remove explicit deref of AbiAlign for most methods
Much of the compiler calls functions on Align projected from AbiAlign. AbiAlign impls Deref to its inner Align, so we can simplify these away. Also, it will minimize disruption when AbiAlign is removed.
For now, preserve usages that might resolve to PartialOrd or PartialEq, as those have odd inference.
Much of the compiler calls functions on Align projected from AbiAlign.
AbiAlign impls Deref to its inner Align, so we can simplify these away.
Also, it will minimize disruption when AbiAlign is removed.
For now, preserve usages that might resolve to PartialOrd or PartialEq,
as those have odd inference.
We lost the following comment during refactorings:
The current code for niche-filling relies on variant indices instead of actual discriminants, so enums with explicit discriminants (RFC 2363) would misbehave.
In PR 90877 T-lang decided not to remove `intrinsics::pref_align_of`.
However, the intrinsic and its supporting code
1. is a nightly feature, so can be removed at compiler/libs discretion
2. requires considerable effort in the compiler to support, as it
necessarily complicates every single site reasoning about alignment
3. has been justified based on relevance to codegen, but it is only a
requirement for C++ (not C, not Rust) stack frame layout for AIX,
in ways Rust would not consider even with increased C++ interop
4. is only used by rustc to overalign some globals, not correctness
5. can be adequately replaced by other rules for globals, as it mostly
affects alignments for a few types under 16 bytes of alignment
6. has only one clear benefactor: automating C -> Rust translation
for GNU extensions like `__alignof`
7. such code was likely intended to be `alignof` or `_Alignof`,
because the GNU extension is a "false friend" of the C keyword,
which makes the choice to support such a mapping very questionable
8. makes it easy to do incorrect codegen in the compiler by its mere
presence as usual Rust rules of alignment (e.g. `size == align * N`)
do not hold with preferred alignment
The implementation is clearly damaging the code quality of the compiler.
Thus it is within the compiler team's purview to simply rip it out.
If T-lang wishes to have this intrinsic restored for c2rust's benefit,
it would have to use a radically different implementation that somehow
does not cause internal incorrectness.
Until then, remove the intrinsic and its supporting code, as one tool
and an ill-considered GCC extension cannot justify risking correctness.
Because we touch a fair amount of the compiler to change this at all,
and unfortunately the duplication of AbiAndPrefAlign is deep-rooted,
we keep an "AbiAlign" type which we can wean code off later.
This pair of fn was introduced to perform invariant checks for scalars.
Their current behavior doesn't mesh as well with checking SIMD types,
so change the name of the fn to reflect their actual use-case and
refactor the corresponding checks.
Also simplify the returns from Option<AbiAndPrefAlign> to Option<Align>,
because every site was mapping away the "preferred" alignment anyways.
previously field ordering was using the same seed for all instances of Foo,
now we pass seed values through the layout tree so that not only
the struct itself affects layout but also its fields
The initial naming of "Abi" was an awful mistake, conveying wrong ideas
about how psABIs worked and even more about what the enum meant.
It was only meant to represent the way the value would be described to
a codegen backend as it was lowered to that intermediate representation.
It was never meant to mean anything about the actual psABI handling!
The conflation is because LLVM typically will associate a certain form
with a certain ABI, but even that does not hold when the special cases
that actually exist arise, plus the IR annotations that modify the ABI.
Reframe `rustc_abi::Abi` as the `BackendRepr` of the type, and rename
`BackendRepr::Aggregate` as `BackendRepr::Memory`. Unfortunately, due to
the persistent misunderstandings, this too is now incorrect:
- Scattered ABI-relevant code is entangled with BackendRepr
- We do not always pre-compute a correct BackendRepr that reflects how
we "actually" want this value to be handled, so we leave the backend
interface to also inject various special-cases here
- In some cases `BackendRepr::Memory` is a "real" aggregate, but in
others it is in fact using memory, and in some cases it is a scalar!
Our rustc-to-backend lowering code handles this sort of thing right now.
That will eventually be addressed by lifting duplicated lowering code
to either rustc_codegen_ssa or rustc_target as appropriate.
Add `LayoutS::is_uninhabited` and use it
Use accessors for the things that accessors are good at: reducing everyone's need to be nosy and peek at the internals of every data structure.
For structs that cannot be unsized, the layout algorithm sometimes moves
unsized fields to the end of the struct, which circumvented the error
for unexpected unsized fields and returned an unsized layout anyway.
This commit makes it so that the unexpected unsized error is always
returned for structs that cannot be unsized, allowing us to remove an
old hack and fixing some old ICE.
Disable dead variant removal for `#[repr(C)]` enums.
This prevents removing dead branches from a `#[repr(C)]` enum (they now get discriminants allocated as if they were inhabited).
Implementation notes: ABI of something like
```rust
#[repr(C)]
enum Foo {
Foo(!),
}
```
is still `Uninhabited`, but its layout is now computed as if all the branches were inhabited.
This seemed to me like a proper way to do it, especially given that ABI sanity check explicitly asserts that type-level uninhabitedness implies ABI uninhabitedness.
This probably needs some sort of FCP (given that it changes `#[repr(C)]` layout, which is a stable guarantee), but I’m not sure how to call for one or which team is the most relevant.
See https://github.com/rust-lang/unsafe-code-guidelines/issues/500.
Represent `Result<usize, Box<T>>` as ScalarPair(i64, ptr)
This allows types like `Result<usize, std::io::Error>` (and integers of differing sign, e.g. `Result<u64, i64>`) to be passed in a pair of registers instead of through memory, like `Result<u64, u64>` or `Result<Box<T>, Box<U>>` are today.
Fixes#97540.
r? `@ghost`
From `impl Into<DiagnosticMessage>` to `impl Into<Cow<'static, str>>`.
Because these functions don't produce user-facing output and we don't
want their strings to be translated.
