src/librustc_target/abi/mod.rs

   1 pub use Integer::*;
   2 pub use Primitive::*;
   3
   4 use crate::spec::Target;
   5
   6 use std::ops::{Add, Deref, Sub, Mul, AddAssign, Range, RangeInclusive};
   7
   8 use rustc_index::vec::{Idx, IndexVec};
   9 use rustc_macros::HashStable_Generic;
  10 use syntax_pos::Span;
  11
  12 pub mod call;
  13
  14 /// Parsed [Data layout](http://llvm.org/docs/LangRef.html#data-layout)
  15 /// for a target, which contains everything needed to compute layouts.
  16 pub struct TargetDataLayout {
  17     pub endian: Endian,
  18     pub i1_align: AbiAndPrefAlign,
  19     pub i8_align: AbiAndPrefAlign,
  20     pub i16_align: AbiAndPrefAlign,
  21     pub i32_align: AbiAndPrefAlign,
  22     pub i64_align: AbiAndPrefAlign,
  23     pub i128_align: AbiAndPrefAlign,
  24     pub f32_align: AbiAndPrefAlign,
  25     pub f64_align: AbiAndPrefAlign,
  26     pub pointer_size: Size,
  27     pub pointer_align: AbiAndPrefAlign,
  28     pub aggregate_align: AbiAndPrefAlign,
  29
  30     /// Alignments for vector types.
  31     pub vector_align: Vec<(Size, AbiAndPrefAlign)>,
  32
  33     pub instruction_address_space: u32,
  34 }
  35
  36 impl Default for TargetDataLayout {
  37     /// Creates an instance of `TargetDataLayout`.
  38     fn default() -> TargetDataLayout {
  39         let align = |bits| Align::from_bits(bits).unwrap();
  40         TargetDataLayout {
  41             endian: Endian::Big,
  42             i1_align: AbiAndPrefAlign::new(align(8)),
  43             i8_align: AbiAndPrefAlign::new(align(8)),
  44             i16_align: AbiAndPrefAlign::new(align(16)),
  45             i32_align: AbiAndPrefAlign::new(align(32)),
  46             i64_align: AbiAndPrefAlign { abi: align(32), pref: align(64) },
  47             i128_align: AbiAndPrefAlign { abi: align(32), pref: align(64) },
  48             f32_align: AbiAndPrefAlign::new(align(32)),
  49             f64_align: AbiAndPrefAlign::new(align(64)),
  50             pointer_size: Size::from_bits(64),
  51             pointer_align: AbiAndPrefAlign::new(align(64)),
  52             aggregate_align: AbiAndPrefAlign { abi: align(0), pref: align(64) },
  53             vector_align: vec![
  54                 (Size::from_bits(64), AbiAndPrefAlign::new(align(64))),
  55                 (Size::from_bits(128), AbiAndPrefAlign::new(align(128))),
  56             ],
  57             instruction_address_space: 0,
  58         }
  59     }
  60 }
  61
  62 impl TargetDataLayout {
  63     pub fn parse(target: &Target) -> Result<TargetDataLayout, String> {
  64         // Parse an address space index from a string.
  65         let parse_address_space = |s: &str, cause: &str| {
  66             s.parse::<u32>().map_err(|err| {
  67                 format!("invalid address space `{}` for `{}` in \"data-layout\": {}",
  68                         s, cause, err)
  69             })
  70         };
  71
  72         // Parse a bit count from a string.
  73         let parse_bits = |s: &str, kind: &str, cause: &str| {
  74             s.parse::<u64>().map_err(|err| {
  75                 format!("invalid {} `{}` for `{}` in \"data-layout\": {}",
  76                         kind, s, cause, err)
  77             })
  78         };
  79
  80         // Parse a size string.
  81         let size = |s: &str, cause: &str| {
  82             parse_bits(s, "size", cause).map(Size::from_bits)
  83         };
  84
  85         // Parse an alignment string.
  86         let align = |s: &[&str], cause: &str| {
  87             if s.is_empty() {
  88                 return Err(format!("missing alignment for `{}` in \"data-layout\"", cause));
  89             }
  90             let align_from_bits = |bits| {
  91                 Align::from_bits(bits).map_err(|err| {
  92                     format!("invalid alignment for `{}` in \"data-layout\": {}",
  93                             cause, err)
  94                 })
  95             };
  96             let abi = parse_bits(s[0], "alignment", cause)?;
  97             let pref = s.get(1).map_or(Ok(abi), |pref| parse_bits(pref, "alignment", cause))?;
  98             Ok(AbiAndPrefAlign {
  99                 abi: align_from_bits(abi)?,
 100                 pref: align_from_bits(pref)?,
 101             })
 102         };
 103
 104         let mut dl = TargetDataLayout::default();
 105         let mut i128_align_src = 64;
 106         for spec in target.data_layout.split('-') {
 107             let spec_parts = spec.split(':').collect::<Vec<_>>();
 108
 109             match &*spec_parts {
 110                 ["e"] => dl.endian = Endian::Little,
 111                 ["E"] => dl.endian = Endian::Big,
 112                 [p] if p.starts_with("P") => {
 113                     dl.instruction_address_space = parse_address_space(&p[1..], "P")?
