1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
use std::fmt::Debug;
use std::iter;

use hir::def_id::DefId;
use rustc_hir as hir;
use rustc_index::bit_set::BitSet;
use rustc_index::{IndexSlice, IndexVec};
use rustc_middle::bug;
use rustc_middle::mir::{CoroutineLayout, CoroutineSavedLocal};
use rustc_middle::query::Providers;
use rustc_middle::ty::layout::{
    FloatExt, IntegerExt, LayoutCx, LayoutError, LayoutOf, TyAndLayout, MAX_SIMD_LANES,
};
use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_middle::ty::{
    self, AdtDef, CoroutineArgsExt, EarlyBinder, FieldDef, GenericArgsRef, Ty, TyCtxt,
    TypeVisitableExt,
};
use rustc_session::{DataTypeKind, FieldInfo, FieldKind, SizeKind, VariantInfo};
use rustc_span::sym;
use rustc_span::symbol::Symbol;
use rustc_target::abi::*;
use tracing::{debug, instrument, trace};

use crate::errors::{
    MultipleArrayFieldsSimdType, NonPrimitiveSimdType, OversizedSimdType, ZeroLengthSimdType,
};
use crate::layout_sanity_check::sanity_check_layout;

pub(crate) fn provide(providers: &mut Providers) {
    *providers = Providers { layout_of, ..*providers };
}

#[instrument(skip(tcx, query), level = "debug")]
fn layout_of<'tcx>(
    tcx: TyCtxt<'tcx>,
    query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
) -> Result<TyAndLayout<'tcx>, &'tcx LayoutError<'tcx>> {
    let (param_env, ty) = query.into_parts();
    debug!(?ty);

    // Optimization: We convert to RevealAll and convert opaque types in the where bounds
    // to their hidden types. This reduces overall uncached invocations of `layout_of` and
    // is thus a small performance improvement.
    let param_env = param_env.with_reveal_all_normalized(tcx);
    let unnormalized_ty = ty;

    // FIXME: We might want to have two different versions of `layout_of`:
    // One that can be called after typecheck has completed and can use
    // `normalize_erasing_regions` here and another one that can be called
    // before typecheck has completed and uses `try_normalize_erasing_regions`.
    let ty = match tcx.try_normalize_erasing_regions(param_env, ty) {
        Ok(t) => t,
        Err(normalization_error) => {
            return Err(tcx
                .arena
                .alloc(LayoutError::NormalizationFailure(ty, normalization_error)));
        }
    };

    if ty != unnormalized_ty {
        // Ensure this layout is also cached for the normalized type.
        return tcx.layout_of(param_env.and(ty));
    }

    let cx = LayoutCx { tcx, param_env };

    let layout = layout_of_uncached(&cx, ty)?;
    let layout = TyAndLayout { ty, layout };

    // If we are running with `-Zprint-type-sizes`, maybe record layouts
    // for dumping later.
    if cx.tcx.sess.opts.unstable_opts.print_type_sizes {
        record_layout_for_printing(&cx, layout);
    }

    sanity_check_layout(&cx, &layout);

    Ok(layout)
}

fn error<'tcx>(
    cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
    err: LayoutError<'tcx>,
) -> &'tcx LayoutError<'tcx> {
    cx.tcx.arena.alloc(err)
}

fn univariant_uninterned<'tcx>(
    cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
    ty: Ty<'tcx>,
    fields: &IndexSlice<FieldIdx, Layout<'_>>,
    repr: &ReprOptions,
    kind: StructKind,
) -> Result<LayoutS<FieldIdx, VariantIdx>, &'tcx LayoutError<'tcx>> {
    let dl = cx.data_layout();
    let pack = repr.pack;
    if pack.is_some() && repr.align.is_some() {
        cx.tcx.dcx().bug("struct cannot be packed and aligned");
    }

    cx.univariant(dl, fields, repr, kind).ok_or_else(|| error(cx, LayoutError::SizeOverflow(ty)))
}

fn layout_of_uncached<'tcx>(
    cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
    ty: Ty<'tcx>,
) -> Result<Layout<'tcx>, &'tcx LayoutError<'tcx>> {
    // Types that reference `ty::Error` pessimistically don't have a meaningful layout.
    // The only side-effect of this is possibly worse diagnostics in case the layout
    // was actually computable (like if the `ty::Error` showed up only in a `PhantomData`).
    if let Err(guar) = ty.error_reported() {
        return Err(error(cx, LayoutError::ReferencesError(guar)));
    }

    let tcx = cx.tcx;
    let param_env = cx.param_env;
    let dl = cx.data_layout();
    let scalar_unit = |value: Primitive| {
        let size = value.size(dl);
        assert!(size.bits() <= 128);
        Scalar::Initialized { value, valid_range: WrappingRange::full(size) }
    };
    let scalar = |value: Primitive| tcx.mk_layout(LayoutS::scalar(cx, scalar_unit(value)));

    let univariant = |fields: &IndexSlice<FieldIdx, Layout<'_>>, repr: &ReprOptions, kind| {
        Ok(tcx.mk_layout(univariant_uninterned(cx, ty, fields, repr, kind)?))
    };
    debug_assert!(!ty.has_non_region_infer());

    Ok(match *ty.kind() {
        ty::Pat(ty, pat) => {
            let layout = cx.layout_of(ty)?.layout;
            let mut layout = LayoutS::clone(&layout.0);
            match *pat {
                ty::PatternKind::Range { start, end, include_end } => {
                    if let Abi::Scalar(scalar) | Abi::ScalarPair(scalar, _) = &mut layout.abi {
                        if let Some(start) = start {
                            scalar.valid_range_mut().start = start
                                .try_eval_bits(tcx, param_env)
                                .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?;
                        }
                        if let Some(end) = end {
                            let mut end = end
                                .try_eval_bits(tcx, param_env)
                                .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?;
                            if !include_end {
                                end = end.wrapping_sub(1);
                            }
                            scalar.valid_range_mut().end = end;
                        }

