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Fix -Z print-type-sizes's handling of zero-sized fields. #67215

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merged 1 commit into from
Dec 12, 2019
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Fix -Z print-type-sizes's handling of zero-sized fields. #67215

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9 changes: 6 additions & 3 deletions src/librustc_session/code_stats.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -132,9 +132,12 @@ impl CodeStats {

let mut min_offset = discr_size;

// We want to print fields by increasing offset.
// We want to print fields by increasing offset. We also want
// zero-sized fields before non-zero-sized fields, otherwise
// the loop below goes wrong; hence the `f.size` in the sort
// key.
let mut fields = fields.clone();
fields.sort_by_key(|f| f.offset);
fields.sort_by_key(|f| (f.offset, f.size));

for field in fields.iter() {
let FieldInfo { ref name, offset, size, align } = *field;
Expand All @@ -146,7 +149,7 @@ impl CodeStats {
}

if offset < min_offset {
// if this happens something is very wrong
// If this happens it's probably a union.
println!("print-type-size {}field `.{}`: {} bytes, \
offset: {} bytes, \
alignment: {} bytes",
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46 changes: 46 additions & 0 deletions src/test/ui/print_type_sizes/zero-sized-fields.rs
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@@ -0,0 +1,46 @@
// compile-flags: -Z print-type-sizes
// build-pass (FIXME(62277): could be check-pass?)

// At one point, zero-sized fields such as those in this file were causing
// incorrect output from `-Z print-type-sizes`.

#![feature(start)]

struct S1 {
x: u32,
y: u32,
tag: (),
}

struct Void();
struct Empty {}

struct S5<TagW, TagZ> {
tagw: TagW,
w: u32,
unit: (),
x: u32,
void: Void,
y: u32,
empty: Empty,
z: u32,
tagz: TagZ,
}

#[start]
fn start(_: isize, _: *const *const u8) -> isize {
let _s1: S1 = S1 { x: 0, y: 0, tag: () };

let _s5: S5<(), Empty> = S5 {
tagw: (),
w: 1,
unit: (),
x: 2,
void: Void(),
y: 3,
empty: Empty {},
z: 4,
tagz: Empty {},
};
0
}
16 changes: 16 additions & 0 deletions src/test/ui/print_type_sizes/zero-sized-fields.stdout
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Original file line number Diff line number Diff line change
@@ -0,0 +1,16 @@
print-type-size type: `S5<(), Empty>`: 16 bytes, alignment: 4 bytes
print-type-size field `.tagw`: 0 bytes
print-type-size field `.unit`: 0 bytes
print-type-size field `.void`: 0 bytes
print-type-size field `.empty`: 0 bytes
print-type-size field `.tagz`: 0 bytes
print-type-size field `.w`: 4 bytes
print-type-size field `.x`: 4 bytes
print-type-size field `.y`: 4 bytes
print-type-size field `.z`: 4 bytes
print-type-size type: `S1`: 8 bytes, alignment: 4 bytes
print-type-size field `.tag`: 0 bytes
print-type-size field `.x`: 4 bytes
print-type-size field `.y`: 4 bytes
print-type-size type: `Empty`: 0 bytes, alignment: 1 bytes
print-type-size type: `Void`: 0 bytes, alignment: 1 bytes