 114                 }
 115                 ["a", ref a @ ..] => {
 116                     dl.aggregate_align = align(a, "a")?
 117                 }
 118                 ["f32", ref a @ ..] => {
 119                     dl.f32_align = align(a, "f32")?
 120                 }
 121                 ["f64", ref a @ ..] => {
 122                     dl.f64_align = align(a, "f64")?
 123                 }
 124                 [p @ "p", s, ref a @ ..] | [p @ "p0", s, ref a @ ..] => {
 125                     dl.pointer_size = size(s, p)?;
 126                     dl.pointer_align = align(a, p)?;
 127                 }
 128                 [s, ref a @ ..] if s.starts_with("i") => {
 129                     let bits = match s[1..].parse::<u64>() {
 130                         Ok(bits) => bits,
 131                         Err(_) => {
 132                             size(&s[1..], "i")?; // For the user error.
 133                             continue;
 134                         }
 135                     };
 136                     let a = align(a, s)?;
 137                     match bits {
 138                         1 => dl.i1_align = a,
 139                         8 => dl.i8_align = a,
 140                         16 => dl.i16_align = a,
 141                         32 => dl.i32_align = a,
 142                         64 => dl.i64_align = a,
 143                         _ => {}
 144                     }
 145                     if bits >= i128_align_src && bits <= 128 {
 146                         // Default alignment for i128 is decided by taking the alignment of
 147                         // largest-sized i{64..=128}.
 148                         i128_align_src = bits;
 149                         dl.i128_align = a;
 150                     }
 151                 }
 152                 [s, ref a @ ..] if s.starts_with("v") => {
 153                     let v_size = size(&s[1..], "v")?;
 154                     let a = align(a, s)?;
 155                     if let Some(v) = dl.vector_align.iter_mut().find(|v| v.0 == v_size) {
 156                         v.1 = a;
 157                         continue;
 158                     }
 159                     // No existing entry, add a new one.
 160                     dl.vector_align.push((v_size, a));
 161                 }
 162                 _ => {} // Ignore everything else.
 163             }
 164         }
 165
 166         // Perform consistency checks against the Target information.
 167         let endian_str = match dl.endian {
 168             Endian::Little => "little",
 169             Endian::Big => "big"
 170         };
 171         if endian_str != target.target_endian {
 172             return Err(format!("inconsistent target specification: \"data-layout\" claims \
 173                                 architecture is {}-endian, while \"target-endian\" is `{}`",
 174                                endian_str, target.target_endian));
 175         }
 176
 177         if dl.pointer_size.bits().to_string() != target.target_pointer_width {
 178             return Err(format!("inconsistent target specification: \"data-layout\" claims \
 179                                 pointers are {}-bit, while \"target-pointer-width\" is `{}`",
 180                                dl.pointer_size.bits(), target.target_pointer_width));
 181         }
 182
 183         Ok(dl)
 184     }
 185
 186     /// Returns exclusive upper bound on object size.
 187     ///
 188     /// The theoretical maximum object size is defined as the maximum positive `isize` value.
 189     /// This ensures that the `offset` semantics remain well-defined by allowing it to correctly
 190     /// index every address within an object along with one byte past the end, along with allowing
 191     /// `isize` to store the difference between any two pointers into an object.
 192     ///
 193     /// The upper bound on 64-bit currently needs to be lower because LLVM uses a 64-bit integer
 194     /// to represent object size in bits. It would need to be 1 << 61 to account for this, but is
 195     /// currently conservatively bounded to 1 << 47 as that is enough to cover the current usable
 196     /// address space on 64-bit ARMv8 and x86_64.
