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
pub use Integer::*;
pub use Primitive::*;

use crate::spec::Target;

use std::convert::{TryFrom, TryInto};
use std::num::NonZeroUsize;
use std::ops::{Add, AddAssign, Deref, Mul, Range, RangeInclusive, Sub};

use rustc_index::vec::{Idx, IndexVec};
use rustc_macros::HashStable_Generic;
use rustc_span::Span;

pub mod call;

/// Parsed [Data layout](http://llvm.org/docs/LangRef.html#data-layout)
/// for a target, which contains everything needed to compute layouts.
pub struct TargetDataLayout {
    pub endian: Endian,
    pub i1_align: AbiAndPrefAlign,
    pub i8_align: AbiAndPrefAlign,
    pub i16_align: AbiAndPrefAlign,
    pub i32_align: AbiAndPrefAlign,
    pub i64_align: AbiAndPrefAlign,
    pub i128_align: AbiAndPrefAlign,
    pub f32_align: AbiAndPrefAlign,
    pub f64_align: AbiAndPrefAlign,
    pub pointer_size: Size,
    pub pointer_align: AbiAndPrefAlign,
    pub aggregate_align: AbiAndPrefAlign,

    /// Alignments for vector types.
    pub vector_align: Vec<(Size, AbiAndPrefAlign)>,

    pub instruction_address_space: AddressSpace,
}

impl Default for TargetDataLayout {
    /// Creates an instance of `TargetDataLayout`.
    fn default() -> TargetDataLayout {
        let align = |bits| Align::from_bits(bits).unwrap();
        TargetDataLayout {
            endian: Endian::Big,
            i1_align: AbiAndPrefAlign::new(align(8)),
            i8_align: AbiAndPrefAlign::new(align(8)),
            i16_align: AbiAndPrefAlign::new(align(16)),
            i32_align: AbiAndPrefAlign::new(align(32)),
            i64_align: AbiAndPrefAlign { abi: align(32), pref: align(64) },
            i128_align: AbiAndPrefAlign { abi: align(32), pref: align(64) },
            f32_align: AbiAndPrefAlign::new(align(32)),
            f64_align: AbiAndPrefAlign::new(align(64)),
            pointer_size: Size::from_bits(64),
            pointer_align: AbiAndPrefAlign::new(align(64)),
            aggregate_align: AbiAndPrefAlign { abi: align(0), pref: align(64) },
            vector_align: vec![
                (Size::from_bits(64), AbiAndPrefAlign::new(align(64))),
                (Size::from_bits(128), AbiAndPrefAlign::new(align(128))),
            ],
            instruction_address_space: AddressSpace::DATA,
        }
    }
}

impl TargetDataLayout {
    pub fn parse(target: &Target) -> Result<TargetDataLayout, String> {
        // Parse an address space index from a string.
        let parse_address_space = |s: &str, cause: &str| {
            s.parse::<u32>().map(AddressSpace).map_err(|err| {
                format!("invalid address space `{}` for `{}` in \"data-layout\": {}", s, cause, err)
            })
        };

        // Parse a bit count from a string.
        let parse_bits = |s: &str, kind: &str, cause: &str| {
            s.parse::<u64>().map_err(|err| {
                format!("invalid {} `{}` for `{}` in \"data-layout\": {}", kind, s, cause, err)
            })
        };

        // Parse a size string.
        let size = |s: &str, cause: &str| parse_bits(s, "size", cause).map(Size::from_bits);

        // Parse an alignment string.
        let align = |s: &[&str], cause: &str| {
            if s.is_empty() {
                return Err(format!("missing alignment for `{}` in \"data-layout\"", cause));
            }
            let align_from_bits = |bits| {
                Align::from_bits(bits).map_err(|err| {
                    format!("invalid alignment for `{}` in \"data-layout\": {}", cause, err)
                })
            };
            let abi = parse_bits(s[0], "alignment", cause)?;
            let pref = s.get(1).map_or(Ok(abi), |pref| parse_bits(pref, "alignment", cause))?;
            Ok(AbiAndPrefAlign { abi: align_from_bits(abi)?, pref: align_from_bits(pref)? })
        };

        let mut dl = TargetDataLayout::default();
        let mut i128_align_src = 64;
        for spec in target.data_layout.split('-') {
            let spec_parts = spec.split(':').collect::<Vec<_>>();

