diff options
| -rw-r--r-- | src/librustc_middle/lib.rs | 1 | ||||
| -rw-r--r-- | src/librustc_middle/ty/layout.rs | 16 | ||||
| -rw-r--r-- | src/test/ui/print_type_sizes/niche-filling.stdout | 6 | ||||
| -rw-r--r-- | src/test/ui/type-sizes.rs | 17 |
4 files changed, 36 insertions, 4 deletions
diff --git a/src/librustc_middle/lib.rs b/src/librustc_middle/lib.rs index b7dccb8d8ce..a68301385b7 100644 --- a/src/librustc_middle/lib.rs +++ b/src/librustc_middle/lib.rs @@ -27,6 +27,7 @@ #![feature(bool_to_option)] #![feature(box_patterns)] #![feature(box_syntax)] +#![feature(cmp_min_max_by)] #![feature(const_fn)] #![feature(const_panic)] #![feature(const_fn_transmute)] diff --git a/src/librustc_middle/ty/layout.rs b/src/librustc_middle/ty/layout.rs index daa9918a396..8ae9269a6bf 100644 --- a/src/librustc_middle/ty/layout.rs +++ b/src/librustc_middle/ty/layout.rs @@ -1233,7 +1233,21 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> { size, }; - tcx.intern_layout(niche_filling_layout.unwrap_or(tagged_layout)) + let best_layout = match (tagged_layout, niche_filling_layout) { + (tagged_layout, Some(niche_filling_layout)) => { + // Pick the smaller layout; otherwise, + // pick the layout with the larger niche; otherwise, + // pick tagged as it has simpler codegen. + cmp::min_by_key(tagged_layout, niche_filling_layout, |layout| { + let niche_size = + layout.largest_niche.as_ref().map_or(0, |n| n.available(dl)); + (layout.size, cmp::Reverse(niche_size)) + }) + } + (tagged_layout, None) => tagged_layout, + }; + + tcx.intern_layout(best_layout) } // Types with no meaningful known layout. diff --git a/src/test/ui/print_type_sizes/niche-filling.stdout b/src/test/ui/print_type_sizes/niche-filling.stdout index 301edc0d086..1894cd218ee 100644 --- a/src/test/ui/print_type_sizes/niche-filling.stdout +++ b/src/test/ui/print_type_sizes/niche-filling.stdout @@ -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 diff --git a/src/test/ui/type-sizes.rs b/src/test/ui/type-sizes.rs index 6a3f3c98f12..0ae9bfcf0bd 100644 --- a/src/test/ui/type-sizes.rs +++ b/src/test/ui/type-sizes.rs @@ -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); } |