 197     pub fn obj_size_bound(&self) -> u64 {
 198         match self.pointer_size.bits() {
 199             16 => 1 << 15,
 200             32 => 1 << 31,
 201             64 => 1 << 47,
 202             bits => panic!("obj_size_bound: unknown pointer bit size {}", bits)
 203         }
 204     }
 205
 206     pub fn ptr_sized_integer(&self) -> Integer {
 207         match self.pointer_size.bits() {
 208             16 => I16,
 209             32 => I32,
 210             64 => I64,
 211             bits => panic!("ptr_sized_integer: unknown pointer bit size {}", bits)
 212         }
 213     }
 214
 215     pub fn vector_align(&self, vec_size: Size) -> AbiAndPrefAlign {
 216         for &(size, align) in &self.vector_align {
 217             if size == vec_size {
 218                 return align;
 219             }
 220         }
 221         // Default to natural alignment, which is what LLVM does.
 222         // That is, use the size, rounded up to a power of 2.
 223         AbiAndPrefAlign::new(Align::from_bytes(vec_size.bytes().next_power_of_two()).unwrap())
 224     }
 225 }
 226
 227 pub trait HasDataLayout {
 228     fn data_layout(&self) -> &TargetDataLayout;
 229 }
 230
 231 impl HasDataLayout for TargetDataLayout {
 232     fn data_layout(&self) -> &TargetDataLayout {
 233         self
 234     }
 235 }
 236
 237 /// Endianness of the target, which must match cfg(target-endian).
 238 #[derive(Copy, Clone, PartialEq)]
 239 pub enum Endian {
 240     Little,
 241     Big
 242 }
 243
 244 /// Size of a type in bytes.
 245 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
 246 #[derive(HashStable_Generic)]
 247 pub struct Size {
 248     raw: u64
 249 }
 250
 251 impl Size {
 252     pub const ZERO: Size = Self::from_bytes(0);
 253
 254     #[inline]
 255     pub fn from_bits(bits: u64) -> Size {
 256         // Avoid potential overflow from `bits + 7`.
 257         Size::from_bytes(bits / 8 + ((bits % 8) + 7) / 8)
 258     }
 259
 260     #[inline]
 261     pub const fn from_bytes(bytes: u64) -> Size {
 262         Size {
 263             raw: bytes
 264         }
 265     }
 266
 267     #[inline]
 268     pub fn bytes(self) -> u64 {
 269         self.raw
 270     }
 271
 272     #[inline]
 273     pub fn bits(self) -> u64 {
 274         self.bytes().checked_mul(8).unwrap_or_else(|| {
 275             panic!("Size::bits: {} bytes in bits doesn't fit in u64", self.bytes())
 276         })
 277     }
 278
 279     #[inline]
 280     pub fn align_to(self, align: Align) -> Size {
 281         let mask = align.bytes() - 1;
 282         Size::from_bytes((self.bytes() + mask) & !mask)
 283     }
 284
 285     #[inline]
 286     pub fn is_aligned(self, align: Align) -> bool {
 287         let mask = align.bytes() - 1;
 288         self.bytes() & mask == 0
 289     }
 290
 291     #[inline]
 292     pub fn checked_add<C: HasDataLayout>(self, offset: Size, cx: &C) -> Option<Size> {
 293         let dl = cx.data_layout();
 294
 295         let bytes = self.bytes().checked_add(offset.bytes())?;
 296
 297         if bytes < dl.obj_size_bound() {
 298             Some(Size::from_bytes(bytes))
 299         } else {
 300             None
 301         }
 302     }
 303
 304     #[inline]
 305     pub fn checked_mul<C: HasDataLayout>(self, count: u64, cx: &C) -> Option<Size> {
 306         let dl = cx.data_layout();
 307
 308         let bytes = self.bytes().checked_mul(count)?;
 309         if bytes < dl.obj_size_bound() {
 310             Some(Size::from_bytes(bytes))
 311         } else {
 312             None
 313         }
 314     }
 315 }
 316
 317 // Panicking addition, subtraction and multiplication for convenience.
 318 // Avoid during layout computation, return `LayoutError` instead.
 319
 320 impl Add for Size {
 321     type Output = Size;
 322     #[inline]
 323     fn add(self, other: Size) -> Size {
 324         Size::from_bytes(self.bytes().checked_add(other.bytes()).unwrap_or_else(|| {
 325             panic!("Size::add: {} + {} doesn't fit in u64", self.bytes(), other.bytes())
 326         }))
 327     }
 328 }
 329
 330 impl Sub for Size {
 331     type Output = Size;
 332     #[inline]
 333     fn sub(self, other: Size) -> Size {
 334         Size::from_bytes(self.bytes().checked_sub(other.bytes()).unwrap_or_else(|| {
 335             panic!("Size::sub: {} - {} would result in negative size", self.bytes(), other.bytes())
 336         }))
 337     }
 338 }
 339
 340 impl Mul<Size> for u64 {
 341     type Output = Size;
 342     #[inline]
 343     fn mul(self, size: Size) -> Size {
 344         size * self
 345     }
 346 }
 347
 348 impl Mul<u64> for Size {
 349     type Output = Size;
 350     #[inline]
 351     fn mul(self, count: u64) -> Size {
 352         match self.bytes().checked_mul(count) {
 353             Some(bytes) => Size::from_bytes(bytes),
 354             None => {
 355                 panic!("Size::mul: {} * {} doesn't fit in u64", self.bytes(), count)
 356             }
 357         }
 358     }
 359 }
 360
 361 impl AddAssign for Size {
 362     #[inline]
 363     fn add_assign(&mut self, other: Size) {
 364         *self = *self + other;
 365     }
 366 }
 367
 368 /// Alignment of a type in bytes (always a power of two).