            match &*spec_parts {
                ["e"] => dl.endian = Endian::Little,
                ["E"] => dl.endian = Endian::Big,
                [p] if p.starts_with('P') => {
                    dl.instruction_address_space = parse_address_space(&p[1..], "P")?
                }
                ["a", ref a @ ..] => dl.aggregate_align = align(a, "a")?,
                ["f32", ref a @ ..] => dl.f32_align = align(a, "f32")?,
                ["f64", ref a @ ..] => dl.f64_align = align(a, "f64")?,
                [p @ "p", s, ref a @ ..] | [p @ "p0", s, ref a @ ..] => {
                    dl.pointer_size = size(s, p)?;
                    dl.pointer_align = align(a, p)?;
                }
                [s, ref a @ ..] if s.starts_with('i') => {
                    let bits = match s[1..].parse::<u64>() {
                        Ok(bits) => bits,
                        Err(_) => {
                            size(&s[1..], "i")?; // For the user error.
                            continue;
                        }
                    };
                    let a = align(a, s)?;
                    match bits {
                        1 => dl.i1_align = a,
                        8 => dl.i8_align = a,
                        16 => dl.i16_align = a,
                        32 => dl.i32_align = a,
                        64 => dl.i64_align = a,
                        _ => {}
                    }
                    if bits >= i128_align_src && bits <= 128 {
                        // Default alignment for i128 is decided by taking the alignment of
                        // largest-sized i{64..=128}.
                        i128_align_src = bits;
                        dl.i128_align = a;
                    }
                }
                [s, ref a @ ..] if s.starts_with('v') => {
                    let v_size = size(&s[1..], "v")?;
                    let a = align(a, s)?;
                    if let Some(v) = dl.vector_align.iter_mut().find(|v| v.0 == v_size) {
                        v.1 = a;
                        continue;
                    }
                    // No existing entry, add a new one.
                    dl.vector_align.push((v_size, a));
                }
                _ => {} // Ignore everything else.
            }
        }

        // Perform consistency checks against the Target information.
        let endian_str = match dl.endian {
            Endian::Little => "little",
            Endian::Big => "big",
        };
        if endian_str != target.target_endian {
            return Err(format!(
                "inconsistent target specification: \"data-layout\" claims \
                                architecture is {}-endian, while \"target-endian\" is `{}`",
                endian_str, target.target_endian
            ));
        }

        if dl.pointer_size.bits().to_string() != target.target_pointer_width {
            return Err(format!(
                "inconsistent target specification: \"data-layout\" claims \
                                pointers are {}-bit, while \"target-pointer-width\" is `{}`",
                dl.pointer_size.bits(),
                target.target_pointer_width
            ));
        }

        Ok(dl)
    }

    /// Returns exclusive upper bound on object size.
    ///
    /// The theoretical maximum object size is defined as the maximum positive `isize` value.
    /// This ensures that the `offset` semantics remain well-defined by allowing it to correctly
    /// index every address within an object along with one byte past the end, along with allowing
    /// `isize` to store the difference between any two pointers into an object.
    ///
    /// The upper bound on 64-bit currently needs to be lower because LLVM uses a 64-bit integer
    /// to represent object size in bits. It would need to be 1 << 61 to account for this, but is
    /// currently conservatively bounded to 1 << 47 as that is enough to cover the current usable
    /// address space on 64-bit ARMv8 and x86_64.
    pub fn obj_size_bound(&self) -> u64 {
        match self.pointer_size.bits() {
            16 => 1 << 15,
            32 => 1 << 31,
            64 => 1 << 47,
            bits => panic!("obj_size_bound: unknown pointer bit size {}", bits),
        }
    }

    pub fn ptr_sized_integer(&self) -> Integer {
        match self.pointer_size.bits() {
            16 => I16,
            32 => I32,
            64 => I64,
            bits => panic!("ptr_sized_integer: unknown pointer bit size {}", bits),
        }
    }

    pub fn vector_align(&self, vec_size: Size) -> AbiAndPrefAlign {
        for &(size, align) in &self.vector_align {
            if size == vec_size {
                return align;
            }
        }
        // Default to natural alignment, which is what LLVM does.
        // That is, use the size, rounded up to a power of 2.
        AbiAndPrefAlign::new(Align::from_bytes(vec_size.bytes().next_power_of_two()).unwrap())
    }
}

pub trait HasDataLayout {
    fn data_layout(&self) -> &TargetDataLayout;
}

impl HasDataLayout for TargetDataLayout {
    fn data_layout(&self) -> &TargetDataLayout {
        self
    }
}

/// Endianness of the target, which must match cfg(target-endian).
#[derive(Copy, Clone, PartialEq)]
pub enum Endian {
    Little,
    Big,
}

/// Size of a type in bytes.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Encodable, Decodable)]
#[derive(HashStable_Generic)]
pub struct Size {
    raw: u64,
}

impl Size {
    pub const ZERO: Size = Size { raw: 0 };

    #[inline]
    pub fn from_bits(bits: impl TryInto<u64>) -> Size {
        let bits = bits.try_into().ok().unwrap();
        // Avoid potential overflow from `bits + 7`.
        Size::from_bytes(bits / 8 + ((bits % 8) + 7) / 8)
    }

    #[inline]
    pub fn from_bytes(bytes: impl TryInto<u64>) -> Size {
        Size { raw: bytes.try_into().ok().unwrap() }
    }

