Make struct layout not depend on unsizeable tail
fixes (after backport) https://github.com/rust-lang/rust/issues/112048
Since unsizing `Ptr<Foo<T>>` -> `Ptr<Foo<U>` just copies the pointer and adds the metadata, the layout of `Foo` must not depend on niches in and alignment of the tail `T`.
Nominating for beta 1.71, because it will have this issue: `@rustbot` label beta-nominated
Error message all end up passing into a function as an `impl
Into<{D,Subd}iagnosticMessage>`. If an error message is creatd as
`&format("...")` that means we allocate a string (in the `format!`
call), then take a reference, and then clone (allocating again) the
reference to produce the `{D,Subd}iagnosticMessage`, which is silly.
This commit removes the leading `&` from a lot of these cases. This
means the original `String` is moved into the
`{D,Subd}iagnosticMessage`, avoiding the double allocations. This
requires changing some function argument types from `&str` to `String`
(when all arguments are `String`) or `impl
Into<{D,Subd}iagnosticMessage>` (when some arguments are `String` and
some are `&str`).
For start-biased layout we want to avoid overpromoting so that
the niche doesn't get pushed back.
For end-biased layout we want to avoid promoting fields that
may contain one of the niches of interest.
Various minor Idx-related tweaks
Nothing particularly exciting here, but a couple of things I noticed as I was looking for more index conversions to simplify.
cc https://github.com/rust-lang/compiler-team/issues/606
r? `@WaffleLapkin`
The first PR for https://github.com/rust-lang/compiler-team/issues/606
This is just the move-and-rename, because it's plenty big-and-bitrotty already. Future PRs will start using `FieldIdx` more broadly, and concomitantly removing `FieldIdx::new`s.
Since structs are always `VariantIdx(0)`, there's a bunch of files where the only reason they had `VariantIdx` or `vec::Idx` imported at all was to get the first variant.
So this uses a constant for that, and adds some doc-comments to `VariantIdx` while I'm there, since it doesn't have any today.
Previously, there were two queries to check whether a type allows the
0x01 or zeroed bitpattern.
I am planning on adding a further initness to check, truly uninit for
MaybeUninit, which would make this three queries. This seems overkill
for such a small feature, so this PR unifies them into one.
Default `repr(C)` enums to `c_int` size
This is what ISO C strongly implies this is correct, and
many processor-specific ABIs imply or mandate this size, so
"everyone" (LLVM, gcc...) defaults to emitting enums this way.
However, this is by no means guaranteed by ISO C,
and the bare-metal Arm targets show it can be overridden,
which rustc supports via `c-enum-min-bits` in a target.json.
The override is a flag named `-fshort-enums` in clang and gcc,
but introducing a CLI flag is probably unnecessary for rustc.
This flag can be used by non-Arm microcontroller targets,
like AVR and MSP430, but it is not enabled for them by default.
Rust programmers who know the size of a target's enums
can use explicit reprs, which also lets them match C23 code.
This change is most relevant to 16-bit targets: AVR and MSP430.
Most of rustc's targets use 32-bit ints, but ILP64 does exist.
Regardless, rustc should now correctly handle enums for
both very small and very large targets.
Thanks to William for confirming MSP430 behavior,
and to Waffle for better style and no-core `size_of` asserts.
Fixesrust-lang/rust#107361Fixesrust-lang/rust#77806
This is what ISO C strongly implies this is correct, and
many processor-specific ABIs imply or mandate this size, so
"everyone" (LLVM, gcc...) defaults to emitting enums this way.
However, this is by no means guaranteed by ISO C,
and the bare-metal Arm targets show it can be overridden,
which rustc supports via `c-enum-min-bits` in a target.json.
The override is a flag named `-fshort-enums` in clang and gcc,
but introducing a CLI flag is probably unnecessary for rustc.
This flag can be used by non-Arm microcontroller targets,
like AVR and MSP430, but it is not enabled for them by default.
Rust programmers who know the size of a target's enums
can use explicit reprs, which also lets them match C23 code.
This change is most relevant to 16-bit targets: AVR and MSP430.
Most of rustc's targets use 32-bit ints, but ILP64 does exist.
Regardless, rustc should now correctly handle enums for
both very small and very large targets.
Thanks to William for confirming MSP430 behavior,
and to Waffle for better style and no-core size_of asserts.
Co-authored-by: William D. Jones <thor0505@comcast.net>
Co-authored-by: Waffle Maybe <waffle.lapkin@gmail.com>
The code that consumes PointerKind (`adjust_for_rust_scalar` in rustc_ty_utils)
ended up using PointerKind variants to talk about Rust reference types (& and
&mut) anyway, making the old code structure quite confusing: one always had to
keep in mind which PointerKind corresponds to which type. So this changes
PointerKind to directly reflect the type.
This does not change behavior.
...and remove it from `PointeeInfo`, which isn't meant for this.
There are still various places (marked with FIXMEs) that assume all pointers
have the same size and alignment. Fixing this requires parsing non-default
address spaces in the data layout string, which will be done in a followup.
there were fixmes for this already
i am about to remove is_ptr (since callers need to properly distinguish
between pointers in different address spaces), so might as well do this
at the same time
