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Disable field reordering for repr(int). #56887

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Dec 22, 2018
Merged

Disable field reordering for repr(int). #56887

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fba23d0
Disable field reordering for repr(int).
emilio Dec 16, 2018
d84bdba
Add test to check order of repr(int) enum fields
petertodd Dec 8, 2018
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5 changes: 3 additions & 2 deletions src/librustc/ty/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2059,9 +2059,10 @@ impl ReprOptions {
}

/// Returns `true` if this `#[repr()]` should inhibit struct field reordering
/// optimizations, such as with repr(C) or repr(packed(1)).
/// optimizations, such as with repr(C), repr(packed(1)), or repr(<int>).
pub fn inhibit_struct_field_reordering_opt(&self) -> bool {
!(self.flags & ReprFlags::IS_UNOPTIMISABLE).is_empty() || (self.pack == 1)
self.flags.intersects(ReprFlags::IS_UNOPTIMISABLE) || self.pack == 1 ||
self.int.is_some()
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@eddyb eddyb Dec 19, 2018 •
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cc @rkruppe @nagisa This seems somewhat fragile (I mean the pre-existing code).
The check for pack == 1 means things will still be reordered with #[repr(packed(N))], is that intentional?
Also, it seems to me that inhibit_enum_layout_opt is a subset of this function and maybe we should have just one function that checks all conditions?

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@nagisa nagisa Dec 19, 2018 •
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The repr RFC does not specify any behaviour /wrt repr(packed(N)) for enums and I’m not sure I recall us guaranteeing that repr(packed) specifies any representation and the reference seems to agree.

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In fact as per strict reading of the reference, self.pack == 1 inhibiting reordering would be somewhat wrong, as it should cause "packing" for the original ordering, but since the "default" ordering is not specified, it seems to be fine either way...

}

/// Returns true if this `#[repr()]` should inhibit union abi optimisations
Expand Down
18 changes: 10 additions & 8 deletions src/test/run-pass/structs-enums/enum-non-c-like-repr-c-and-int.rs
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Expand Up @@ -20,11 +20,12 @@ use std::mem;
#[repr(C, u8)]
#[derive(Copy, Clone, Eq, PartialEq, Debug)]
enum MyEnum {
A(u32), // Single primitive value
B { x: u8, y: i16 }, // Composite, and the offset of `y` depends on tag being internal
C, // Empty
D(Option<u32>), // Contains an enum
E(Duration), // Contains a struct
A(u32), // Single primitive value
B { x: u8, y: i16, z: u8 }, // Composite, and the offsets of `y` and `z`
// depend on tag being internal
C, // Empty
D(Option<u32>), // Contains an enum
E(Duration), // Contains a struct
}

#[repr(C)]
Expand All @@ -44,14 +45,14 @@ union MyEnumPayload {

#[repr(u8)] #[derive(Copy, Clone)] enum MyEnumTag { A, B, C, D, E }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantA(u32);
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantB {x: u8, y: i16 }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantB {x: u8, y: i16, z: u8 }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantD(Option<u32>);
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantE(Duration);

fn main() {
let result: Vec<Result<MyEnum, ()>> = vec![
Ok(MyEnum::A(17)),
Ok(MyEnum::B { x: 206, y: 1145 }),
Ok(MyEnum::B { x: 206, y: 1145, z: 78 }),
Ok(MyEnum::C),
Err(()),
Ok(MyEnum::D(Some(407))),
Expand All @@ -63,7 +64,7 @@ fn main() {
// Binary serialized version of the above (little-endian)
let input: Vec<u8> = vec![
0, 17, 0, 0, 0,
1, 206, 121, 4,
1, 206, 121, 4, 78,
2,
8, /* invalid tag value */
3, 0, 151, 1, 0, 0,
Expand Down Expand Up @@ -112,6 +113,7 @@ fn parse_my_enum<'a>(dest: &'a mut MyEnum, buf: &mut &[u8]) -> Result<(), ()> {
MyEnumTag::B => {
dest.payload.B.x = read_u8(buf)?;
dest.payload.B.y = read_u16_le(buf)? as i16;
dest.payload.B.z = read_u8(buf)?;
}
MyEnumTag::C => {
/* do nothing */
Expand Down
18 changes: 10 additions & 8 deletions src/test/run-pass/structs-enums/enum-non-c-like-repr-c.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,11 +20,12 @@ use std::mem;
#[repr(C)]
#[derive(Copy, Clone, Eq, PartialEq, Debug)]
enum MyEnum {
A(u32), // Single primitive value
B { x: u8, y: i16 }, // Composite, and the offset of `y` depends on tag being internal
C, // Empty
D(Option<u32>), // Contains an enum
E(Duration), // Contains a struct
A(u32), // Single primitive value
B { x: u8, y: i16, z: u8 }, // Composite, and the offset of `y` and `z`
// depend on tag being internal
C, // Empty
D(Option<u32>), // Contains an enum
E(Duration), // Contains a struct
}