 369 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, RustcEncodable, RustcDecodable)]
 370 #[derive(HashStable_Generic)]
 371 pub struct Align {
 372     pow2: u8,
 373 }
 374
 375 impl Align {
 376     pub fn from_bits(bits: u64) -> Result<Align, String> {
 377         Align::from_bytes(Size::from_bits(bits).bytes())
 378     }
 379
 380     pub fn from_bytes(align: u64) -> Result<Align, String> {
 381         // Treat an alignment of 0 bytes like 1-byte alignment.
 382         if align == 0 {
 383             return Ok(Align { pow2: 0 });
 384         }
 385
 386         let mut bytes = align;
 387         let mut pow2: u8 = 0;
 388         while (bytes & 1) == 0 {
 389             pow2 += 1;
 390             bytes >>= 1;
 391         }
 392         if bytes != 1 {
 393             return Err(format!("`{}` is not a power of 2", align));
 394         }
 395         if pow2 > 29 {
 396             return Err(format!("`{}` is too large", align));
 397         }
 398
 399         Ok(Align { pow2 })
 400     }
 401
 402     pub fn bytes(self) -> u64 {
 403         1 << self.pow2
 404     }
 405
 406     pub fn bits(self) -> u64 {
 407         self.bytes() * 8
 408     }
 409
 410     /// Computes the best alignment possible for the given offset
 411     /// (the largest power of two that the offset is a multiple of).
 412     ///
 413     /// N.B., for an offset of `0`, this happens to return `2^64`.
 414     pub fn max_for_offset(offset: Size) -> Align {
 415         Align {
 416             pow2: offset.bytes().trailing_zeros() as u8,
 417         }
 418     }
 419
 420     /// Lower the alignment, if necessary, such that the given offset
 421     /// is aligned to it (the offset is a multiple of the alignment).
 422     pub fn restrict_for_offset(self, offset: Size) -> Align {
 423         self.min(Align::max_for_offset(offset))
 424     }
 425 }
 426
 427 /// A pair of aligments, ABI-mandated and preferred.
 428 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
 429 #[derive(HashStable_Generic)]
 430 pub struct AbiAndPrefAlign {
 431     pub abi: Align,
 432     pub pref: Align,
 433 }
 434
 435 impl AbiAndPrefAlign {
 436     pub fn new(align: Align) -> AbiAndPrefAlign {
 437         AbiAndPrefAlign {
 438             abi: align,
 439             pref: align,
 440         }
 441     }
 442
 443     pub fn min(self, other: AbiAndPrefAlign) -> AbiAndPrefAlign {
 444         AbiAndPrefAlign {
 445             abi: self.abi.min(other.abi),
 446             pref: self.pref.min(other.pref),
 447         }
 448     }
 449
 450     pub fn max(self, other: AbiAndPrefAlign) -> AbiAndPrefAlign {
 451         AbiAndPrefAlign {
 452             abi: self.abi.max(other.abi),
 453             pref: self.pref.max(other.pref),
 454         }
 455     }
 456 }
 457
 458 /// Integers, also used for enum discriminants.
 459 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, HashStable_Generic)]
 460 pub enum Integer {
 461     I8,
 462     I16,
 463     I32,
 464     I64,
 465     I128,
 466 }
 467
 468 impl Integer {
 469     pub fn size(self) -> Size {
 470         match self {
 471             I8 => Size::from_bytes(1),
 472             I16 => Size::from_bytes(2),
 473             I32 => Size::from_bytes(4),
 474             I64  => Size::from_bytes(8),
 475             I128  => Size::from_bytes(16),
 476         }
 477     }
 478
 479     pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign {
 480         let dl = cx.data_layout();
 481
 482         match self {
 483             I8 => dl.i8_align,
 484             I16 => dl.i16_align,
 485             I32 => dl.i32_align,
 486             I64 => dl.i64_align,
 487             I128 => dl.i128_align,
 488         }
 489     }
 490
 491     /// Finds the smallest Integer type which can represent the signed value.
