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GuillaumeGomezGuillaumeGomez
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Rollup merge of rust-lang#96814 - RalfJung:enum-repr-align, r=oli-obk
Fix repr(align) enum handling `enum`, for better or worse, supports `repr(align)`. That has already caused a bug in rust-lang#92464, which was "fixed" in rust-lang#92932, but it turns out that that fix is wrong and caused rust-lang#96185. So this reverts rust-lang#92932 (which fixes rust-lang#96185), and attempts another strategy for fixing rust-lang#92464: special-case enums when doing a cast, re-using the code to load the discriminant rather than assuming that the enum has scalar layout. This works fine for the interpreter. However, rust-lang#92464 contained another testcase that was previously not in the test suite -- and after adding it, it ICEs again. This is not surprising; codegen needs the same patch that I did in the interpreter. Probably this has to happen [around here](https://github.com/rust-lang/rust/blob/d32ce37a171663048a4c4a536803434e40f52bd6/compiler/rustc_codegen_ssa/src/mir/rvalue.rs#L276). Unfortunately I don't know how to do that -- the interpreter can load a discriminant from an operand, but codegen can only do that from a place. `@oli-obk` `@eddyb` `@bjorn3` any idea?
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‎compiler/rustc_middle/src/ty/layout.rs

+3-3
Original file line numberDiff line numberDiff line change
@@ -1418,9 +1418,9 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
14181418

14191419
if layout_variants.iter().all(|v| v.abi.is_uninhabited()) {
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abi = Abi::Uninhabited;
1421-
} else if tag.size(dl) == size || variants.iter().all(|layout| layout.is_empty()) {
1422-
// Without latter check aligned enums with custom discriminant values
1423-
// Would result in ICE see the issue #92464 for more info
1421+
} else if tag.size(dl) == size {
1422+
// Make sure we only use scalar layout when the enum is entirely its
1423+
// own tag (i.e. it has no padding nor any non-ZST variant fields).
14241424
abi = Abi::Scalar(tag);
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} else {
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// Try to use a ScalarPair for all tagged enums.

‎src/test/ui/aligned_enum_cast.rs

+11-1
Original file line numberDiff line numberDiff line change
@@ -11,5 +11,15 @@ enum Aligned {
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fn main() {
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let aligned = Aligned::Zero;
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let fo = aligned as u8;
14-
println!("foo {}",fo);
14+
println!("foo {}", fo);
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assert_eq!(fo, 0);
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println!("{}", tou8(Aligned::Zero));
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assert_eq!(tou8(Aligned::Zero), 0);
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}
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#[inline(never)]
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fn tou8(al: Aligned) -> u8 {
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// Cast behind a function call so ConstProp does not see it
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// (so that we can test codegen).
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al as u8
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}

‎src/test/ui/layout/issue-96185-overaligned-enum.rs

+19
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,19 @@
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// normalize-stderr-test "pref: Align\([1-8] bytes\)" -> "pref: $$PREF_ALIGN"
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#![crate_type = "lib"]
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#![feature(rustc_attrs)]
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// This cannot use `Scalar` abi since there is padding.
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#[rustc_layout(debug)]
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#[repr(align(8))]
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pub enum Aligned1 { //~ ERROR: layout_of
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Zero = 0,
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One = 1,
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}
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// This should use `Scalar` abi.
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#[rustc_layout(debug)]
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#[repr(align(1))]
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pub enum Aligned2 { //~ ERROR: layout_of
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Zero = 0,
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One = 1,
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}

‎src/test/ui/layout/issue-96185-overaligned-enum.stderr

+172
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,172 @@
1+
error: layout_of(Aligned1) = Layout {
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fields: Arbitrary {
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offsets: [
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Size(0 bytes),
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],
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memory_index: [
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0,
8+
],
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},
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variants: Multiple {
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tag: Initialized {
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value: Int(
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I8,
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false,
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),
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valid_range: 0..=1,
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},
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tag_encoding: Direct,
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tag_field: 0,
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variants: [
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Layout {
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fields: Arbitrary {
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offsets: [],
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memory_index: [],
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},
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variants: Single {
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index: 0,
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},
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abi: Aggregate {
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sized: true,
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},
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largest_niche: None,
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align: AbiAndPrefAlign {
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abi: Align(8 bytes),
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pref: $PREF_ALIGN,
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},
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size: Size(8 bytes),
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},
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Layout {
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fields: Arbitrary {
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offsets: [],
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memory_index: [],
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},
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variants: Single {
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index: 1,
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},
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abi: Aggregate {
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sized: true,
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},
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largest_niche: None,
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align: AbiAndPrefAlign {
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abi: Align(8 bytes),
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pref: $PREF_ALIGN,
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},
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size: Size(8 bytes),
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},
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],
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},
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abi: Aggregate {
60+
sized: true,
61+
},
62+
largest_niche: Some(
63+
Niche {
64+
offset: Size(0 bytes),
65+
value: Int(
66+
I8,
67+
false,
68+
),
69+
valid_range: 0..=1,
70+
},
71+
),
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align: AbiAndPrefAlign {
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abi: Align(8 bytes),
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pref: $PREF_ALIGN,
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},
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size: Size(8 bytes),
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}
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--> $DIR/issue-96185-overaligned-enum.rs:8:1
79+
|
80+
LL | pub enum Aligned1 {
81+
| ^^^^^^^^^^^^^^^^^
82+
83+
error: layout_of(Aligned2) = Layout {
84+
fields: Arbitrary {
85+
offsets: [
86+
Size(0 bytes),
87+
],
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memory_index: [
89+
0,
90+
],
91+
},
92+
variants: Multiple {
93+
tag: Initialized {
94+
value: Int(
95+
I8,
96+
false,
97+
),
98+
valid_range: 0..=1,
99+
},
100+
tag_encoding: Direct,
101+
tag_field: 0,
102+
variants: [
103+
Layout {
104+
fields: Arbitrary {
105+
offsets: [],
106+
memory_index: [],
107+
},
108+
variants: Single {
109+
index: 0,
110+
},
111+
abi: Aggregate {
112+
sized: true,
113+
},
114+
largest_niche: None,
115+
align: AbiAndPrefAlign {
116+
abi: Align(1 bytes),
117+
pref: $PREF_ALIGN,
118+
},
119+
size: Size(1 bytes),
120+
},
121+
Layout {
122+
fields: Arbitrary {
123+
offsets: [],
124+
memory_index: [],
125+
},
126+
variants: Single {
127+
index: 1,
128+
},
129+
abi: Aggregate {
130+
sized: true,
131+
},
132+
largest_niche: None,
133+
align: AbiAndPrefAlign {
134+
abi: Align(1 bytes),
135+
pref: $PREF_ALIGN,
136+
},
137+
size: Size(1 bytes),
138+
},
139+
],
140+
},
141+
abi: Scalar(
142+
Initialized {
143+
value: Int(
144+
I8,
145+
false,
146+
),
147+
valid_range: 0..=1,
148+
},
149+
),
150+
largest_niche: Some(
151+
Niche {
152+
offset: Size(0 bytes),
153+
value: Int(
154+
I8,
155+
false,
156+
),
157+
valid_range: 0..=1,
158+
},
159+
),
160+
align: AbiAndPrefAlign {
161+
abi: Align(1 bytes),
162+
pref: $PREF_ALIGN,
163+
},
164+
size: Size(1 bytes),
165+
}
166+
--> $DIR/issue-96185-overaligned-enum.rs:16:1
167+
|
168+
LL | pub enum Aligned2 {
169+
| ^^^^^^^^^^^^^^^^^
170+
171+
error: aborting due to 2 previous errors
172+

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