                        let niche = Niche {
                            offset: Size::ZERO,
                            value: scalar.primitive(),
                            valid_range: scalar.valid_range(cx),
                        };

                        layout.largest_niche = Some(niche);

                        tcx.mk_layout(layout)
                    } else {
                        bug!("pattern type with range but not scalar layout: {ty:?}, {layout:?}")
                    }
                }
            }
        }

        // Basic scalars.
        ty::Bool => tcx.mk_layout(LayoutS::scalar(
            cx,
            Scalar::Initialized {
                value: Int(I8, false),
                valid_range: WrappingRange { start: 0, end: 1 },
            },
        )),
        ty::Char => tcx.mk_layout(LayoutS::scalar(
            cx,
            Scalar::Initialized {
                value: Int(I32, false),
                valid_range: WrappingRange { start: 0, end: 0x10FFFF },
            },
        )),
        ty::Int(ity) => scalar(Int(Integer::from_int_ty(dl, ity), true)),
        ty::Uint(ity) => scalar(Int(Integer::from_uint_ty(dl, ity), false)),
        ty::Float(fty) => scalar(Float(Float::from_float_ty(fty))),
        ty::FnPtr(..) => {
            let mut ptr = scalar_unit(Pointer(dl.instruction_address_space));
            ptr.valid_range_mut().start = 1;
            tcx.mk_layout(LayoutS::scalar(cx, ptr))
        }

        // The never type.
        ty::Never => tcx.mk_layout(cx.layout_of_never_type()),

        // Potentially-wide pointers.
        ty::Ref(_, pointee, _) | ty::RawPtr(pointee, _) => {
            let mut data_ptr = scalar_unit(Pointer(AddressSpace::DATA));
            if !ty.is_unsafe_ptr() {
                data_ptr.valid_range_mut().start = 1;
            }

            let pointee = tcx.normalize_erasing_regions(param_env, pointee);
            if pointee.is_sized(tcx, param_env) {
                return Ok(tcx.mk_layout(LayoutS::scalar(cx, data_ptr)));
            }

            let metadata = if let Some(metadata_def_id) = tcx.lang_items().metadata_type()
                // Projection eagerly bails out when the pointee references errors,
                // fall back to structurally deducing metadata.
                && !pointee.references_error()
            {
                let pointee_metadata = Ty::new_projection(tcx, metadata_def_id, [pointee]);
                let metadata_ty =
                    match tcx.try_normalize_erasing_regions(param_env, pointee_metadata) {
                        Ok(metadata_ty) => metadata_ty,
                        Err(mut err) => {
                            // Usually `<Ty as Pointee>::Metadata` can't be normalized because
                            // its struct tail cannot be normalized either, so try to get a
                            // more descriptive layout error here, which will lead to less confusing
                            // diagnostics.
                            //
                            // We use the raw struct tail function here to get the first tail
                            // that is an alias, which is likely the cause of the normalization
                            // error.
                            match tcx.try_normalize_erasing_regions(
                                param_env,
                                tcx.struct_tail_raw(pointee, |ty| ty, || {}),
                            ) {
                                Ok(_) => {}
                                Err(better_err) => {
                                    err = better_err;
                                }
                            }
                            return Err(error(cx, LayoutError::NormalizationFailure(pointee, err)));
                        }
                    };

                let metadata_layout = cx.layout_of(metadata_ty)?;
                // If the metadata is a 1-zst, then the pointer is thin.
                if metadata_layout.is_1zst() {
                    return Ok(tcx.mk_layout(LayoutS::scalar(cx, data_ptr)));
                }

                let Abi::Scalar(metadata) = metadata_layout.abi else {
                    return Err(error(cx, LayoutError::Unknown(pointee)));
                };

                metadata
            } else {
                let unsized_part = tcx.struct_tail_for_codegen(pointee, param_env);

                match unsized_part.kind() {
                    ty::Foreign(..) => {
                        return Ok(tcx.mk_layout(LayoutS::scalar(cx, data_ptr)));
                    }
                    ty::Slice(_) | ty::Str => scalar_unit(Int(dl.ptr_sized_integer(), false)),
                    ty::Dynamic(..) => {
                        let mut vtable = scalar_unit(Pointer(AddressSpace::DATA));
                        vtable.valid_range_mut().start = 1;
                        vtable
                    }
                    _ => {
                        return Err(error(cx, LayoutError::Unknown(pointee)));
                    }
                }
            };

            // Effectively a (ptr, meta) tuple.
            tcx.mk_layout(cx.scalar_pair(data_ptr, metadata))
        }

        ty::Dynamic(_, _, ty::DynStar) => {
            let mut data = scalar_unit(Pointer(AddressSpace::DATA));
            data.valid_range_mut().start = 0;
            let mut vtable = scalar_unit(Pointer(AddressSpace::DATA));
            vtable.valid_range_mut().start = 1;
            tcx.mk_layout(cx.scalar_pair(data, vtable))
        }

        // Arrays and slices.
        ty::Array(element, mut count) => {
            if count.has_aliases() {
                count = tcx.normalize_erasing_regions(param_env, count);
                if count.has_aliases() {
                    return Err(error(cx, LayoutError::Unknown(ty)));
                }
            }

            let count = count
                .try_eval_target_usize(tcx, param_env)
                .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?;
            let element = cx.layout_of(element)?;
            let size = element
                .size
                .checked_mul(count, dl)
                .ok_or_else(|| error(cx, LayoutError::SizeOverflow(ty)))?;

            let abi = if count != 0 && ty.is_privately_uninhabited(tcx, param_env) {
                Abi::Uninhabited
            } else {
                Abi::Aggregate { sized: true }
            };

            let largest_niche = if count != 0 { element.largest_niche } else { None };