 492     pub fn fit_signed(x: i128) -> Integer {
 493         match x {
 494             -0x0000_0000_0000_0080..=0x0000_0000_0000_007f => I8,
 495             -0x0000_0000_0000_8000..=0x0000_0000_0000_7fff => I16,
 496             -0x0000_0000_8000_0000..=0x0000_0000_7fff_ffff => I32,
 497             -0x8000_0000_0000_0000..=0x7fff_ffff_ffff_ffff => I64,
 498             _ => I128
 499         }
 500     }
 501
 502     /// Finds the smallest Integer type which can represent the unsigned value.
 503     pub fn fit_unsigned(x: u128) -> Integer {
 504         match x {
 505             0..=0x0000_0000_0000_00ff => I8,
 506             0..=0x0000_0000_0000_ffff => I16,
 507             0..=0x0000_0000_ffff_ffff => I32,
 508             0..=0xffff_ffff_ffff_ffff => I64,
 509             _ => I128,
 510         }
 511     }
 512
 513     /// Finds the smallest integer with the given alignment.
 514     pub fn for_align<C: HasDataLayout>(cx: &C, wanted: Align) -> Option<Integer> {
 515         let dl = cx.data_layout();
 516
 517         for &candidate in &[I8, I16, I32, I64, I128] {
 518             if wanted == candidate.align(dl).abi && wanted.bytes() == candidate.size().bytes() {
 519                 return Some(candidate);
 520             }
 521         }
 522         None
 523     }
 524
 525     /// Find the largest integer with the given alignment or less.
 526     pub fn approximate_align<C: HasDataLayout>(cx: &C, wanted: Align) -> Integer {
 527         let dl = cx.data_layout();
 528
 529         // FIXME(eddyb) maybe include I128 in the future, when it works everywhere.
 530         for &candidate in &[I64, I32, I16] {
 531             if wanted >= candidate.align(dl).abi && wanted.bytes() >= candidate.size().bytes() {
 532                 return candidate;
 533             }
 534         }
 535         I8
 536     }
 537 }
 538
 539 /// Fundamental unit of memory access and layout.
 540 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 541 pub enum Primitive {
 542     /// The `bool` is the signedness of the `Integer` type.
 543     ///
 544     /// One would think we would not care about such details this low down,
 545     /// but some ABIs are described in terms of C types and ISAs where the
 546     /// integer arithmetic is done on {sign,zero}-extended registers, e.g.
 547     /// a negative integer passed by zero-extension will appear positive in
 548     /// the callee, and most operations on it will produce the wrong values.
 549     Int(Integer, bool),
 550     F32,
 551     F64,
 552     Pointer
 553 }
 554
 555 impl Primitive {
 556     pub fn size<C: HasDataLayout>(self, cx: &C) -> Size {
 557         let dl = cx.data_layout();
 558
 559         match self {
 560             Int(i, _) => i.size(),
 561             F32 => Size::from_bits(32),
 562             F64 => Size::from_bits(64),
 563             Pointer => dl.pointer_size
 564         }
 565     }
 566
 567     pub fn align<C: HasDataLayout>(self, cx: &C) -> AbiAndPrefAlign {
 568         let dl = cx.data_layout();
 569
 570         match self {
 571             Int(i, _) => i.align(dl),
 572             F32 => dl.f32_align,
 573             F64 => dl.f64_align,
 574             Pointer => dl.pointer_align
 575         }
 576     }
 577
 578     pub fn is_float(self) -> bool {
 579         match self {
 580             F32 | F64 => true,
 581             _ => false
 582         }
 583     }
 584
 585     pub fn is_int(self) -> bool {
 586         match self {
 587             Int(..) => true,
 588             _ => false,
 589         }
 590     }
 591 }
 592
 593 /// Information about one scalar component of a Rust type.
 594 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
 595 #[derive(HashStable_Generic)]
 596 pub struct Scalar {
 597     pub value: Primitive,
 598
 599     /// Inclusive wrap-around range of valid values, that is, if
 600     /// start > end, it represents `start..=max_value()`,
 601     /// followed by `0..=end`.
 602     ///
 603     /// That is, for an i8 primitive, a range of `254..=2` means following
 604     /// sequence:
 605     ///
 606     ///    254 (-2), 255 (-1), 0, 1, 2
 607     ///
 608     /// This is intended specifically to mirror LLVM’s `!range` metadata,
 609     /// semantics.