    #[inline]
    pub fn bytes(self) -> u64 {
        self.raw
    }

    #[inline]
    pub fn bytes_usize(self) -> usize {
        self.bytes().try_into().unwrap()
    }

    #[inline]
    pub fn bits(self) -> u64 {
        self.bytes().checked_mul(8).unwrap_or_else(|| {
            panic!("Size::bits: {} bytes in bits doesn't fit in u64", self.bytes())
        })
    }

    #[inline]
    pub fn bits_usize(self) -> usize {
        self.bits().try_into().unwrap()
    }

    #[inline]
    pub fn align_to(self, align: Align) -> Size {
        let mask = align.bytes() - 1;
        Size::from_bytes((self.bytes() + mask) & !mask)
    }

    #[inline]
    pub fn is_aligned(self, align: Align) -> bool {
        let mask = align.bytes() - 1;
        self.bytes() & mask == 0
    }

    #[inline]
    pub fn checked_add<C: HasDataLayout>(self, offset: Size, cx: &C) -> Option<Size> {
        let dl = cx.data_layout();

        let bytes = self.bytes().checked_add(offset.bytes())?;

        if bytes < dl.obj_size_bound() { Some(Size::from_bytes(bytes)) } else { None }
    }

    #[inline]
    pub fn checked_mul<C: HasDataLayout>(self, count: u64, cx: &C) -> Option<Size> {
        let dl = cx.data_layout();

        let bytes = self.bytes().checked_mul(count)?;
        if bytes < dl.obj_size_bound() { Some(Size::from_bytes(bytes)) } else { None }
    }
}

// Panicking addition, subtraction and multiplication for convenience.
// Avoid during layout computation, return `LayoutError` instead.

impl Add for Size {
    type Output = Size;
    #[inline]
    fn add(self, other: Size) -> Size {
        Size::from_bytes(self.bytes().checked_add(other.bytes()).unwrap_or_else(|| {
            panic!("Size::add: {} + {} doesn't fit in u64", self.bytes(), other.bytes())
        }))
    }
}

impl Sub for Size {
    type Output = Size;
    #[inline]
    fn sub(self, other: Size) -> Size {
        Size::from_bytes(self.bytes().checked_sub(other.bytes()).unwrap_or_else(|| {
            panic!("Size::sub: {} - {} would result in negative size", self.bytes(), other.bytes())
        }))
    }
}

impl Mul<Size> for u64 {
    type Output = Size;
    #[inline]
    fn mul(self, size: Size) -> Size {
        size * self
    }
}

impl Mul<u64> for Size {
    type Output = Size;
    #[inline]
    fn mul(self, count: u64) -> Size {
        match self.bytes().checked_mul(count) {
            Some(bytes) => Size::from_bytes(bytes),
            None => panic!("Size::mul: {} * {} doesn't fit in u64", self.bytes(), count),
        }
    }
}

impl AddAssign for Size {
    #[inline]
    fn add_assign(&mut self, other: Size) {
        *self = *self + other;
    }
}

/// Alignment of a type in bytes (always a power of two).
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Encodable, Decodable)]
#[derive(HashStable_Generic)]
pub struct Align {
    pow2: u8,
}

impl Align {
    pub fn from_bits(bits: u64) -> Result<Align, String> {
        Align::from_bytes(Size::from_bits(bits).bytes())
    }

    pub fn from_bytes(align: u64) -> Result<Align, String> {
        // Treat an alignment of 0 bytes like 1-byte alignment.
        if align == 0 {
            return Ok(Align { pow2: 0 });
        }

        let mut bytes = align;
        let mut pow2: u8 = 0;
        while (bytes & 1) == 0 {
            pow2 += 1;
            bytes >>= 1;
        }
        if bytes != 1 {
            return Err(format!("`{}` is not a power of 2", align));
        }
        if pow2 > 29 {
            return Err(format!("`{}` is too large", align));
        }

        Ok(Align { pow2 })
    }

    pub fn bytes(self) -> u64 {
        1 << self.pow2
    }

    pub fn bits(self) -> u64 {
        self.bytes() * 8
    }

    /// Computes the best alignment possible for the given offset
    /// (the largest power of two that the offset is a multiple of).
    ///
    /// N.B., for an offset of `0`, this happens to return `2^64`.
    pub fn max_for_offset(offset: Size) -> Align {
        Align { pow2: offset.bytes().trailing_zeros() as u8 }
    }

    /// Lower the alignment, if necessary, such that the given offset
    /// is aligned to it (the offset is a multiple of the alignment).
    pub fn restrict_for_offset(self, offset: Size) -> Align {
        self.min(Align::max_for_offset(offset))
    }
}

