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rustc: don't use union layouts for tagged union enums. #47007

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Dec 27, 2017
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rustc: don't use union layouts for tagged union enums. #47007

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8 changes: 4 additions & 4 deletions src/librustc/ty/layout.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1655,10 +1655,10 @@ impl<'a, 'tcx> LayoutDetails {
discr,
variants
},
// FIXME(eddyb): using `FieldPlacement::Arbitrary` here results
// in lost optimizations, specifically around allocations, see
// `test/codegen/{alloc-optimisation,vec-optimizes-away}.rs`.
fields: FieldPlacement::Union(1),
fields: FieldPlacement::Arbitrary {
offsets: vec![Size::from_bytes(0)],
memory_index: vec![0]
},
abi,
align,
size
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5 changes: 3 additions & 2 deletions src/test/codegen/align-struct.rs
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Expand Up @@ -32,13 +32,14 @@ pub enum Enum4 {
A(i32),
B(i32),
}
// CHECK: %Enum4 = type { [2 x i32] }
// CHECK: %Enum4 = type { [0 x i32], i32, [1 x i32] }
// CHECK: %"Enum4::A" = type { [1 x i32], i32, [0 x i32] }

pub enum Enum64 {
A(Align64),
B(i32),
}
// CHECK: %Enum64 = type { [16 x i64] }
// CHECK: %Enum64 = type { [0 x i32], i32, [31 x i32] }
// CHECK: %"Enum64::A" = type { [8 x i64], %Align64, [0 x i64] }

// CHECK-LABEL: @align64
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