 610     // FIXME(eddyb) always use the shortest range, e.g., by finding
 611     // the largest space between two consecutive valid values and
 612     // taking everything else as the (shortest) valid range.
 613     pub valid_range: RangeInclusive<u128>,
 614 }
 615
 616 impl Scalar {
 617     pub fn is_bool(&self) -> bool {
 618         if let Int(I8, _) = self.value {
 619             self.valid_range == (0..=1)
 620         } else {
 621             false
 622         }
 623     }
 624
 625     /// Returns the valid range as a `x..y` range.
 626     ///
 627     /// If `x` and `y` are equal, the range is full, not empty.
 628     pub fn valid_range_exclusive<C: HasDataLayout>(&self, cx: &C) -> Range<u128> {
 629         // For a (max) value of -1, max will be `-1 as usize`, which overflows.
 630         // However, that is fine here (it would still represent the full range),
 631         // i.e., if the range is everything.
 632         let bits = self.value.size(cx).bits();
 633         assert!(bits <= 128);
 634         let mask = !0u128 >> (128 - bits);
 635         let start = *self.valid_range.start();
 636         let end = *self.valid_range.end();
 637         assert_eq!(start, start & mask);
 638         assert_eq!(end, end & mask);
 639         start..(end.wrapping_add(1) & mask)
 640     }
 641 }
 642
 643 /// Describes how the fields of a type are located in memory.
 644 #[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 645 pub enum FieldPlacement {
 646     /// All fields start at no offset. The `usize` is the field count.
 647     ///
 648     /// In the case of primitives the number of fields is `0`.
 649     Union(usize),
 650
 651     /// Array/vector-like placement, with all fields of identical types.
 652     Array {
 653         stride: Size,
 654         count: u64
 655     },
 656
 657     /// Struct-like placement, with precomputed offsets.
 658     ///
 659     /// Fields are guaranteed to not overlap, but note that gaps
 660     /// before, between and after all the fields are NOT always
 661     /// padding, and as such their contents may not be discarded.
 662     /// For example, enum variants leave a gap at the start,
 663     /// where the discriminant field in the enum layout goes.
 664     Arbitrary {
 665         /// Offsets for the first byte of each field,
 666         /// ordered to match the source definition order.
 667         /// This vector does not go in increasing order.
 668         // FIXME(eddyb) use small vector optimization for the common case.
 669         offsets: Vec<Size>,
 670
 671         /// Maps source order field indices to memory order indices,
 672         /// depending on how the fields were reordered (if at all).
 673         /// This is a permutation, with both the source order and the
 674         /// memory order using the same (0..n) index ranges.
 675         ///
 676         /// Note that during computation of `memory_index`, sometimes
 677         /// it is easier to operate on the inverse mapping (that is,
 678         /// from memory order to source order), and that is usually
 679         /// named `inverse_memory_index`.
 680         ///
 681         // FIXME(eddyb) build a better abstraction for permutations, if possible.
 682         // FIXME(camlorn) also consider small vector  optimization here.
 683         memory_index: Vec<u32>
 684     }
 685 }
 686
 687 impl FieldPlacement {
 688     pub fn count(&self) -> usize {
 689         match *self {
 690             FieldPlacement::Union(count) => count,
 691             FieldPlacement::Array { count, .. } => {
 692                 let usize_count = count as usize;
 693                 assert_eq!(usize_count as u64, count);
 694                 usize_count
 695             }
 696             FieldPlacement::Arbitrary { ref offsets, .. } => offsets.len()
 697         }
 698     }
 699
 700     pub fn offset(&self, i: usize) -> Size {
 701         match *self {
 702             FieldPlacement::Union(_) => Size::ZERO,
 703             FieldPlacement::Array { stride, count } => {
 704                 let i = i as u64;
 705                 assert!(i < count);
 706                 stride * i
 707             }
 708             FieldPlacement::Arbitrary { ref offsets, .. } => offsets[i]
 709         }
 710     }
 711
 712     pub fn memory_index(&self, i: usize) -> usize {
 713         match *self {
 714             FieldPlacement::Union(_) |
 715             FieldPlacement::Array { .. } => i,
 716             FieldPlacement::Arbitrary { ref memory_index, .. } => {
 717                 let r = memory_index[i];
 718                 assert_eq!(r as usize as u32, r);
 719                 r as usize
 720             }
 721         }
 722     }
 723
 724     /// Gets source indices of the fields by increasing offsets.