/// A pair of alignments, ABI-mandated and preferred.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, Encodable, Decodable)]
#[derive(HashStable_Generic)]
pub struct AbiAndPrefAlign {
    pub abi: Align,
    pub pref: Align,
}

impl AbiAndPrefAlign {
    pub fn new(align: Align) -> AbiAndPrefAlign {
        AbiAndPrefAlign { abi: align, pref: align }
    }

    pub fn min(self, other: AbiAndPrefAlign) -> AbiAndPrefAlign {
        AbiAndPrefAlign { abi: self.abi.min(other.abi), pref: self.pref.min(other.pref) }
    }

    pub fn max(self, other: AbiAndPrefAlign) -> AbiAndPrefAlign {
        AbiAndPrefAlign { abi: self.abi.max(other.abi), pref: self.pref.max(other.pref) }
    }
}

/// Integers, also used for enum discriminants.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, HashStable_Generic)]
pub enum Integer {
    I8,
    I16,
    I32,
    I64,
    I128,
}

impl Integer {
    pub fn size(self) -> Size {
        match self {
            I8 => Size::from_bytes(1),
            I16 => Size::from_bytes(2),
            I32 => Size::from_bytes(4),
            I64 => Size::from_bytes(8),
            I128 => Size::from_bytes(16),
        }
    }

    pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign {
        let dl = cx.data_layout();

        match self {
            I8 => dl.i8_align,
            I16 => dl.i16_align,
            I32 => dl.i32_align,
            I64 => dl.i64_align,
            I128 => dl.i128_align,
        }
    }

    /// Finds the smallest Integer type which can represent the signed value.
    pub fn fit_signed(x: i128) -> Integer {
        match x {
            -0x0000_0000_0000_0080..=0x0000_0000_0000_007f => I8,
            -0x0000_0000_0000_8000..=0x0000_0000_0000_7fff => I16,
            -0x0000_0000_8000_0000..=0x0000_0000_7fff_ffff => I32,
            -0x8000_0000_0000_0000..=0x7fff_ffff_ffff_ffff => I64,
            _ => I128,
        }
    }

    /// Finds the smallest Integer type which can represent the unsigned value.
    pub fn fit_unsigned(x: u128) -> Integer {
        match x {
            0..=0x0000_0000_0000_00ff => I8,
            0..=0x0000_0000_0000_ffff => I16,
            0..=0x0000_0000_ffff_ffff => I32,
            0..=0xffff_ffff_ffff_ffff => I64,
            _ => I128,
        }
    }

    /// Finds the smallest integer with the given alignment.
    pub fn for_align<C: HasDataLayout>(cx: &C, wanted: Align) -> Option<Integer> {
        let dl = cx.data_layout();

        for &candidate in &[I8, I16, I32, I64, I128] {
            if wanted == candidate.align(dl).abi && wanted.bytes() == candidate.size().bytes() {
                return Some(candidate);
            }
        }
        None
    }

    /// Find the largest integer with the given alignment or less.
    pub fn approximate_align<C: HasDataLayout>(cx: &C, wanted: Align) -> Integer {
        let dl = cx.data_layout();

        // FIXME(eddyb) maybe include I128 in the future, when it works everywhere.
        for &candidate in &[I64, I32, I16] {
            if wanted >= candidate.align(dl).abi && wanted.bytes() >= candidate.size().bytes() {
                return candidate;
            }
        }
        I8
    }
}

/// Fundamental unit of memory access and layout.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
pub enum Primitive {
    /// The `bool` is the signedness of the `Integer` type.
    ///
    /// One would think we would not care about such details this low down,
    /// but some ABIs are described in terms of C types and ISAs where the
    /// integer arithmetic is done on {sign,zero}-extended registers, e.g.
    /// a negative integer passed by zero-extension will appear positive in
    /// the callee, and most operations on it will produce the wrong values.
    Int(Integer, bool),
    F32,
    F64,
    Pointer,
}

impl Primitive {
    pub fn size<C: HasDataLayout>(self, cx: &C) -> Size {
        let dl = cx.data_layout();

        match self {
            Int(i, _) => i.size(),
            F32 => Size::from_bits(32),
            F64 => Size::from_bits(64),
            Pointer => dl.pointer_size,
        }
    }

    pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign {
        let dl = cx.data_layout();

        match self {
            Int(i, _) => i.align(dl),
            F32 => dl.f32_align,
            F64 => dl.f64_align,
            Pointer => dl.pointer_align,
        }
    }

    pub fn is_float(self) -> bool {
        match self {
            F32 | F64 => true,
            _ => false,
        }
    }

    pub fn is_int(self) -> bool {
        match self {
            Int(..) => true,
            _ => false,
        }
    }
}

/// Information about one scalar component of a Rust type.
#[derive(Clone, PartialEq, Eq, Hash, Debug)]
#[derive(HashStable_Generic)]
pub struct Scalar {
    pub value: Primitive,

