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compare tagged/niche-filling layout and pick the best one

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This commit is contained in:
Erik Desjardins 2020-07-05 14:29:30 -04:00
parent b0a7fbd91f
commit 2e431c62b6
4 changed files with 36 additions and 4 deletions
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6
src/test/ui/print_type_sizes/niche-filling.stdout
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@ -8,12 +8,12 @@ print-type-size variant `Some`: 12 bytes
print-type-size field `.0`: 12 bytes
print-type-size variant `None`: 0 bytes
print-type-size type: `EmbeddedDiscr`: 8 bytes, alignment: 4 bytes
print-type-size discriminant: 1 bytes
print-type-size variant `Record`: 7 bytes
print-type-size field `.val`: 4 bytes
print-type-size field `.post`: 2 bytes
print-type-size field `.pre`: 1 bytes
print-type-size field `.post`: 2 bytes
print-type-size field `.val`: 4 bytes
print-type-size variant `None`: 0 bytes
print-type-size end padding: 1 bytes
print-type-size type: `MyOption<Union1<std::num::NonZeroU32>>`: 8 bytes, alignment: 4 bytes
print-type-size discriminant: 4 bytes
print-type-size variant `Some`: 4 bytes

17
src/test/ui/type-sizes.rs
View file

@ -5,6 +5,7 @@
#![feature(never_type)]
use std::mem::size_of;
use std::num::NonZeroU8;
struct t {a: u8, b: i8}
struct u {a: u8, b: i8, c: u8}
@ -102,6 +103,15 @@ enum Option2<A, B> {
None
}
pub enum CanBeNicheFilledButShouldnt {
A(NonZeroU8, u32),
B
}
pub enum AlwaysTagged {
A(u8, u32),
B
}
pub fn main() {
assert_eq!(size_of::<u8>(), 1 as usize);
assert_eq!(size_of::<u32>(), 4 as usize);
@ -145,4 +155,11 @@ pub fn main() {
assert_eq!(size_of::<Option<Option<(&(), bool)>>>(), size_of::<(bool, &())>());
assert_eq!(size_of::<Option<Option2<bool, &()>>>(), size_of::<(bool, &())>());
assert_eq!(size_of::<Option<Option2<&(), bool>>>(), size_of::<(bool, &())>());
assert_eq!(size_of::<CanBeNicheFilledButShouldnt>(), 8);
assert_eq!(size_of::<Option<CanBeNicheFilledButShouldnt>>(), 8);
assert_eq!(size_of::<Option<Option<CanBeNicheFilledButShouldnt>>>(), 8);
assert_eq!(size_of::<AlwaysTagged>(), 8);
assert_eq!(size_of::<Option<AlwaysTagged>>(), 8);
assert_eq!(size_of::<Option<Option<AlwaysTagged>>>(), 8);
}