 725     #[inline]
 726     pub fn index_by_increasing_offset<'a>(&'a self) -> impl Iterator<Item=usize>+'a {
 727         let mut inverse_small = [0u8; 64];
 728         let mut inverse_big = vec![];
 729         let use_small = self.count() <= inverse_small.len();
 730
 731         // We have to write this logic twice in order to keep the array small.
 732         if let FieldPlacement::Arbitrary { ref memory_index, .. } = *self {
 733             if use_small {
 734                 for i in 0..self.count() {
 735                     inverse_small[memory_index[i] as usize] = i as u8;
 736                 }
 737             } else {
 738                 inverse_big = vec![0; self.count()];
 739                 for i in 0..self.count() {
 740                     inverse_big[memory_index[i] as usize] = i as u32;
 741                 }
 742             }
 743         }
 744
 745         (0..self.count()).map(move |i| {
 746             match *self {
 747                 FieldPlacement::Union(_) |
 748                 FieldPlacement::Array { .. } => i,
 749                 FieldPlacement::Arbitrary { .. } => {
 750                     if use_small { inverse_small[i] as usize }
 751                     else { inverse_big[i] as usize }
 752                 }
 753             }
 754         })
 755     }
 756 }
 757
 758 /// Describes how values of the type are passed by target ABIs,
 759 /// in terms of categories of C types there are ABI rules for.
 760 #[derive(Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 761 pub enum Abi {
 762     Uninhabited,
 763     Scalar(Scalar),
 764     ScalarPair(Scalar, Scalar),
 765     Vector {
 766         element: Scalar,
 767         count: u64
 768     },
 769     Aggregate {
 770         /// If true, the size is exact, otherwise it's only a lower bound.
 771         sized: bool,
 772     }
 773 }
 774
 775 impl Abi {
 776     /// Returns `true` if the layout corresponds to an unsized type.
 777     pub fn is_unsized(&self) -> bool {
 778         match *self {
 779             Abi::Uninhabited |
 780             Abi::Scalar(_) |
 781             Abi::ScalarPair(..) |
 782             Abi::Vector { .. } => false,
 783             Abi::Aggregate { sized } => !sized
 784         }
 785     }
 786
 787     /// Returns `true` if this is a single signed integer scalar
 788     pub fn is_signed(&self) -> bool {
 789         match *self {
 790             Abi::Scalar(ref scal) => match scal.value {
 791                 Primitive::Int(_, signed) => signed,
 792                 _ => false,
 793             },
 794             _ => false,
 795         }
 796     }
 797
 798     /// Returns `true` if this is an uninhabited type
 799     pub fn is_uninhabited(&self) -> bool {
 800         match *self {
 801             Abi::Uninhabited => true,
 802             _ => false,
 803         }
 804     }
 805
 806     /// Returns `true` is this is a scalar type
 807     pub fn is_scalar(&self) -> bool {
 808         match *self {
 809             Abi::Scalar(_) => true,
 810             _ => false,
 811         }
 812     }
 813 }
 814
 815 rustc_index::newtype_index! {
 816     pub struct VariantIdx {
 817         derive [HashStable_Generic]
 818     }
 819 }
 820
 821 #[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 822 pub enum Variants {
 823     /// Single enum variants, structs/tuples, unions, and all non-ADTs.
 824     Single {
 825         index: VariantIdx,
 826     },
 827
 828     /// Enum-likes with more than one inhabited variant: for each case there is
 829     /// a struct, and they all have space reserved for the discriminant.
 830     /// For enums this is the sole field of the layout.
 831     Multiple {
 832         discr: Scalar,
 833         discr_kind: DiscriminantKind,
 834         discr_index: usize,
 835         variants: IndexVec<VariantIdx, LayoutDetails>,
 836     },
 837 }
 838
 839 #[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 840 pub enum DiscriminantKind {
 841     /// Integer tag holding the discriminant value itself.
 842     Tag,
 843
 844     /// Niche (values invalid for a type) encoding the discriminant:
 845     /// the variant `dataful_variant` contains a niche at an arbitrary
 846     /// offset (field `discr_index` of the enum), which for a variant with
 847     /// discriminant `d` is set to
 848     /// `(d - niche_variants.start).wrapping_add(niche_start)`.
 849     ///
 850     /// For example, `Option<(usize, &T)>`  is represented such that
 851     /// `None` has a null pointer for the second tuple field, and
 852     /// `Some` is the identity function (with a non-null reference).