    /// Inclusive wrap-around range of valid values, that is, if
    /// start > end, it represents `start..=MAX`,
    /// followed by `0..=end`.
    ///
    /// That is, for an i8 primitive, a range of `254..=2` means following
    /// sequence:
    ///
    ///    254 (-2), 255 (-1), 0, 1, 2
    ///
    /// This is intended specifically to mirror LLVM’s `!range` metadata,
    /// semantics.
    // FIXME(eddyb) always use the shortest range, e.g., by finding
    // the largest space between two consecutive valid values and
    // taking everything else as the (shortest) valid range.
    pub valid_range: RangeInclusive<u128>,
}

impl Scalar {
    pub fn is_bool(&self) -> bool {
        if let Int(I8, _) = self.value { self.valid_range == (0..=1) } else { false }
    }

    /// Returns the valid range as a `x..y` range.
    ///
    /// If `x` and `y` are equal, the range is full, not empty.
    pub fn valid_range_exclusive<C: HasDataLayout>(&self, cx: &C) -> Range<u128> {
        // For a (max) value of -1, max will be `-1 as usize`, which overflows.
        // However, that is fine here (it would still represent the full range),
        // i.e., if the range is everything.
        let bits = self.value.size(cx).bits();
        assert!(bits <= 128);
        let mask = !0u128 >> (128 - bits);
        let start = *self.valid_range.start();
        let end = *self.valid_range.end();
        assert_eq!(start, start & mask);
        assert_eq!(end, end & mask);
        start..(end.wrapping_add(1) & mask)
    }
}

/// Describes how the fields of a type are located in memory.
#[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
pub enum FieldsShape {
    /// Scalar primitives and `!`, which never have fields.
    Primitive,

    /// All fields start at no offset. The `usize` is the field count.
    Union(NonZeroUsize),

    /// Array/vector-like placement, with all fields of identical types.
    Array { stride: Size, count: u64 },

    /// Struct-like placement, with precomputed offsets.
    ///
    /// Fields are guaranteed to not overlap, but note that gaps
    /// before, between and after all the fields are NOT always
    /// padding, and as such their contents may not be discarded.
    /// For example, enum variants leave a gap at the start,
    /// where the discriminant field in the enum layout goes.
    Arbitrary {
        /// Offsets for the first byte of each field,
        /// ordered to match the source definition order.
        /// This vector does not go in increasing order.
        // FIXME(eddyb) use small vector optimization for the common case.
        offsets: Vec<Size>,

        /// Maps source order field indices to memory order indices,
        /// depending on how the fields were reordered (if at all).
        /// This is a permutation, with both the source order and the
        /// memory order using the same (0..n) index ranges.
        ///
        /// Note that during computation of `memory_index`, sometimes
        /// it is easier to operate on the inverse mapping (that is,
        /// from memory order to source order), and that is usually
        /// named `inverse_memory_index`.
        ///
        // FIXME(eddyb) build a better abstraction for permutations, if possible.
        // FIXME(camlorn) also consider small vector  optimization here.
        memory_index: Vec<u32>,
    },
}

impl FieldsShape {
    pub fn count(&self) -> usize {
        match *self {
            FieldsShape::Primitive => 0,
            FieldsShape::Union(count) => count.get(),
            FieldsShape::Array { count, .. } => {
                let usize_count = count as usize;
                assert_eq!(usize_count as u64, count);
                usize_count
            }
            FieldsShape::Arbitrary { ref offsets, .. } => offsets.len(),
        }
    }

    pub fn offset(&self, i: usize) -> Size {
        match *self {
            FieldsShape::Primitive => {
                unreachable!("FieldsShape::offset: `Primitive`s have no fields")
            }
            FieldsShape::Union(count) => {
                assert!(
                    i < count.get(),
                    "tried to access field {} of union with {} fields",
                    i,
                    count
                );
                Size::ZERO
            }
            FieldsShape::Array { stride, count } => {
                let i = u64::try_from(i).unwrap();
                assert!(i < count);
                stride * i
            }
            FieldsShape::Arbitrary { ref offsets, .. } => offsets[i],
        }
    }

    pub fn memory_index(&self, i: usize) -> usize {
        match *self {
            FieldsShape::Primitive => {
                unreachable!("FieldsShape::memory_index: `Primitive`s have no fields")
            }
            FieldsShape::Union(_) | FieldsShape::Array { .. } => i,
            FieldsShape::Arbitrary { ref memory_index, .. } => {
                let r = memory_index[i];
                assert_eq!(r as usize as u32, r);
                r as usize
            }
        }
    }

    /// Gets source indices of the fields by increasing offsets.
    #[inline]
    pub fn index_by_increasing_offset<'a>(&'a self) -> impl Iterator<Item = usize> + 'a {
        let mut inverse_small = [0u8; 64];
        let mut inverse_big = vec![];
        let use_small = self.count() <= inverse_small.len();

