encodable` with
`encodable` which opts into the default `Encodable`/`Decodable` impl.
Only 23 of the 59 `newtype_index!` occurrences need `encodable`.
Even better, there were eight crates with a dependency on
`rustc_serialize` just from unused default `Encodable`/`Decodable`
impls. This commit removes that dependency from those eight crates.
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Ensure sanity of all computed ABIs
This moves the ABI sanity assertions from the codegen backend to the ABI computation logic. Sadly, due to past mistakes, we [have to](https://github.com/rust-lang/rust/pull/117351#issuecomment-1788495503) be able to compute a sane ABI for nonsensical function types like `extern "C" fn(str) -> str`. So to make the sanity check pass we first need to make all ABI adjustment deal with unsized types... and we have no shared infrastructure for those adjustments, so that's a bunch of copy-paste. At least we have assertions failing loudly when one accidentally sets a different mode for an unsized argument.
To achieve this, this re-lands the parts of https://github.com/rust-lang/rust/pull/80594 that got reverted in https://github.com/rust-lang/rust/pull/81388. To avoid breaking wasm ABI again, that ABI now explicitly opts-in to the (wrong, broken) ABI that we currently keep for backwards compatibility. That's still better than having *every* ABI use the wrong broken default!
Cc `@bjorn3`
Fixes https://github.com/rust-lang/rust/issues/115845
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Remove asmjs
Fulfills [MCP 668](https://github.com/rust-lang/compiler-team/issues/668).
`asmjs-unknown-emscripten` does not work as-specified, and lacks essential upstream support for generating asm.js, so it should not exist at all.
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non-ZST member
This ensures that `MaybeUninit<T>` has the same ABI as `T` when passed
through an `extern "C"` function.
Fixes https://github.com/rust-lang/rust/issues/115509
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member
This ensures that `MaybeUninit<T>` has the same ABI as `T` when passed
through an `extern "C"` function.
Fixes https://github.com/rust-lang/rust/issues/115481.
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improve PassMode docs
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into helper function
like is_bool, and some special magic extra fields
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