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Auto merge of #57998 - niklasf:align-enum, r=nagisa
Allow #[repr(align(x))] on enums (#57996) Tracking issue: #57996 Implements an extension of [RFC 1358](https://github.com/rust-lang/rfcs/blob/master/text/1358-repr-align.md) behind a feature flag (`repr_align_enum`). Originally introduced here for structs: #39999. It seems like only HIR-level changes are required, since enums are already aware of their alignment (due to alignment of their limbs). cc @bitshifter
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src/doc/unstable-book/src/language-features/repr-align-enum.md
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# `repr_align_enum` | ||
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The tracking issue for this feature is: [#57996] | ||
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[#57996]: https://github.com/rust-lang/rust/issues/57996 | ||
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------------------------ | ||
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The `repr_align_enum` feature allows using the `#[repr(align(x))]` attribute | ||
on enums, similarly to structs. | ||
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# Examples | ||
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```rust | ||
#![feature(repr_align_enum)] | ||
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#[repr(align(8))] | ||
enum Aligned { | ||
Foo, | ||
Bar { value: u32 }, | ||
} | ||
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fn main() { | ||
assert_eq!(std::mem::align_of::<Aligned>(), 8); | ||
} | ||
``` | ||
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This is equivalent to using an aligned wrapper struct everywhere: | ||
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```rust | ||
#[repr(align(8))] | ||
struct Aligned(Unaligned); | ||
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enum Unaligned { | ||
Foo, | ||
Bar { value: u32 }, | ||
} | ||
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fn main() { | ||
assert_eq!(std::mem::align_of::<Aligned>(), 8); | ||
} | ||
``` |
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// compile-flags: -C no-prepopulate-passes | ||
// ignore-tidy-linelength | ||
// min-llvm-version 7.0 | ||
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#![crate_type = "lib"] | ||
#![feature(repr_align_enum)] | ||
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#[repr(align(64))] | ||
pub enum Align64 { | ||
A(u32), | ||
B(u32), | ||
} | ||
// CHECK: %Align64 = type { [0 x i32], i32, [15 x i32] } | ||
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pub struct Nested64 { | ||
a: u8, | ||
b: Align64, | ||
c: u16, | ||
} | ||
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// CHECK-LABEL: @align64 | ||
#[no_mangle] | ||
pub fn align64(a: u32) -> Align64 { | ||
// CHECK: %a64 = alloca %Align64, align 64 | ||
// CHECK: call void @llvm.memcpy.{{.*}}(i8* align 64 %{{.*}}, i8* align 64 %{{.*}}, i{{[0-9]+}} 64, i1 false) | ||
let a64 = Align64::A(a); | ||
a64 | ||
} | ||
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// CHECK-LABEL: @nested64 | ||
#[no_mangle] | ||
pub fn nested64(a: u8, b: u32, c: u16) -> Nested64 { | ||
// CHECK: %n64 = alloca %Nested64, align 64 | ||
let n64 = Nested64 { a, b: Align64::B(b), c }; | ||
n64 | ||
} |
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// run-pass | ||
#![allow(dead_code)] | ||
#![feature(repr_align_enum)] | ||
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use std::mem; | ||
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// Raising alignment | ||
#[repr(align(16))] | ||
enum Align16 { | ||
Foo { foo: u32 }, | ||
Bar { bar: u32 }, | ||
} | ||
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// Raise alignment by maximum | ||
#[repr(align(1), align(16))] | ||
#[repr(align(32))] | ||
#[repr(align(4))] | ||
enum Align32 { | ||
Foo, | ||
Bar, | ||
} | ||
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// Not reducing alignment | ||
#[repr(align(4))] | ||
enum AlsoAlign16 { | ||
Foo { limb_with_align16: Align16 }, | ||
Bar, | ||
} | ||
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// No niche for discriminant when used as limb | ||
#[repr(align(16))] | ||
struct NoNiche16(u64, u64); | ||
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// Discriminant will require extra space, but enum needs to stay compatible | ||
// with alignment 16 | ||
#[repr(align(1))] | ||
enum AnotherAlign16 { | ||
Foo { limb_with_noniche16: NoNiche16 }, | ||
Bar, | ||
Baz, | ||
} | ||
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fn main() { | ||
assert_eq!(mem::align_of::<Align16>(), 16); | ||
assert_eq!(mem::size_of::<Align16>(), 16); | ||
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assert_eq!(mem::align_of::<Align32>(), 32); | ||
assert_eq!(mem::size_of::<Align32>(), 32); | ||
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assert_eq!(mem::align_of::<AlsoAlign16>(), 16); | ||