        // We have to write this logic twice in order to keep the array small.
        if let FieldsShape::Arbitrary { ref memory_index, .. } = *self {
            if use_small {
                for i in 0..self.count() {
                    inverse_small[memory_index[i] as usize] = i as u8;
                }
            } else {
                inverse_big = vec![0; self.count()];
                for i in 0..self.count() {
                    inverse_big[memory_index[i] as usize] = i as u32;
                }
            }
        }

        (0..self.count()).map(move |i| match *self {
            FieldsShape::Primitive | FieldsShape::Union(_) | FieldsShape::Array { .. } => i,
            FieldsShape::Arbitrary { .. } => {
                if use_small {
                    inverse_small[i] as usize
                } else {
                    inverse_big[i] as usize
                }
            }
        })
    }
}

/// An identifier that specifies the address space that some operation
/// should operate on. Special address spaces have an effect on code generation,
/// depending on the target and the address spaces it implements.
#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
pub struct AddressSpace(pub u32);

impl AddressSpace {
    /// The default address space, corresponding to data space.
    pub const DATA: Self = AddressSpace(0);
}

/// Describes how values of the type are passed by target ABIs,
/// in terms of categories of C types there are ABI rules for.
#[derive(Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
pub enum Abi {
    Uninhabited,
    Scalar(Scalar),
    ScalarPair(Scalar, Scalar),
    Vector {
        element: Scalar,
        count: u64,
    },
    Aggregate {
        /// If true, the size is exact, otherwise it's only a lower bound.
        sized: bool,
    },
}

impl Abi {
    /// Returns `true` if the layout corresponds to an unsized type.
    pub fn is_unsized(&self) -> bool {
        match *self {
            Abi::Uninhabited | Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } => false,
            Abi::Aggregate { sized } => !sized,
        }
    }

    /// Returns `true` if this is a single signed integer scalar
    pub fn is_signed(&self) -> bool {
        match *self {
            Abi::Scalar(ref scal) => match scal.value {
                Primitive::Int(_, signed) => signed,
                _ => false,
            },
            _ => panic!("`is_signed` on non-scalar ABI {:?}", self),
        }
    }

    /// Returns `true` if this is an uninhabited type
    pub fn is_uninhabited(&self) -> bool {
        match *self {
            Abi::Uninhabited => true,
            _ => false,
        }
    }

    /// Returns `true` is this is a scalar type
    pub fn is_scalar(&self) -> bool {
        match *self {
            Abi::Scalar(_) => true,
            _ => false,
        }
    }
}

rustc_index::newtype_index! {
    pub struct VariantIdx {
        derive [HashStable_Generic]
    }
}

#[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
pub enum Variants {
    /// Single enum variants, structs/tuples, unions, and all non-ADTs.
    Single { index: VariantIdx },

    /// Enum-likes with more than one inhabited variant: each variant comes with
    /// a *discriminant* (usually the same as the variant index but the user can
    /// assign explicit discriminant values).  That discriminant is encoded
    /// as a *tag* on the machine.  The layout of each variant is
    /// a struct, and they all have space reserved for the tag.
    /// For enums, the tag is the sole field of the layout.
    Multiple {
        tag: Scalar,
        tag_encoding: TagEncoding,
        tag_field: usize,
        variants: IndexVec<VariantIdx, Layout>,
    },
}

#[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
pub enum TagEncoding {
    /// The tag directly stores the discriminant, but possibly with a smaller layout
    /// (so converting the tag to the discriminant can require sign extension).
    Direct,

    /// Niche (values invalid for a type) encoding the discriminant:
    /// Discriminant and variant index coincide.
    /// The variant `dataful_variant` contains a niche at an arbitrary
    /// offset (field `tag_field` of the enum), which for a variant with
    /// discriminant `d` is set to
    /// `(d - niche_variants.start).wrapping_add(niche_start)`.
    ///
    /// For example, `Option<(usize, &T)>`  is represented such that
    /// `None` has a null pointer for the second tuple field, and
    /// `Some` is the identity function (with a non-null reference).
    Niche {
        dataful_variant: VariantIdx,
        niche_variants: RangeInclusive<VariantIdx>,
        niche_start: u128,
    },
}

#[derive(Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
pub struct Niche {
    pub offset: Size,
    pub scalar: Scalar,
}

impl Niche {
    pub fn from_scalar<C: HasDataLayout>(cx: &C, offset: Size, scalar: Scalar) -> Option<Self> {
        let niche = Niche { offset, scalar };
        if niche.available(cx) > 0 { Some(niche) } else { None }
    }

    pub fn available<C: HasDataLayout>(&self, cx: &C) -> u128 {
        let Scalar { value, valid_range: ref v } = self.scalar;
        let bits = value.size(cx).bits();
        assert!(bits <= 128);
        let max_value = !0u128 >> (128 - bits);

