Sized Hierarchy: Part I
This patch implements the non-const parts of rust-lang/rfcs#3729. It introduces two new traits to the standard library, `MetaSized` and `PointeeSized`. See the RFC for the rationale behind these traits and to discuss whether this change makes sense in the abstract.
These traits are unstable (as is their constness), so users cannot refer to them without opting-in to `feature(sized_hierarchy)`. These traits are not behind `cfg`s as this would make implementation unfeasible, there would simply be too many `cfg`s required to add the necessary bounds everywhere. So, like `Sized`, these traits are automatically implemented by the compiler.
RFC 3729 describes changes which are necessary to preserve backwards compatibility given the introduction of these traits, which are implemented and as follows:
- `?Sized` is rewritten as `MetaSized`
- `MetaSized` is added as a default supertrait for all traits w/out an explicit sizedness supertrait already.
There are no edition migrations implemented in this, as these are primarily required for the constness parts of the RFC and prior to stabilisation of this (and so will come in follow-up PRs alongside the const parts). All diagnostic output should remain the same (showing `?Sized` even if the compiler sees `MetaSized`) unless the `sized_hierarchy` feature is enabled.
Due to the use of unstable extern types in the standard library and rustc, some bounds in both projects have had to be relaxed already - this is unfortunate but unavoidable so that these extern types can continue to be used where they were before. Performing these relaxations in the standard library and rustc are desirable longer-term anyway, but some bounds are not as relaxed as they ideally would be due to the inability to relax `Deref::Target` (this will be investigated separately).
It is hoped that this is implemented such that it could be merged and these traits could exist "under the hood" without that being observable to the user (other than in any performance impact this has on the compiler, etc). Some details might leak through due to the standard library relaxations, but this has not been observed in test output.
**Notes:**
- Any commits starting with "upstream:" can be ignored, as these correspond to other upstream PRs that this is based on which have yet to be merged.
- This best reviewed commit-by-commit. I've attempted to make the implementation easy to follow and keep similar changes and test output updates together.
- Each commit has a short description describing its purpose.
- This patch is large but it's primarily in the test suite.
- I've worked on the performance of this patch and a few optimisations are implemented so that the performance impact is neutral-to-minor.
- `PointeeSized` is a different name from the RFC just to make it more obvious that it is different from `std::ptr::Pointee` but all the names are yet to be bikeshed anyway.
- `@nikomatsakis` has confirmed [that this can proceed as an experiment from the t-lang side](https://rust-lang.zulipchat.com/#narrow/channel/435869-project-goals/topic/SVE.20and.20SME.20on.20AArch64.20.28goals.23270.29/near/506196491)
- FCP in https://github.com/rust-lang/rust/pull/137944#issuecomment-2912207485Fixesrust-lang/rust#79409.
r? `@ghost` (I'll discuss this with relevant teams to find a reviewer)
Set elf e_flags on ppc64 targets according to abi
(This PR contains the non user-facing changes of https://github.com/rust-lang/rust/pull/142321)
Fixes https://github.com/rust-lang/rust/issues/85589 by making sure that ld.lld errors out instead of generating a broken binary.
Basically the problem is that ld.lld assumes that all ppc64 object files with e_flags=0 are object files which use the ELFv2 ABI (this here is the check https://github.com/llvm/llvm-project/blob/main/lld/ELF/Arch/PPC64.cpp#L639).
This pull request sets the correct e_flags to indicate the used ABI so ld.lld errors out when encountering ELFv1 ABI files instead of generating a broken binary.
For example compare code generation for this program (file name ``min.rs``):
```rust
#![feature(no_core, lang_items, repr_simd)]
#![crate_type = "bin"]
#![no_core]
#![no_main]
#[lang = "sized"]
trait Sized {}
#[lang = "copy"]
trait Copy {}
#[lang = "panic_cannot_unwind"]
pub fn panic() -> ! {
loop {}
}
pub fn my_rad_unmangled_function() {
loop {}
}
pub fn my_rad_function() {
loop {}
}
#[no_mangle]
pub fn _start() {
my_rad_unmangled_function();
my_rad_function();
}
```
Compile with ``rustc --target=powerpc64-unknown-linux-gnu -C linker=ld.lld -C relocation-model=static min.rs``
Before change:
```
$ llvm-objdump -d min
Disassembly of section .text:
000000001001030c <.text>:
...