            tcx.mk_layout(LayoutS {
                variants: Variants::Single { index: FIRST_VARIANT },
                fields: FieldsShape::Array { stride: element.size, count },
                abi,
                largest_niche,
                align: element.align,
                size,
                max_repr_align: None,
                unadjusted_abi_align: element.align.abi,
            })
        }
        ty::Slice(element) => {
            let element = cx.layout_of(element)?;
            tcx.mk_layout(LayoutS {
                variants: Variants::Single { index: FIRST_VARIANT },
                fields: FieldsShape::Array { stride: element.size, count: 0 },
                abi: Abi::Aggregate { sized: false },
                largest_niche: None,
                align: element.align,
                size: Size::ZERO,
                max_repr_align: None,
                unadjusted_abi_align: element.align.abi,
            })
        }
        ty::Str => tcx.mk_layout(LayoutS {
            variants: Variants::Single { index: FIRST_VARIANT },
            fields: FieldsShape::Array { stride: Size::from_bytes(1), count: 0 },
            abi: Abi::Aggregate { sized: false },
            largest_niche: None,
            align: dl.i8_align,
            size: Size::ZERO,
            max_repr_align: None,
            unadjusted_abi_align: dl.i8_align.abi,
        }),

        // Odd unit types.
        ty::FnDef(..) => {
            univariant(IndexSlice::empty(), &ReprOptions::default(), StructKind::AlwaysSized)?
        }
        ty::Dynamic(_, _, ty::Dyn) | ty::Foreign(..) => {
            let mut unit = univariant_uninterned(
                cx,
                ty,
                IndexSlice::empty(),
                &ReprOptions::default(),
                StructKind::AlwaysSized,
            )?;
            match unit.abi {
                Abi::Aggregate { ref mut sized } => *sized = false,
                _ => bug!(),
            }
            tcx.mk_layout(unit)
        }

        ty::Coroutine(def_id, args) => coroutine_layout(cx, ty, def_id, args)?,

        ty::Closure(_, args) => {
            let tys = args.as_closure().upvar_tys();
            univariant(
                &tys.iter()
                    .map(|ty| Ok(cx.layout_of(ty)?.layout))
                    .try_collect::<IndexVec<_, _>>()?,
                &ReprOptions::default(),
                StructKind::AlwaysSized,
            )?
        }

        ty::CoroutineClosure(_, args) => {
            let tys = args.as_coroutine_closure().upvar_tys();
            univariant(
                &tys.iter()
                    .map(|ty| Ok(cx.layout_of(ty)?.layout))
                    .try_collect::<IndexVec<_, _>>()?,
                &ReprOptions::default(),
                StructKind::AlwaysSized,
            )?
        }

        ty::Tuple(tys) => {
            let kind =
                if tys.len() == 0 { StructKind::AlwaysSized } else { StructKind::MaybeUnsized };

            univariant(
                &tys.iter().map(|k| Ok(cx.layout_of(k)?.layout)).try_collect::<IndexVec<_, _>>()?,
                &ReprOptions::default(),
                kind,
            )?
        }

        // SIMD vector types.
        ty::Adt(def, args) if def.repr().simd() => {
            if !def.is_struct() {
                // Should have yielded E0517 by now.
                tcx.dcx().delayed_bug("#[repr(simd)] was applied to an ADT that is not a struct");
                return Err(error(cx, LayoutError::Unknown(ty)));
            }

            let fields = &def.non_enum_variant().fields;

            // Supported SIMD vectors are homogeneous ADTs with at least one field:
            //
            // * #[repr(simd)] struct S(T, T, T, T);
            // * #[repr(simd)] struct S { x: T, y: T, z: T, w: T }
            // * #[repr(simd)] struct S([T; 4])
            //
            // where T is a primitive scalar (integer/float/pointer).

            // SIMD vectors with zero fields are not supported.
            // (should be caught by typeck)
            if fields.is_empty() {
                tcx.dcx().emit_fatal(ZeroLengthSimdType { ty })
            }

            // Type of the first ADT field:
            let f0_ty = fields[FieldIdx::ZERO].ty(tcx, args);

            // Heterogeneous SIMD vectors are not supported:
            // (should be caught by typeck)
            for fi in fields {
                if fi.ty(tcx, args) != f0_ty {
                    tcx.dcx().delayed_bug(
                        "#[repr(simd)] was applied to an ADT with heterogeneous field type",
                    );
                    return Err(error(cx, LayoutError::Unknown(ty)));
                }
            }

            // The element type and number of elements of the SIMD vector
            // are obtained from:
            //
            // * the element type and length of the single array field, if
            // the first field is of array type, or
            //
            // * the homogeneous field type and the number of fields.
            let (e_ty, e_len, is_array) = if let ty::Array(e_ty, _) = f0_ty.kind() {
                // First ADT field is an array:

                // SIMD vectors with multiple array fields are not supported:
                // Can't be caught by typeck with a generic simd type.
                if def.non_enum_variant().fields.len() != 1 {
                    tcx.dcx().emit_fatal(MultipleArrayFieldsSimdType { ty });
                }

                // Extract the number of elements from the layout of the array field:
                let FieldsShape::Array { count, .. } = cx.layout_of(f0_ty)?.layout.fields() else {
                    return Err(error(cx, LayoutError::Unknown(ty)));
                };

                (*e_ty, *count, true)
            } else {
                // First ADT field is not an array:
                (f0_ty, def.non_enum_variant().fields.len() as _, false)
            };

            // SIMD vectors of zero length are not supported.
            // Additionally, lengths are capped at 2^16 as a fixed maximum backends must
            // support.
            //
            // Can't be caught in typeck if the array length is generic.
            if e_len == 0 {
                tcx.dcx().emit_fatal(ZeroLengthSimdType { ty });
            } else if e_len > MAX_SIMD_LANES {
                tcx.dcx().emit_fatal(OversizedSimdType { ty, max_lanes: MAX_SIMD_LANES });
            }