        // Find out how many values are outside the valid range.
        let niche = v.end().wrapping_add(1)..*v.start();
        niche.end.wrapping_sub(niche.start) & max_value
    }

    pub fn reserve<C: HasDataLayout>(&self, cx: &C, count: u128) -> Option<(u128, Scalar)> {
        assert!(count > 0);

        let Scalar { value, valid_range: ref v } = self.scalar;
        let bits = value.size(cx).bits();
        assert!(bits <= 128);
        let max_value = !0u128 >> (128 - bits);

        if count > max_value {
            return None;
        }

        // Compute the range of invalid values being reserved.
        let start = v.end().wrapping_add(1) & max_value;
        let end = v.end().wrapping_add(count) & max_value;

        // If the `end` of our range is inside the valid range,
        // then we ran out of invalid values.
        // FIXME(eddyb) abstract this with a wraparound range type.
        let valid_range_contains = |x| {
            if v.start() <= v.end() {
                *v.start() <= x && x <= *v.end()
            } else {
                *v.start() <= x || x <= *v.end()
            }
        };
        if valid_range_contains(end) {
            return None;
        }

        Some((start, Scalar { value, valid_range: *v.start()..=end }))
    }
}

#[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
pub struct Layout {
    /// Says where the fields are located within the layout.
    pub fields: FieldsShape,

    /// Encodes information about multi-variant layouts.
    /// Even with `Multiple` variants, a layout still has its own fields! Those are then
    /// shared between all variants. One of them will be the discriminant,
    /// but e.g. generators can have more.
    ///
    /// To access all fields of this layout, both `fields` and the fields of the active variant
    /// must be taken into account.
    pub variants: Variants,

    /// The `abi` defines how this data is passed between functions, and it defines
    /// value restrictions via `valid_range`.
    ///
    /// Note that this is entirely orthogonal to the recursive structure defined by
    /// `variants` and `fields`; for example, `ManuallyDrop<Result<isize, isize>>` has
    /// `Abi::ScalarPair`! So, even with non-`Aggregate` `abi`, `fields` and `variants`
    /// have to be taken into account to find all fields of this layout.
    pub abi: Abi,

    /// The leaf scalar with the largest number of invalid values
    /// (i.e. outside of its `valid_range`), if it exists.
    pub largest_niche: Option<Niche>,

    pub align: AbiAndPrefAlign,
    pub size: Size,
}

impl Layout {
    pub fn scalar<C: HasDataLayout>(cx: &C, scalar: Scalar) -> Self {
        let largest_niche = Niche::from_scalar(cx, Size::ZERO, scalar.clone());
        let size = scalar.value.size(cx);
        let align = scalar.value.align(cx);
        Layout {
            variants: Variants::Single { index: VariantIdx::new(0) },
            fields: FieldsShape::Primitive,
            abi: Abi::Scalar(scalar),
            largest_niche,
            size,
            align,
        }
    }
}

/// The layout of a type, alongside the type itself.
/// Provides various type traversal APIs (e.g., recursing into fields).
///
/// Note that the layout is NOT guaranteed to always be identical
/// to that obtained from `layout_of(ty)`, as we need to produce
/// layouts for which Rust types do not exist, such as enum variants
/// or synthetic fields of enums (i.e., discriminants) and fat pointers.
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
pub struct TyAndLayout<'a, Ty> {
    pub ty: Ty,
    pub layout: &'a Layout,
}

impl<'a, Ty> Deref for TyAndLayout<'a, Ty> {
    type Target = &'a Layout;
    fn deref(&self) -> &&'a Layout {
        &self.layout
    }
}

/// Trait for context types that can compute layouts of things.
pub trait LayoutOf {
    type Ty;
    type TyAndLayout;

    fn layout_of(&self, ty: Self::Ty) -> Self::TyAndLayout;
    fn spanned_layout_of(&self, ty: Self::Ty, _span: Span) -> Self::TyAndLayout {
        self.layout_of(ty)
    }
}

/// The `TyAndLayout` above will always be a `MaybeResult<TyAndLayout<'_, Self>>`.
/// We can't add the bound due to the lifetime, but this trait is still useful when
/// writing code that's generic over the `LayoutOf` impl.
pub trait MaybeResult<T> {
    type Error;

    fn from(x: Result<T, Self::Error>) -> Self;
    fn to_result(self) -> Result<T, Self::Error>;
}

impl<T> MaybeResult<T> for T {
    type Error = !;

    fn from(Ok(x): Result<T, Self::Error>) -> Self {
        x
    }
    fn to_result(self) -> Result<T, Self::Error> {
        Ok(self)
    }
}

impl<T, E> MaybeResult<T> for Result<T, E> {
    type Error = E;

    fn from(x: Result<T, Self::Error>) -> Self {
        x
    }
    fn to_result(self) -> Result<T, Self::Error> {
        self
    }
}

#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum PointerKind {
    /// Most general case, we know no restrictions to tell LLVM.
    Shared,