assert_eq!(mem::size_of::<AlsoAlign16>(), 16); | ||
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assert_eq!(mem::align_of::<AnotherAlign16>(), 16); | ||
assert_eq!(mem::size_of::<AnotherAlign16>(), 32); | ||
} |
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error[E0517]: attribute should be applied to struct, enum or union | ||
--> $DIR/attr-usage-repr.rs:3:8 | ||
--> $DIR/attr-usage-repr.rs:4:8 | ||
| | ||
LL | #[repr(C)] //~ ERROR: attribute should be applied to struct, enum or union | ||
| ^ | ||
LL | fn f() {} | ||
| --------- not a struct, enum or union | ||
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error[E0517]: attribute should be applied to enum | ||
--> $DIR/attr-usage-repr.rs:15:8 | ||
--> $DIR/attr-usage-repr.rs:16:8 | ||
| | ||
LL | #[repr(i8)] //~ ERROR: attribute should be applied to enum | ||
| ^^ | ||
LL | struct SInt(f64, f64); | ||
| ---------------------- not an enum | ||
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error[E0517]: attribute should be applied to struct or union | ||
--> $DIR/attr-usage-repr.rs:21:8 | ||
| | ||
LL | #[repr(align(8))] //~ ERROR: attribute should be applied to struct | ||
| ^^^^^^^^ | ||
LL | enum EAlign { A, B } | ||
| -------------------- not a struct or union | ||
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error[E0517]: attribute should be applied to struct or union | ||
--> $DIR/attr-usage-repr.rs:24:8 | ||
--> $DIR/attr-usage-repr.rs:25:8 | ||
| | ||
LL | #[repr(packed)] //~ ERROR: attribute should be applied to struct | ||
| ^^^^^^ | ||
LL | enum EPacked { A, B } | ||
| --------------------- not a struct or union | ||
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error[E0517]: attribute should be applied to struct | ||
--> $DIR/attr-usage-repr.rs:27:8 | ||
--> $DIR/attr-usage-repr.rs:28:8 | ||
| | ||
LL | #[repr(simd)] //~ ERROR: attribute should be applied to struct | ||
| ^^^^ | ||
LL | enum ESimd { A, B } | ||
| ------------------- not a struct | ||
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error: aborting due to 5 previous errors | ||
error: aborting due to 4 previous errors | ||
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For more information about this error, try `rustc --explain E0517`. |
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#[repr(align(16))] | ||
struct Foo(u64); | ||
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#[repr(align(8))] //~ ERROR `#[repr(align(x))]` on enums is experimental (see issue #57996) | ||
enum Bar { | ||
Foo { foo: Foo }, | ||
Baz, | ||
} | ||
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fn main() { } |
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src/test/ui/feature-gates/feature-gate-repr_align_enum.stderr
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error[E0658]: `#[repr(align(x))]` on enums is experimental (see issue #57996) | ||
--> $DIR/feature-gate-repr_align_enum.rs:4:1 | ||
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LL | #[repr(align(8))] //~ ERROR `#[repr(align(x))]` on enums is experimental (see issue #57996) | ||
| ^^^^^^^^^^^^^^^^^ | ||
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= help: add #![feature(repr_align_enum)] to the crate attributes to enable | ||
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error: aborting due to previous error | ||
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For more information about this error, try `rustc --explain E0658`. |
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error[E0589]: invalid `repr(align)` attribute: not an unsuffixed integer | ||
--> $DIR/repr-align.rs:3:8 | ||
--> $DIR/repr-align.rs:4:8 | ||
| | ||
LL | #[repr(align(16.0))] //~ ERROR: invalid `repr(align)` attribute: not an unsuffixed integer | ||
| ^^^^^^^^^^^ | ||
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error[E0589]: invalid `repr(align)` attribute: not a power of two | ||
--> $DIR/repr-align.rs:6:8 | ||
--> $DIR/repr-align.rs:7:8 | ||
| | ||
LL | #[repr(align(15))] //~ ERROR: invalid `repr(align)` attribute: not a power of two | ||
| ^^^^^^^^^ | ||
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error[E0589]: invalid `repr(align)` attribute: larger than 2^29 | ||
--> $DIR/repr-align.rs:9:8 | ||
--> $DIR/repr-align.rs:10:8 | ||
| | ||
LL | #[repr(align(4294967296))] //~ ERROR: invalid `repr(align)` attribute: larger than 2^29 | ||
| ^^^^^^^^^^^^^^^^^ | ||
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error: aborting due to 3 previous errors | ||
error[E0589]: invalid `repr(align)` attribute: not a power of two | ||
--> $DIR/repr-align.rs:16:8 | ||
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LL | #[repr(align(15))] //~ ERROR: invalid `repr(align)` attribute: not a power of two | ||
| ^^^^^^^^^ | ||
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error: aborting due to 4 previous errors | ||
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For more information about this error, try `rustc --explain E0589`. |