            // Compute the ABI of the element type:
            let e_ly = cx.layout_of(e_ty)?;
            let Abi::Scalar(e_abi) = e_ly.abi else {
                // This error isn't caught in typeck, e.g., if
                // the element type of the vector is generic.
                tcx.dcx().emit_fatal(NonPrimitiveSimdType { ty, e_ty });
            };

            // Compute the size and alignment of the vector:
            let size = e_ly
                .size
                .checked_mul(e_len, dl)
                .ok_or_else(|| error(cx, LayoutError::SizeOverflow(ty)))?;

            let (abi, align) = if def.repr().packed() && !e_len.is_power_of_two() {
                // Non-power-of-two vectors have padding up to the next power-of-two.
                // If we're a packed repr, remove the padding while keeping the alignment as close
                // to a vector as possible.
                (
                    Abi::Aggregate { sized: true },
                    AbiAndPrefAlign {
                        abi: Align::max_for_offset(size),
                        pref: dl.vector_align(size).pref,
                    },
                )
            } else {
                (Abi::Vector { element: e_abi, count: e_len }, dl.vector_align(size))
            };
            let size = size.align_to(align.abi);

            // Compute the placement of the vector fields:
            let fields = if is_array {
                FieldsShape::Arbitrary { offsets: [Size::ZERO].into(), memory_index: [0].into() }
            } else {
                FieldsShape::Array { stride: e_ly.size, count: e_len }
            };

            tcx.mk_layout(LayoutS {
                variants: Variants::Single { index: FIRST_VARIANT },
                fields,
                abi,
                largest_niche: e_ly.largest_niche,
                size,
                align,
                max_repr_align: None,
                unadjusted_abi_align: align.abi,
            })
        }

        // ADTs.
        ty::Adt(def, args) => {
            // Cache the field layouts.
            let variants = def
                .variants()
                .iter()
                .map(|v| {
                    v.fields
                        .iter()
                        .map(|field| Ok(cx.layout_of(field.ty(tcx, args))?.layout))
                        .try_collect::<IndexVec<_, _>>()
                })
                .try_collect::<IndexVec<VariantIdx, _>>()?;

            if def.is_union() {
                if def.repr().pack.is_some() && def.repr().align.is_some() {
                    cx.tcx.dcx().span_delayed_bug(
                        tcx.def_span(def.did()),
                        "union cannot be packed and aligned",
                    );
                    return Err(error(cx, LayoutError::Unknown(ty)));
                }

                return Ok(tcx.mk_layout(
                    cx.layout_of_union(&def.repr(), &variants)
                        .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?,
                ));
            }

            let err_if_unsized = |field: &FieldDef, err_msg: &str| {
                let field_ty = tcx.type_of(field.did);
                let is_unsized = tcx
                    .try_instantiate_and_normalize_erasing_regions(args, cx.param_env, field_ty)
                    .map(|f| !f.is_sized(tcx, cx.param_env))
                    .map_err(|e| {
                        error(
                            cx,
                            LayoutError::NormalizationFailure(field_ty.instantiate_identity(), e),
                        )
                    })?;

                if is_unsized {
                    cx.tcx.dcx().span_delayed_bug(tcx.def_span(def.did()), err_msg.to_owned());
                    Err(error(cx, LayoutError::Unknown(ty)))
                } else {
                    Ok(())
                }
            };

            if def.is_struct() {
                if let Some((_, fields_except_last)) =
                    def.non_enum_variant().fields.raw.split_last()
                {
                    for f in fields_except_last {
                        err_if_unsized(f, "only the last field of a struct can be unsized")?;
                    }
                }
            } else {
                for f in def.all_fields() {
                    err_if_unsized(f, &format!("{}s cannot have unsized fields", def.descr()))?;
                }
            }

            let get_discriminant_type =
                |min, max| Integer::repr_discr(tcx, ty, &def.repr(), min, max);

            let discriminants_iter = || {
                def.is_enum()
                    .then(|| def.discriminants(tcx).map(|(v, d)| (v, d.val as i128)))
                    .into_iter()
                    .flatten()
            };

            let dont_niche_optimize_enum = def.repr().inhibit_enum_layout_opt()
                || def
                    .variants()
                    .iter_enumerated()
                    .any(|(i, v)| v.discr != ty::VariantDiscr::Relative(i.as_u32()));

            let maybe_unsized = def.is_struct()
                && def.non_enum_variant().tail_opt().is_some_and(|last_field| {
                    let param_env = tcx.param_env(def.did());
                    !tcx.type_of(last_field.did).instantiate_identity().is_sized(tcx, param_env)
                });

            let Some(layout) = cx.layout_of_struct_or_enum(
                &def.repr(),
                &variants,
                def.is_enum(),
                def.is_unsafe_cell(),
                tcx.layout_scalar_valid_range(def.did()),
                get_discriminant_type,
                discriminants_iter(),
                dont_niche_optimize_enum,
                !maybe_unsized,
            ) else {
                return Err(error(cx, LayoutError::SizeOverflow(ty)));
            };

            // If the struct tail is sized and can be unsized, check that unsizing doesn't move the fields around.
            if cfg!(debug_assertions)
                && maybe_unsized
                && def.non_enum_variant().tail().ty(tcx, args).is_sized(tcx, cx.param_env)
            {
                let mut variants = variants;
                let tail_replacement = cx.layout_of(Ty::new_slice(tcx, tcx.types.u8)).unwrap();
                *variants[FIRST_VARIANT].raw.last_mut().unwrap() = tail_replacement.layout;

                let Some(unsized_layout) = cx.layout_of_struct_or_enum(
                    &def.repr(),
                    &variants,
                    def.is_enum(),
                    def.is_unsafe_cell(),
                    tcx.layout_scalar_valid_range(def.did()),
                    get_discriminant_type,
                    discriminants_iter(),
                    dont_niche_optimize_enum,
                    !maybe_unsized,
                ) else {
                    bug!("failed to compute unsized layout of {ty:?}");
                };