    /// `&T` where `T` contains no `UnsafeCell`, is `noalias` and `readonly`.
    Frozen,

    /// `&mut T`, when we know `noalias` is safe for LLVM.
    UniqueBorrowed,

    /// `Box<T>`, unlike `UniqueBorrowed`, it also has `noalias` on returns.
    UniqueOwned,
}

#[derive(Copy, Clone, Debug)]
pub struct PointeeInfo {
    pub size: Size,
    pub align: Align,
    pub safe: Option<PointerKind>,
    pub address_space: AddressSpace,
}

pub trait TyAndLayoutMethods<'a, C: LayoutOf<Ty = Self>>: Sized {
    fn for_variant(
        this: TyAndLayout<'a, Self>,
        cx: &C,
        variant_index: VariantIdx,
    ) -> TyAndLayout<'a, Self>;
    fn field(this: TyAndLayout<'a, Self>, cx: &C, i: usize) -> C::TyAndLayout;
    fn pointee_info_at(this: TyAndLayout<'a, Self>, cx: &C, offset: Size) -> Option<PointeeInfo>;
}

impl<'a, Ty> TyAndLayout<'a, Ty> {
    pub fn for_variant<C>(self, cx: &C, variant_index: VariantIdx) -> Self
    where
        Ty: TyAndLayoutMethods<'a, C>,
        C: LayoutOf<Ty = Ty>,
    {
        Ty::for_variant(self, cx, variant_index)
    }

    /// Callers might want to use `C: LayoutOf<Ty=Ty, TyAndLayout: MaybeResult<Self>>`
    /// to allow recursion (see `might_permit_zero_init` below for an example).
    pub fn field<C>(self, cx: &C, i: usize) -> C::TyAndLayout
    where
        Ty: TyAndLayoutMethods<'a, C>,
        C: LayoutOf<Ty = Ty>,
    {
        Ty::field(self, cx, i)
    }

    pub fn pointee_info_at<C>(self, cx: &C, offset: Size) -> Option<PointeeInfo>
    where
        Ty: TyAndLayoutMethods<'a, C>,
        C: LayoutOf<Ty = Ty>,
    {
        Ty::pointee_info_at(self, cx, offset)
    }
}

impl<'a, Ty> TyAndLayout<'a, Ty> {
    /// Returns `true` if the layout corresponds to an unsized type.
    pub fn is_unsized(&self) -> bool {
        self.abi.is_unsized()
    }

    /// Returns `true` if the type is a ZST and not unsized.
    pub fn is_zst(&self) -> bool {
        match self.abi {
            Abi::Scalar(_) | Abi::ScalarPair(..) | Abi::Vector { .. } => false,
            Abi::Uninhabited => self.size.bytes() == 0,
            Abi::Aggregate { sized } => sized && self.size.bytes() == 0,
        }
    }

    /// Determines if this type permits "raw" initialization by just transmuting some
    /// memory into an instance of `T`.
    /// `zero` indicates if the memory is zero-initialized, or alternatively
    /// left entirely uninitialized.
    /// This is conservative: in doubt, it will answer `true`.
    ///
    /// FIXME: Once we removed all the conservatism, we could alternatively
    /// create an all-0/all-undef constant and run the const value validator to see if
    /// this is a valid value for the given type.
    pub fn might_permit_raw_init<C, E>(self, cx: &C, zero: bool) -> Result<bool, E>
    where
        Self: Copy,
        Ty: TyAndLayoutMethods<'a, C>,
        C: LayoutOf<Ty = Ty, TyAndLayout: MaybeResult<Self, Error = E>> + HasDataLayout,
    {
        let scalar_allows_raw_init = move |s: &Scalar| -> bool {
            if zero {
                let range = &s.valid_range;
                // The range must contain 0.
                range.contains(&0) || (*range.start() > *range.end()) // wrap-around allows 0
            } else {
                // The range must include all values. `valid_range_exclusive` handles
                // the wrap-around using target arithmetic; with wrap-around then the full
                // range is one where `start == end`.
                let range = s.valid_range_exclusive(cx);
                range.start == range.end
            }
        };

        // Check the ABI.
        let valid = match &self.abi {
            Abi::Uninhabited => false, // definitely UB
            Abi::Scalar(s) => scalar_allows_raw_init(s),
            Abi::ScalarPair(s1, s2) => scalar_allows_raw_init(s1) && scalar_allows_raw_init(s2),
            Abi::Vector { element: s, count } => *count == 0 || scalar_allows_raw_init(s),
            Abi::Aggregate { .. } => true, // Cannot be excluded *right now*.
        };
        if !valid {
            // This is definitely not okay.
            trace!("might_permit_raw_init({:?}, zero={}): not valid", self.layout, zero);
            return Ok(false);
        }

        // If we have not found an error yet, we need to recursively descend.
        // FIXME(#66151): For now, we are conservative and do not do this.
        Ok(true)
    }
}