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For example, transmuting between `bool` and `Ordering` doesn't need two `assume`s because one range is a superset of the other.
Multiple are still used for things like `char` <-> `NonZero<u32>`, which overlap but where neither fully contains the other.
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Allow custom default address spaces and parse `p-` specifications in the datalayout string
Some targets, such as CHERI, use as default an address space different from the "normal" default address space `0` (in the case of CHERI, [200 is used](https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-877.pdf)). Currently, `rustc` does not allow to specify custom address spaces and does not take into consideration [`p-` specifications in the datalayout string](https://llvm.org/docs/LangRef.html#langref-datalayout).
This patch tries to mitigate these problems by allowing targets to define a custom default address space (while keeping the default value to address space `0`) and adding the code to parse the `p-` specifications in `rustc_abi`. The main changes are that `TargetDataLayout` now uses functions to refer to pointer-related informations, instead of having specific fields for the size and alignment of pointers in the default address space; furthermore, the two `pointer_size` and `pointer_align` fields in `TargetDataLayout` are replaced with an `FxHashMap` that holds info for all the possible address spaces, as parsed by the `p-` specifications.
The potential performance drawbacks of not having ad-hoc fields for the default address space will be tested in this PR's CI run.
r? workingjubilee
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default data address space
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We will want to remove many cases of `.abi`, including `.abi.thing`,
so this may simplify future PRs and certainly doesn't hurt.
We omit DerefMut because mutation is much rarer and localized.
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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.
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It was already available as a generic parameter anyway, and it's not like we'll ever put a tag in the 5-billionth field.
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Add a .bss-like scheme for encoded const allocs
This check if all bytes are zero feel like it should be too slow, and instead we should have a flag that we track, but that seems hard. Let's see how this perfs first.
Also we can probably stash the "it's all zero actually" flag inside one of the other struct members that's already not using an entire byte. This optimization doesn't fire all that often, so it's possible that by sticking it in the varint length field, this PR actually makes rmeta size worse.
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It's no longer necessary now that `-Wunreachable_pub` is being passed.
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Revert <https://github.com/rust-lang/rust/pull/138084> to buy time to
consider options that avoids breaking downstream usages of cargo on
distributed `rustc-src` artifacts, where such cargo invocations fail due
to inability to inherit `lints` from workspace root manifest's
`workspace.lints` (this is only valid for the source rust-lang/rust
workspace, but not really the distributed `rustc-src` artifacts).
This breakage was reported in
<https://github.com/rust-lang/rust/issues/138304>.
This reverts commit 48caf81484b50dca5a5cebb614899a3df81ca898, reversing
changes made to c6662879b27f5161e95f39395e3c9513a7b97028.
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Move more layouting logic to `rustc_abi`
Move all `LayoutData`-constructing code to `rustc_abi`:
- Infaillible operations get a new `LayoutData` constructor method;
- Faillible ones get a new method on `LayoutCalculator`.
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...either as:
- methods on LayoutCalculator, for faillible operations;
- constructors on LayoutData, for infaillible ones.
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(Except for `rustc_codegen_cranelift`.)
It's no longer necessary now that `unreachable_pub` is in the workspace
lints.
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adjust Layout debug printing to match the internal field name
The field got renamed a while ago, but the debug printing was not updated to match.
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r=saethlin,traviscross
Greatly simplify lifetime captures in edition 2024
Remove most of the `+ Captures` and `+ '_` from the compiler, since they are now unnecessary with the new edition 2021 lifetime capture rules. Use some `+ 'tcx` and `+ 'static` rather than being overly verbose with precise capturing syntax.
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r=bjorn3,RalfJung
compiler: untangle SIMD alignment assumptions
There were a number of puzzling assumptions being made about SIMD types and their layout that I have corrected in this diff. These are mostly no-op edits in actual fact, but they do subtly alter a pair of checks in our invariant-checking and union layout computation that rested on those peculiar assumptions. Those unfortunately stand in the way of any further actual fixes. I submit this for review, even though it's not clearly motivated without its followups, because it should still be possible to independently conclude whether this is correct.
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Introduce a pair of functions that actually describe what they do,
because it wasn't clear the alignment is sometimes a forgery.
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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.
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No functional changes.
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Co-authored-by: Jubilee <workingjubilee@gmail.com>
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field in `LayoutData`.
Also update comments that refered to BackendRepr::Uninhabited.
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with rust-analyzer
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These can be entirely replaced by the FromStr implementation.
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These were a way to ensure hashes were stable over time for ExternAbi,
but simply hashing the strings is more stable in the face of changes.
As a result, we can do away with them.
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By moving this stability check into AST lowering, we effectively make
it impossible to accidentally miss, as it must happen to generate HIR.
Also, we put the ABI-stability code next to code that actually uses it!
This allows code that wants to reason about backend ABI implementations
to stop worrying about high-level concerns like syntax stability,
while still leaving it as the authority on what ABIs actually exist.
It also makes it easy to refactor things to have more consistent errors.
For now, we only apply this to generalize the existing messages a bit.
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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
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