                let FieldsShape::Arbitrary { offsets: sized_offsets, .. } = &layout.fields else {
                    bug!("unexpected FieldsShape for sized layout of {ty:?}: {:?}", layout.fields);
                };
                let FieldsShape::Arbitrary { offsets: unsized_offsets, .. } =
                    &unsized_layout.fields
                else {
                    bug!(
                        "unexpected FieldsShape for unsized layout of {ty:?}: {:?}",
                        unsized_layout.fields
                    );
                };

                let (sized_tail, sized_fields) = sized_offsets.raw.split_last().unwrap();
                let (unsized_tail, unsized_fields) = unsized_offsets.raw.split_last().unwrap();

                if sized_fields != unsized_fields {
                    bug!("unsizing {ty:?} changed field order!\n{layout:?}\n{unsized_layout:?}");
                }

                if sized_tail < unsized_tail {
                    bug!("unsizing {ty:?} moved tail backwards!\n{layout:?}\n{unsized_layout:?}");
                }
            }

            tcx.mk_layout(layout)
        }

        // Types with no meaningful known layout.
        ty::Alias(..) => {
            // NOTE(eddyb) `layout_of` query should've normalized these away,
            // if that was possible, so there's no reason to try again here.
            return Err(error(cx, LayoutError::Unknown(ty)));
        }

        ty::Bound(..) | ty::CoroutineWitness(..) | ty::Infer(_) | ty::Error(_) => {
            bug!("Layout::compute: unexpected type `{}`", ty)
        }

        ty::Placeholder(..) | ty::Param(_) => {
            return Err(error(cx, LayoutError::Unknown(ty)));
        }
    })
}

/// Overlap eligibility and variant assignment for each CoroutineSavedLocal.
#[derive(Clone, Debug, PartialEq)]
enum SavedLocalEligibility {
    Unassigned,
    Assigned(VariantIdx),
    Ineligible(Option<FieldIdx>),
}

// When laying out coroutines, we divide our saved local fields into two
// categories: overlap-eligible and overlap-ineligible.
//
// Those fields which are ineligible for overlap go in a "prefix" at the
// beginning of the layout, and always have space reserved for them.
//
// Overlap-eligible fields are only assigned to one variant, so we lay
// those fields out for each variant and put them right after the
// prefix.
//
// Finally, in the layout details, we point to the fields from the
// variants they are assigned to. It is possible for some fields to be
// included in multiple variants. No field ever "moves around" in the
// layout; its offset is always the same.
//
// Also included in the layout are the upvars and the discriminant.
// These are included as fields on the "outer" layout; they are not part
// of any variant.

/// Compute the eligibility and assignment of each local.
fn coroutine_saved_local_eligibility(
    info: &CoroutineLayout<'_>,
) -> (BitSet<CoroutineSavedLocal>, IndexVec<CoroutineSavedLocal, SavedLocalEligibility>) {
    use SavedLocalEligibility::*;

    let mut assignments: IndexVec<CoroutineSavedLocal, SavedLocalEligibility> =
        IndexVec::from_elem(Unassigned, &info.field_tys);

    // The saved locals not eligible for overlap. These will get
    // "promoted" to the prefix of our coroutine.
    let mut ineligible_locals = BitSet::new_empty(info.field_tys.len());

    // Figure out which of our saved locals are fields in only
    // one variant. The rest are deemed ineligible for overlap.
    for (variant_index, fields) in info.variant_fields.iter_enumerated() {
        for local in fields {
            match assignments[*local] {
                Unassigned => {
                    assignments[*local] = Assigned(variant_index);
                }
                Assigned(idx) => {
                    // We've already seen this local at another suspension
                    // point, so it is no longer a candidate.
                    trace!(
                        "removing local {:?} in >1 variant ({:?}, {:?})",
                        local, variant_index, idx
                    );
                    ineligible_locals.insert(*local);
                    assignments[*local] = Ineligible(None);
                }
                Ineligible(_) => {}
            }
        }
    }

    // Next, check every pair of eligible locals to see if they
    // conflict.
    for local_a in info.storage_conflicts.rows() {
        let conflicts_a = info.storage_conflicts.count(local_a);
        if ineligible_locals.contains(local_a) {
            continue;
        }

        for local_b in info.storage_conflicts.iter(local_a) {
            // local_a and local_b are storage live at the same time, therefore they
            // cannot overlap in the coroutine layout. The only way to guarantee
            // this is if they are in the same variant, or one is ineligible
            // (which means it is stored in every variant).
            if ineligible_locals.contains(local_b) || assignments[local_a] == assignments[local_b] {
                continue;
            }

            // If they conflict, we will choose one to make ineligible.
            // This is not always optimal; it's just a greedy heuristic that
            // seems to produce good results most of the time.
            let conflicts_b = info.storage_conflicts.count(local_b);
            let (remove, other) =
                if conflicts_a > conflicts_b { (local_a, local_b) } else { (local_b, local_a) };
            ineligible_locals.insert(remove);
            assignments[remove] = Ineligible(None);
            trace!("removing local {:?} due to conflict with {:?}", remove, other);
        }
    }

    // Count the number of variants in use. If only one of them, then it is
    // impossible to overlap any locals in our layout. In this case it's
    // always better to make the remaining locals ineligible, so we can
    // lay them out with the other locals in the prefix and eliminate
    // unnecessary padding bytes.
    {
        let mut used_variants = BitSet::new_empty(info.variant_fields.len());
        for assignment in &assignments {
            if let Assigned(idx) = assignment {
                used_variants.insert(*idx);
            }
        }
        if used_variants.count() < 2 {
            for assignment in assignments.iter_mut() {
                *assignment = Ineligible(None);
            }
            ineligible_locals.insert_all();
        }
    }