10010334: 7c 08 02 a6 mflr 0
10010338: f8 21 ff 91 stdu 1, -112(1)
1001033c: f8 01 00 80 std 0, 128(1)
10010340: 48 02 00 39 bl 0x10030378 <_ZN3min25my_rad_unmangled_function17h7471c49af58039f5E>
10010344: 60 00 00 00 nop
10010348: 48 02 00 49 bl 0x10030390 <_ZN3min15my_rad_function17h37112b8fd1008c9bE>
1001034c: 60 00 00 00 nop
...
```
The branch instructions ``bl 0x10030378`` and ``bl 0x10030390`` are jumping into the ``.opd`` section which is data. That is a broken binary (because fixing those branches is the task of the linker).
After change:
```
error: linking with `ld.lld` failed: exit status: 1
|
= note: "ld.lld" "/tmp/rustcNYKZCS/symbols.o" "<1 object files omitted>" "--as-needed" "-L" "/tmp/rustcNYKZCS/raw-dylibs" "-Bdynamic" "--eh-frame-hdr" "-z" "noexecstack" "-L" "<sysroot>/lib/rustlib/powerpc64-unknown-linux-gnu/lib" "-o" "min" "--gc-sections" "-z" "relro" "-z" "now"
= note: some arguments are omitted. use `--verbose` to show all linker arguments
= note: ld.lld: error: /tmp/rustcNYKZCS/symbols.o: ABI version 1 is not supported
```
Which is correct because ld.lld doesn't support ELFv1 ABI.
Revert overeager warning for misuse of `--print native-static-libs`
In a PR to emit warnings on misuse of `--print native-static-libs`, we did not consider the matter of composing parts of build systems. If you are not directly invoking rustc, it can be difficult to know when you will in fact compile a staticlib, so making sure uses `--print native-static-lib` correctly can be just a nuisance.
Next cycle we can reland a slightly more narrowly focused variant or one that focuses on `--emit` instead of `--print native-static-libs`. But in its current state, I am not sure the warning is very useful.
Make sure to propagate result from `visit_expr_fields`
We weren't propagating the `ControlFlow::Break` out of a struct field, which means that the solution implemented in rust-lang/rust#130443 didn't work for nested fields.
Fixesrust-lang/rust#142525.
Reject union default field values
Fixesrust-lang/rust#142555.
The [`default_field_values` RFC][rfc] does not specify that default field values may be used on `union`s, and it's not clear how default field values may be used with `union`s without an design extension to the RFC. So, for now, reject trying to use default field values with `union`s.
### Review notes
- The first commit adds the `union` with default field values test case to `tests/ui/structs/default-field-values/failures.rs`, where `union`s with default field values are currently accepted.
- The second commit rejects trying to supply default field values to `union` definitions.
- When `default_field_values` feature gate is disabled, we show the feature gate error when the user tries to write `union`s with default field values. When the feature gate is enabled, we reject this usage with
> unions cannot have default field values
``@rustbot`` label: +F-default_field_values
[rfc]: https://rust-lang.github.io/rfcs/3681-default-field-values.html
Manually invalidate caches in SimplifyCfg.
The current `SimplifyCfg` pass unconditionally invalidates CFG caches. This is unfortunate if there are no modifications that require this invalidation.
`nominal_obligations` calls `predicates_of` on a `Sized` obligation,
effectively elaborating the trait and making the well-formedness checking
machinery do a bunch of extra work checking a `MetaSized` obligation is
well-formed, but given that both `Sized` and `MetaSized` are built-ins,
if `Sized` is otherwise well-formed, so `MetaSized` will be.
As a performance optimization, skip elaborating the supertraits of
`Sized`, and if a `MetaSized` obligation is being checked, then look for
a `Sized` predicate in the parameter environment. This makes the
`ParamEnv` smaller which should improve compiler performance as it avoids
all the iteration over the larger `ParamEnv`.
When printing impl headers in a diagnostic, the compiler has to account
for `?Sized` implying `MetaSized` and new `MetaSized` and `PointeeSized`
bounds.
Like `Sized` diagnostics, sorting `MetaSized` and `PointeeSized`
diagnostics last prevents earlier more useful diagnostics from being
skipped because there has already been error tainting.
Given the necessary additions of bounds to these traits and their impls
in the standard library, it is necessary to add `MetaSized` bounds to
the obligation which is proven as part of checking for dyn
dispatchability.
Opting-out of `Sized` with `?Sized` is now equivalent to adding a
`MetaSized` bound, and adding a `MetaSized` or `PointeeSized` bound
is equivalent to removing the default `Sized` bound - this commit
implements this change in `rustc_hir_analysis::hir_ty_lowering`.
