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layout: Avoid niches that make things worse. #63903

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layout: Avoid niches that make things worse. #63903

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0ac9003
layout: Factor out a utility function.
hvenev Aug 25, 2019
efc446f
layout: Always use the largest tag size that fits.
hvenev Aug 25, 2019
ed45921
layout: Avoid niches that make things worse.
hvenev Aug 25, 2019
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284 changes: 130 additions & 154 deletions src/librustc/ty/layout.rs
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10 changes: 10 additions & 0 deletions src/librustc_target/abi/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -533,6 +533,16 @@ impl Integer {
}
I8
}

/// Finds the largest integer with the given size or less.
pub fn approximate_size(wanted: Size) -> Option<Integer> {
for &candidate in &[I64, I32, I16, I8] {
if wanted >= candidate.size() {
return Some(candidate);
}
}
None
}
}


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2 changes: 1 addition & 1 deletion src/test/codegen/align-enum.rs
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Expand Up @@ -9,7 +9,7 @@ pub enum Align64 {
A(u32),
B(u32),
}
// CHECK: %Align64 = type { [0 x i32], i32, [15 x i32] }
// CHECK: %Align64 = type { [0 x i64], i64, [7 x i64] }

pub struct Nested64 {
a: u8,
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11 changes: 10 additions & 1 deletion src/test/codegen/align-struct.rs
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Expand Up @@ -26,8 +26,9 @@ pub enum Enum64 {
A(Align64),
B(i32),
}
// CHECK: %Enum64 = type { [0 x i32], i32, [31 x i32] }
// CHECK: %Enum64 = type { [0 x i64], i64, [15 x i64] }
// CHECK: %"Enum64::A" = type { [8 x i64], %Align64, [0 x i64] }
// CHECK: %"Enum64::B" = type { [2 x i32], i32, [1 x i32] }

// CHECK-LABEL: @align64
#[no_mangle]
Expand Down Expand Up @@ -71,3 +72,11 @@ pub fn enum64(a: Align64) -> Enum64 {
let e64 = Enum64::A(a);
e64
}

// CHECK-LABEL: @enum64_b
#[no_mangle]
pub fn enum64_b(b: i32) -> Enum64 {
// CHECK: %e64 = alloca %Enum64, align 64
let e64 = Enum64::B(b);
e64
}
12 changes: 11 additions & 1 deletion src/test/ui/print_type_sizes/niche-filling.rs
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Expand Up @@ -27,7 +27,7 @@ impl<T> Default for MyOption<T> {

pub enum EmbeddedDiscr {
None,
Record { pre: u8, val: NonZeroU32, post: u16 },
Record { pre1: u8, pre2: u8, val: NonZeroU32, post: u16 },
}

impl Default for EmbeddedDiscr {
Expand All @@ -53,6 +53,15 @@ impl Default for NestedNonZero {
}
}

pub enum BadNiche {
None,
Record { pre: u8, val: NonZeroU32, post: u16 },
}

impl Default for BadNiche {
fn default() -> Self { BadNiche::None }
}

pub enum Enum4<A, B, C, D> {
One(A),
Two(B),
Expand All @@ -74,6 +83,7 @@ fn start(_: isize, _: *const *const u8) -> isize {
let _x: MyOption<NonZeroU32> = Default::default();
let _y: EmbeddedDiscr = Default::default();
let _z: MyOption<IndirectNonZero> = Default::default();
let _w: BadNiche = Default::default();
let _a: MyOption<bool> = Default::default();
let _b: MyOption<char> = Default::default();
let _c: MyOption<std::cmp::Ordering> = Default::default();
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13 changes: 10 additions & 3 deletions src/test/ui/print_type_sizes/niche-filling.stdout
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Expand Up @@ -7,13 +7,20 @@ print-type-size type: `MyOption<IndirectNonZero>`: 12 bytes, alignment: 4 bytes
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 type: `BadNiche`: 8 bytes, alignment: 4 bytes
print-type-size discriminant: 1 bytes
print-type-size variant `Record`: 7 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 type: `EmbeddedDiscr`: 8 bytes, alignment: 4 bytes
print-type-size variant `Record`: 8 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 `.pre1`: 1 bytes
print-type-size field `.pre2`: 1 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
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22 changes: 10 additions & 12 deletions src/test/ui/print_type_sizes/padding.stdout
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Original file line number Diff line number Diff line change
@@ -1,21 +1,19 @@
print-type-size type: `E1`: 12 bytes, alignment: 4 bytes
print-type-size discriminant: 1 bytes
print-type-size variant `B`: 11 bytes
print-type-size padding: 3 bytes
print-type-size field `.0`: 8 bytes, alignment: 4 bytes
print-type-size variant `A`: 7 bytes
print-type-size discriminant: 4 bytes
print-type-size variant `A`: 8 bytes
print-type-size field `.1`: 1 bytes
print-type-size padding: 2 bytes
print-type-size padding: 3 bytes
print-type-size field `.0`: 4 bytes, alignment: 4 bytes
print-type-size variant `B`: 8 bytes
print-type-size field `.0`: 8 bytes
print-type-size type: `E2`: 12 bytes, alignment: 4 bytes
print-type-size discriminant: 1 bytes
print-type-size variant `B`: 11 bytes
print-type-size padding: 3 bytes
print-type-size field `.0`: 8 bytes, alignment: 4 bytes
print-type-size variant `A`: 7 bytes
print-type-size discriminant: 4 bytes
print-type-size variant `A`: 8 bytes
print-type-size field `.0`: 1 bytes
print-type-size padding: 2 bytes
print-type-size padding: 3 bytes
print-type-size field `.1`: 4 bytes, alignment: 4 bytes
print-type-size variant `B`: 8 bytes
print-type-size field `.0`: 8 bytes
print-type-size type: `S`: 8 bytes, alignment: 4 bytes
print-type-size field `.g`: 4 bytes
print-type-size field `.a`: 1 bytes
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6 changes: 3 additions & 3 deletions src/test/ui/print_type_sizes/repr-align.stdout
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@@ -1,7 +1,7 @@
print-type-size type: `E`: 32 bytes, alignment: 16 bytes
print-type-size discriminant: 4 bytes
print-type-size variant `B`: 28 bytes
print-type-size padding: 12 bytes
print-type-size discriminant: 8 bytes
print-type-size variant `B`: 24 bytes
print-type-size padding: 8 bytes
print-type-size field `.0`: 16 bytes, alignment: 16 bytes
print-type-size variant `A`: 4 bytes
print-type-size field `.0`: 4 bytes
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