    // Write down the order of our locals that will be promoted to the prefix.
    {
        for (idx, local) in ineligible_locals.iter().enumerate() {
            assignments[local] = Ineligible(Some(FieldIdx::from_usize(idx)));
        }
    }
    debug!("coroutine saved local assignments: {:?}", assignments);

    (ineligible_locals, assignments)
}

/// Compute the full coroutine layout.
fn coroutine_layout<'tcx>(
    cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
    ty: Ty<'tcx>,
    def_id: hir::def_id::DefId,
    args: GenericArgsRef<'tcx>,
) -> Result<Layout<'tcx>, &'tcx LayoutError<'tcx>> {
    use SavedLocalEligibility::*;
    let tcx = cx.tcx;
    let instantiate_field = |ty: Ty<'tcx>| EarlyBinder::bind(ty).instantiate(tcx, args);

    let Some(info) = tcx.coroutine_layout(def_id, args.as_coroutine().kind_ty()) else {
        return Err(error(cx, LayoutError::Unknown(ty)));
    };
    let (ineligible_locals, assignments) = coroutine_saved_local_eligibility(info);

    // Build a prefix layout, including "promoting" all ineligible
    // locals as part of the prefix. We compute the layout of all of
    // these fields at once to get optimal packing.
    let tag_index = args.as_coroutine().prefix_tys().len();

    // `info.variant_fields` already accounts for the reserved variants, so no need to add them.
    let max_discr = (info.variant_fields.len() - 1) as u128;
    let discr_int = Integer::fit_unsigned(max_discr);
    let tag = Scalar::Initialized {
        value: Primitive::Int(discr_int, false),
        valid_range: WrappingRange { start: 0, end: max_discr },
    };
    let tag_layout = cx.tcx.mk_layout(LayoutS::scalar(cx, tag));

    let promoted_layouts = ineligible_locals.iter().map(|local| {
        let field_ty = instantiate_field(info.field_tys[local].ty);
        let uninit_ty = Ty::new_maybe_uninit(tcx, field_ty);
        Ok(cx.spanned_layout_of(uninit_ty, info.field_tys[local].source_info.span)?.layout)
    });
    let prefix_layouts = args
        .as_coroutine()
        .prefix_tys()
        .iter()
        .map(|ty| Ok(cx.layout_of(ty)?.layout))
        .chain(iter::once(Ok(tag_layout)))
        .chain(promoted_layouts)
        .try_collect::<IndexVec<_, _>>()?;
    let prefix = univariant_uninterned(
        cx,
        ty,
        &prefix_layouts,
        &ReprOptions::default(),
        StructKind::AlwaysSized,
    )?;

    let (prefix_size, prefix_align) = (prefix.size, prefix.align);

    // Split the prefix layout into the "outer" fields (upvars and
    // discriminant) and the "promoted" fields. Promoted fields will
    // get included in each variant that requested them in
    // CoroutineLayout.
    debug!("prefix = {:#?}", prefix);
    let (outer_fields, promoted_offsets, promoted_memory_index) = match prefix.fields {
        FieldsShape::Arbitrary { mut offsets, memory_index } => {
            let mut inverse_memory_index = memory_index.invert_bijective_mapping();

            // "a" (`0..b_start`) and "b" (`b_start..`) correspond to
            // "outer" and "promoted" fields respectively.
            let b_start = FieldIdx::from_usize(tag_index + 1);
            let offsets_b = IndexVec::from_raw(offsets.raw.split_off(b_start.as_usize()));
            let offsets_a = offsets;

            // Disentangle the "a" and "b" components of `inverse_memory_index`
            // by preserving the order but keeping only one disjoint "half" each.
            // FIXME(eddyb) build a better abstraction for permutations, if possible.
            let inverse_memory_index_b: IndexVec<u32, FieldIdx> = inverse_memory_index
                .iter()
                .filter_map(|&i| i.as_u32().checked_sub(b_start.as_u32()).map(FieldIdx::from_u32))
                .collect();
            inverse_memory_index.raw.retain(|&i| i < b_start);
            let inverse_memory_index_a = inverse_memory_index;

            // Since `inverse_memory_index_{a,b}` each only refer to their
            // respective fields, they can be safely inverted
            let memory_index_a = inverse_memory_index_a.invert_bijective_mapping();
            let memory_index_b = inverse_memory_index_b.invert_bijective_mapping();

            let outer_fields =
                FieldsShape::Arbitrary { offsets: offsets_a, memory_index: memory_index_a };
            (outer_fields, offsets_b, memory_index_b)
        }
        _ => bug!(),
    };

    let mut size = prefix.size;
    let mut align = prefix.align;
    let variants = info
        .variant_fields
        .iter_enumerated()
        .map(|(index, variant_fields)| {
            // Only include overlap-eligible fields when we compute our variant layout.
            let variant_only_tys = variant_fields
                .iter()
                .filter(|local| match assignments[**local] {
                    Unassigned => bug!(),
                    Assigned(v) if v == index => true,
                    Assigned(_) => bug!("assignment does not match variant"),
                    Ineligible(_) => false,
                })
                .map(|local| {
                    let field_ty = instantiate_field(info.field_tys[*local].ty);
                    Ty::new_maybe_uninit(tcx, field_ty)
                });

            let mut variant = univariant_uninterned(
                cx,
                ty,
                &variant_only_tys
                    .map(|ty| Ok(cx.layout_of(ty)?.layout))
                    .try_collect::<IndexVec<_, _>>()?,
                &ReprOptions::default(),
                StructKind::Prefixed(prefix_size, prefix_align.abi),
            )?;
            variant.variants = Variants::Single { index };

            let FieldsShape::Arbitrary { offsets, memory_index } = variant.fields else {
                bug!();
            };