#[repr(C)]
Expand All @@ -44,14 +45,14 @@ union MyEnumPayload {

#[repr(C)] #[derive(Copy, Clone)] enum MyEnumTag { A, B, C, D, E }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantA(u32);
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantB {x: u8, y: i16 }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantB {x: u8, y: i16, z: u8 }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantD(Option<u32>);
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantE(Duration);

fn main() {
let result: Vec<Result<MyEnum, ()>> = vec![
Ok(MyEnum::A(17)),
Ok(MyEnum::B { x: 206, y: 1145 }),
Ok(MyEnum::B { x: 206, y: 1145, z: 78 }),
Ok(MyEnum::C),
Err(()),
Ok(MyEnum::D(Some(407))),
Expand All @@ -63,7 +64,7 @@ fn main() {
// Binary serialized version of the above (little-endian)
let input: Vec<u8> = vec![
0, 17, 0, 0, 0,
1, 206, 121, 4,
1, 206, 121, 4, 78,
2,
8, /* invalid tag value */
3, 0, 151, 1, 0, 0,
Expand Down Expand Up @@ -112,6 +113,7 @@ fn parse_my_enum<'a>(dest: &'a mut MyEnum, buf: &mut &[u8]) -> Result<(), ()> {
MyEnumTag::B => {
dest.payload.B.x = read_u8(buf)?;
dest.payload.B.y = read_u16_le(buf)? as i16;
dest.payload.B.z = read_u8(buf)?;
}
MyEnumTag::C => {
/* do nothing */
Expand Down
18 changes: 10 additions & 8 deletions src/test/run-pass/structs-enums/enum-non-c-like-repr-int.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,11 +20,12 @@ use std::mem;
#[repr(u8)]
#[derive(Copy, Clone, Eq, PartialEq, Debug)]
enum MyEnum {
A(u32), // Single primitive value
B { x: u8, y: i16 }, // Composite, and the offset of `y` depends on tag being internal
C, // Empty
D(Option<u32>), // Contains an enum
E(Duration), // Contains a struct
A(u32), // Single primitive value
B { x: u8, y: i16, z: u8 }, // Composite, and the offset of `y` and `z`
// depend on tag being internal
C, // Empty
D(Option<u32>), // Contains an enum
E(Duration), // Contains a struct
}

#[allow(non_snake_case)]
Expand All @@ -39,15 +40,15 @@ union MyEnumRepr {

#[repr(u8)] #[derive(Copy, Clone)] enum MyEnumTag { A, B, C, D, E }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantA(MyEnumTag, u32);
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantB { tag: MyEnumTag, x: u8, y: i16 }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantB { tag: MyEnumTag, x: u8, y: i16, z: u8 }
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantC(MyEnumTag);
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantD(MyEnumTag, Option<u32>);
#[repr(C)] #[derive(Copy, Clone)] struct MyEnumVariantE(MyEnumTag, Duration);

fn main() {
let result: Vec<Result<MyEnum, ()>> = vec![
Ok(MyEnum::A(17)),
Ok(MyEnum::B { x: 206, y: 1145 }),
Ok(MyEnum::B { x: 206, y: 1145, z: 78 }),
Ok(MyEnum::C),
Err(()),
Ok(MyEnum::D(Some(407))),
Expand All @@ -59,7 +60,7 @@ fn main() {
// Binary serialized version of the above (little-endian)
let input: Vec<u8> = vec![
0, 17, 0, 0, 0,
1, 206, 121, 4,
1, 206, 121, 4, 78,
2,
8, /* invalid tag value */
3, 0, 151, 1, 0, 0,
Expand Down Expand Up @@ -108,6 +109,7 @@ fn parse_my_enum<'a>(dest: &'a mut MyEnum, buf: &mut &[u8]) -> Result<(), ()> {
MyEnumTag::B => {
dest.B.x = read_u8(buf)?;
dest.B.y = read_u16_le(buf)? as i16;
dest.B.z = read_u8(buf)?;
}
MyEnumTag::C => {
/* do nothing */
Expand Down