`MetaSized` is also added as a supertrait of all traits, as this is
necessary to preserve backwards compatibility.
Unfortunately, non-global where clauses being preferred over item bounds
(where `PointeeSized` bounds would be proven) - which can result in
errors when a `PointeeSized` supertrait/bound/predicate is added to some
items. Rather than `PointeeSized` being a bound on everything, it can
be the absence of a bound on everything, as `?Sized` was.
As core uses an extern type (`ptr::VTable`), the default `?Sized` to
`MetaSized` migration isn't sufficient, and some code that previously
accepted `VTable` needs relaxed to continue to accept extern types.
Similarly, the compiler uses many extern types in `rustc_codegen_llvm`
and in the `rustc_middle::ty::List` implementation (`OpaqueListContents`)
some bounds must be relaxed to continue to accept these types.
Unfortunately, due to the current inability to relax `Deref::Target`,
some of the bounds in the standard library are forced to be stricter than
they ideally would be.
In a PR to emit warnings on misuse of `--print native-static-libs`,
we did not consider the matter of composing parts of build systems.
If you are not directly invoking rustc, it can be difficult to know
when you will in fact compile a staticlib, so making sure everyone
uses `--print native-static-lib` correctly can be just a nuisance.
This reverts the following commits:
- f66787a08d
- 72a9219e82
- 98bb597c05
- c59b70841c
Next cycle we can reland a slightly more narrowly focused variant or one
that focuses on `--emit` instead of `--print native-static-libs`.
But in its current state, I am not sure the warning is very useful.
Fix `PathSource` lifetimes.
It currently has two, which don't accurately capture what's happening -- the `TupleStruct` spans are allocated in `ResolverArenas`, which is different to where the `Expr` is allocated -- and require some "outlives" constraints to be used.
This commit adds another lifetime, renames the existing ones, and removes the "outlives" constraints.
r? `@petrochenkov`
Port `#[rustc_as_ptr]` to the new attribute system
It might make sense to introduce some new parser analogous to `Single`, but even more simple: for parsing attributes that take no arguments and may appear only once (such as `#[rustc_as_ptr]` or `#[rustc_const_stable_indirect]`). Not sure if this should be a single `impl` parsing all such attributes, or one impl per attribute. Or how it will play along with the upcoming rework of attribute validation. Or how these argumentless attributes should be called (I've loosely referred to them as `markers` in the name of the new module in this PR, but not sure how good it is).
This is a part of rust-lang/rust#131229, so
r? `@jdonszelmann`
---
For reference, the `#[rustc_as_ptr]` attribute was created back in rust-lang/rust#132732 as a followup to rust-lang/rust#128985.
Fix RISC-V C function ABI when passing/returning structs containing floats
RISC-V passes structs containing only one or two floats (or a float and integer pair) in registers, as long as the individual floats/integers fit in a single corresponding register (see [the ABI specification](https://github.com/riscv-non-isa/riscv-elf-psabi-doc/releases/download/v1.0/riscv-abi.pdf) for details). Before this PR, Rust would not check what offset the second float/integer was at, instead assuming that it was at the standard offset for its default alignment. However, as the offset can be affected by `#[repr(align(N))]` and `#[repr(packed)]`, this caused miscompilations (see #115609). To fix this, this PR introduces a `rest_offset` field to `CastTarget` that can be used to explicitly specify at what offset the `rest` part of the cast is located at.
While fixing this, I discovered another bug: the size of the cast target was being used as the size of the MIR return place (when the function was using a `PassMode::Cast` return type). However, the cast target is allowed to be smaller than the size of the actual type, causing a miscompilation. This PR fixes this issue by using the largest of the size of the type and the size of the cast target as the size of the MIR return place, ensuring all reads/writes will be inbounds.
Fixes the RISC-V part of #115609.
cc target maintainers of `riscv64gc-unknown-linux-gnu`: `@kito-cheng` `@michaelmaitland` `@robin-randhawa-sifive` `@topperc`
r? `@workingjubilee`
Expand the automatic implementation of `MetaSized` and `PointeeSized` so
that it is also implemented on non-`Sized` types, just not `ty::Foreign`
(extern type).
Introduce the `MetaSized` and `PointeeSized` traits as supertraits of
`Sized` and initially implement it on everything that currently
implements `Sized` to isolate any changes that simply adding the
traits introduces.