            // Now, stitch the promoted and variant-only fields back together in
            // the order they are mentioned by our CoroutineLayout.
            // Because we only use some subset (that can differ between variants)
            // of the promoted fields, we can't just pick those elements of the
            // `promoted_memory_index` (as we'd end up with gaps).
            // So instead, we build an "inverse memory_index", as if all of the
            // promoted fields were being used, but leave the elements not in the
            // subset as `INVALID_FIELD_IDX`, which we can filter out later to
            // obtain a valid (bijective) mapping.
            const INVALID_FIELD_IDX: FieldIdx = FieldIdx::MAX;
            debug_assert!(variant_fields.next_index() <= INVALID_FIELD_IDX);

            let mut combined_inverse_memory_index = IndexVec::from_elem_n(
                INVALID_FIELD_IDX,
                promoted_memory_index.len() + memory_index.len(),
            );
            let mut offsets_and_memory_index = iter::zip(offsets, memory_index);
            let combined_offsets = variant_fields
                .iter_enumerated()
                .map(|(i, local)| {
                    let (offset, memory_index) = match assignments[*local] {
                        Unassigned => bug!(),
                        Assigned(_) => {
                            let (offset, memory_index) = offsets_and_memory_index.next().unwrap();
                            (offset, promoted_memory_index.len() as u32 + memory_index)
                        }
                        Ineligible(field_idx) => {
                            let field_idx = field_idx.unwrap();
                            (promoted_offsets[field_idx], promoted_memory_index[field_idx])
                        }
                    };
                    combined_inverse_memory_index[memory_index] = i;
                    offset
                })
                .collect();

            // Remove the unused slots and invert the mapping to obtain the
            // combined `memory_index` (also see previous comment).
            combined_inverse_memory_index.raw.retain(|&i| i != INVALID_FIELD_IDX);
            let combined_memory_index = combined_inverse_memory_index.invert_bijective_mapping();

            variant.fields = FieldsShape::Arbitrary {
                offsets: combined_offsets,
                memory_index: combined_memory_index,
            };

            size = size.max(variant.size);
            align = align.max(variant.align);
            Ok(variant)
        })
        .try_collect::<IndexVec<VariantIdx, _>>()?;

    size = size.align_to(align.abi);

    let abi = if prefix.abi.is_uninhabited() || variants.iter().all(|v| v.abi.is_uninhabited()) {
        Abi::Uninhabited
    } else {
        Abi::Aggregate { sized: true }
    };

    let layout = tcx.mk_layout(LayoutS {
        variants: Variants::Multiple {
            tag,
            tag_encoding: TagEncoding::Direct,
            tag_field: tag_index,
            variants,
        },
        fields: outer_fields,
        abi,
        largest_niche: prefix.largest_niche,
        size,
        align,
        max_repr_align: None,
        unadjusted_abi_align: align.abi,
    });
    debug!("coroutine layout ({:?}): {:#?}", ty, layout);
    Ok(layout)
}

fn record_layout_for_printing<'tcx>(cx: &LayoutCx<'tcx, TyCtxt<'tcx>>, layout: TyAndLayout<'tcx>) {
    // Ignore layouts that are done with non-empty environments or
    // non-monomorphic layouts, as the user only wants to see the stuff
    // resulting from the final codegen session.
    if layout.ty.has_non_region_param() || !cx.param_env.caller_bounds().is_empty() {
        return;
    }

    // (delay format until we actually need it)
    let record = |kind, packed, opt_discr_size, variants| {
        let type_desc = with_no_trimmed_paths!(format!("{}", layout.ty));
        cx.tcx.sess.code_stats.record_type_size(
            kind,
            type_desc,
            layout.align.abi,
            layout.size,
            packed,
            opt_discr_size,
            variants,
        );
    };

    match *layout.ty.kind() {
        ty::Adt(adt_def, _) => {
            debug!("print-type-size t: `{:?}` process adt", layout.ty);
            let adt_kind = adt_def.adt_kind();
            let adt_packed = adt_def.repr().pack.is_some();
            let (variant_infos, opt_discr_size) = variant_info_for_adt(cx, layout, adt_def);
            record(adt_kind.into(), adt_packed, opt_discr_size, variant_infos);
        }

        ty::Coroutine(def_id, args) => {
            debug!("print-type-size t: `{:?}` record coroutine", layout.ty);
            // Coroutines always have a begin/poisoned/end state with additional suspend points
            let (variant_infos, opt_discr_size) =
                variant_info_for_coroutine(cx, layout, def_id, args);
            record(DataTypeKind::Coroutine, false, opt_discr_size, variant_infos);
        }

        ty::Closure(..) => {
            debug!("print-type-size t: `{:?}` record closure", layout.ty);
            record(DataTypeKind::Closure, false, None, vec![]);
        }

        _ => {
            debug!("print-type-size t: `{:?}` skip non-nominal", layout.ty);
        }
    };
}

fn variant_info_for_adt<'tcx>(
    cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
    layout: TyAndLayout<'tcx>,
    adt_def: AdtDef<'tcx>,
) -> (Vec<VariantInfo>, Option<Size>) {
    let build_variant_info = |n: Option<Symbol>, flds: &[Symbol], layout: TyAndLayout<'tcx>| {
        let mut min_size = Size::ZERO;
        let field_info: Vec<_> = flds
            .iter()
            .enumerate()
            .map(|(i, &name)| {
                let field_layout = layout.field(cx, i);
                let offset = layout.fields.offset(i);
                min_size = min_size.max(offset + field_layout.size);
                FieldInfo {
                    kind: FieldKind::AdtField,
                    name,
                    offset: offset.bytes(),
                    size: field_layout.size.bytes(),
                    align: field_layout.align.abi.bytes(),
                    type_name: None,
                }
            })
            .collect();

        VariantInfo {
            name: n,
            kind: if layout.is_unsized() { SizeKind::Min } else { SizeKind::Exact },
            align: layout.align.abi.bytes(),
            size: if min_size.bytes() == 0 { layout.size.bytes() } else { min_size.bytes() },
            fields: field_info,
        }
    };

    match layout.variants {
        Variants::Single { index } => {
            if !adt_def.variants().is_empty() && layout.fields != FieldsShape::Primitive {
                debug!("print-type-size `{:#?}` variant {}", layout, adt_def.variant(index).name);
                let variant_def = &adt_def.variant(index);
                let fields: Vec<_> = variant_def.fields.iter().map(|f| f.name).collect();
                (vec![build_variant_info(Some(variant_def.name), &fields, layout)], None)
            } else {
                (vec![], None)
            }
        }

        Variants::Multiple { tag, ref tag_encoding, .. } => {
            debug!(
                "print-type-size `{:#?}` adt general variants def {}",
                layout.ty,
                adt_def.variants().len()
            );
            let variant_infos: Vec<_> = adt_def
                .variants()
                .iter_enumerated()
                .map(|(i, variant_def)| {
                    let fields: Vec<_> = variant_def.fields.iter().map(|f| f.name).collect();
                    build_variant_info(Some(variant_def.name), &fields, layout.for_variant(cx, i))
                })
                .collect();

            (
                variant_infos,
                match tag_encoding {
                    TagEncoding::Direct => Some(tag.size(cx)),
                    _ => None,
                },
            )
        }
    }
}

fn variant_info_for_coroutine<'tcx>(
    cx: &LayoutCx<'tcx, TyCtxt<'tcx>>,
    layout: TyAndLayout<'tcx>,
    def_id: DefId,
    args: ty::GenericArgsRef<'tcx>,
) -> (Vec<VariantInfo>, Option<Size>) {
    use itertools::Itertools;

    let Variants::Multiple { tag, ref tag_encoding, tag_field, .. } = layout.variants else {
        return (vec![], None);
    };

    let coroutine = cx.tcx.coroutine_layout(def_id, args.as_coroutine().kind_ty()).unwrap();
    let upvar_names = cx.tcx.closure_saved_names_of_captured_variables(def_id);

    let mut upvars_size = Size::ZERO;
    let upvar_fields: Vec<_> = args
        .as_coroutine()
        .upvar_tys()
        .iter()
        .zip_eq(upvar_names)
        .enumerate()
        .map(|(field_idx, (_, name))| {
            let field_layout = layout.field(cx, field_idx);
            let offset = layout.fields.offset(field_idx);
            upvars_size = upvars_size.max(offset + field_layout.size);
            FieldInfo {
                kind: FieldKind::Upvar,
                name: *name,
                offset: offset.bytes(),
                size: field_layout.size.bytes(),
                align: field_layout.align.abi.bytes(),
                type_name: None,
            }
        })
        .collect();

    let mut variant_infos: Vec<_> = coroutine
        .variant_fields
        .iter_enumerated()
        .map(|(variant_idx, variant_def)| {
            let variant_layout = layout.for_variant(cx, variant_idx);
            let mut variant_size = Size::ZERO;
            let fields = variant_def
                .iter()
                .enumerate()
                .map(|(field_idx, local)| {
                    let field_name = coroutine.field_names[*local];
                    let field_layout = variant_layout.field(cx, field_idx);
                    let offset = variant_layout.fields.offset(field_idx);
                    // The struct is as large as the last field's end
                    variant_size = variant_size.max(offset + field_layout.size);
                    FieldInfo {
                        kind: FieldKind::CoroutineLocal,
                        name: field_name.unwrap_or(Symbol::intern(&format!(
                            ".coroutine_field{}",
                            local.as_usize()
                        ))),
                        offset: offset.bytes(),
                        size: field_layout.size.bytes(),
                        align: field_layout.align.abi.bytes(),
                        // Include the type name if there is no field name, or if the name is the
                        // __awaitee placeholder symbol which means a child future being `.await`ed.
                        type_name: (field_name.is_none() || field_name == Some(sym::__awaitee))
                            .then(|| Symbol::intern(&field_layout.ty.to_string())),
                    }
                })
                .chain(upvar_fields.iter().copied())
                .collect();

            // If the variant has no state-specific fields, then it's the size of the upvars.
            if variant_size == Size::ZERO {
                variant_size = upvars_size;
            }

            // This `if` deserves some explanation.
            //
            // The layout code has a choice of where to place the discriminant of this coroutine.
            // If the discriminant of the coroutine is placed early in the layout (before the
            // variant's own fields), then it'll implicitly be counted towards the size of the
            // variant, since we use the maximum offset to calculate size.
            //    (side-note: I know this is a bit problematic given upvars placement, etc).
            //
            // This is important, since the layout printing code always subtracts this discriminant
            // size from the variant size if the struct is "enum"-like, so failing to account for it
            // will either lead to numerical underflow, or an underreported variant size...
            //
            // However, if the discriminant is placed past the end of the variant, then we need
            // to factor in the size of the discriminant manually. This really should be refactored
            // better, but this "works" for now.
            if layout.fields.offset(tag_field) >= variant_size {
                variant_size += match tag_encoding {
                    TagEncoding::Direct => tag.size(cx),
                    _ => Size::ZERO,
                };
            }

            VariantInfo {
                name: Some(Symbol::intern(&ty::CoroutineArgs::variant_name(variant_idx))),
                kind: SizeKind::Exact,
                size: variant_size.bytes(),
                align: variant_layout.align.abi.bytes(),
                fields,
            }
        })
        .collect();

    // The first three variants are hardcoded to be `UNRESUMED`, `RETURNED` and `POISONED`.
    // We will move the `RETURNED` and `POISONED` elements to the end so we
    // are left with a sorting order according to the coroutines yield points:
    // First `Unresumed`, then the `SuspendN` followed by `Returned` and `Panicked` (POISONED).
    let end_states = variant_infos.drain(1..=2);
    let end_states: Vec<_> = end_states.collect();
    variant_infos.extend(end_states);

    (
        variant_infos,
        match tag_encoding {
            TagEncoding::Direct => Some(tag.size(cx)),
            _ => None,
        },
    )
}