 853     Niche {
 854         dataful_variant: VariantIdx,
 855         niche_variants: RangeInclusive<VariantIdx>,
 856         niche_start: u128,
 857     },
 858 }
 859
 860 #[derive(Clone, PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 861 pub struct Niche {
 862     pub offset: Size,
 863     pub scalar: Scalar,
 864 }
 865
 866 impl Niche {
 867     pub fn from_scalar<C: HasDataLayout>(cx: &C, offset: Size, scalar: Scalar) -> Option<Self> {
 868         let niche = Niche {
 869             offset,
 870             scalar,
 871         };
 872         if niche.available(cx) > 0 {
 873             Some(niche)
 874         } else {
 875             None
 876         }
 877     }
 878
 879     pub fn available<C: HasDataLayout>(&self, cx: &C) -> u128 {
 880         let Scalar { value, valid_range: ref v } = self.scalar;
 881         let bits = value.size(cx).bits();
 882         assert!(bits <= 128);
 883         let max_value = !0u128 >> (128 - bits);
 884
 885         // Find out how many values are outside the valid range.
 886         let niche = v.end().wrapping_add(1)..*v.start();
 887         niche.end.wrapping_sub(niche.start) & max_value
 888     }
 889
 890     pub fn reserve<C: HasDataLayout>(&self, cx: &C, count: u128) -> Option<(u128, Scalar)> {
 891         assert!(count > 0);
 892
 893         let Scalar { value, valid_range: ref v } = self.scalar;
 894         let bits = value.size(cx).bits();
 895         assert!(bits <= 128);
 896         let max_value = !0u128 >> (128 - bits);
 897
 898         if count > max_value {
 899             return None;
 900         }
 901
 902         // Compute the range of invalid values being reserved.
 903         let start = v.end().wrapping_add(1) & max_value;
 904         let end = v.end().wrapping_add(count) & max_value;
 905
 906         // If the `end` of our range is inside the valid range,
 907         // then we ran out of invalid values.
 908         // FIXME(eddyb) abstract this with a wraparound range type.
 909         let valid_range_contains = |x| {
 910             if v.start() <= v.end() {
 911                 *v.start() <= x && x <= *v.end()
 912             } else {
 913                 *v.start() <= x || x <= *v.end()
 914             }
 915         };
 916         if valid_range_contains(end) {
 917             return None;
 918         }
 919
 920         Some((start, Scalar { value, valid_range: *v.start()..=end }))
 921     }
 922 }
 923
 924 #[derive(PartialEq, Eq, Hash, Debug, HashStable_Generic)]
 925 pub struct LayoutDetails {
 926     pub variants: Variants,
 927     pub fields: FieldPlacement,
 928     pub abi: Abi,
 929
 930     /// The leaf scalar with the largest number of invalid values
 931     /// (i.e. outside of its `valid_range`), if it exists.
 932     pub largest_niche: Option<Niche>,
 933
 934     pub align: AbiAndPrefAlign,
 935     pub size: Size
 936 }
 937
 938 impl LayoutDetails {
 939     pub fn scalar<C: HasDataLayout>(cx: &C, scalar: Scalar) -> Self {
 940         let largest_niche = Niche::from_scalar(cx, Size::ZERO, scalar.clone());
 941         let size = scalar.value.size(cx);
 942         let align = scalar.value.align(cx);
 943         LayoutDetails {
 944             variants: Variants::Single { index: VariantIdx::new(0) },
 945             fields: FieldPlacement::Union(0),
 946             abi: Abi::Scalar(scalar),
 947             largest_niche,
 948             size,
 949             align,
 950         }
 951     }
 952 }
 953
 954 /// The details of the layout of a type, alongside the type itself.
 955 /// Provides various type traversal APIs (e.g., recursing into fields).
 956 ///
 957 /// Note that the details are NOT guaranteed to always be identical
 958 /// to those obtained from `layout_of(ty)`, as we need to produce
 959 /// layouts for which Rust types do not exist, such as enum variants
 960 /// or synthetic fields of enums (i.e., discriminants) and fat pointers.
 961 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 962 pub struct TyLayout<'a, Ty> {
 963     pub ty: Ty,
 964     pub details: &'a LayoutDetails
 965 }
 966
 967 impl<'a, Ty> Deref for TyLayout<'a, Ty> {
 968     type Target = &'a LayoutDetails;
 969     fn deref(&self) -> &&'a LayoutDetails {
 970         &self.details
 971     }
 972 }
 973
 974 pub trait LayoutOf {
 975     type Ty;
 976     type TyLayout;
 977
 978     fn layout_of(&self, ty: Self::Ty) -> Self::TyLayout;
 979     fn spanned_layout_of(&self, ty: Self::Ty, _span: Span) -> Self::TyLayout {
 980         self.layout_of(ty)
 981     }
 982 }
 983
 984 #[derive(Copy, Clone, PartialEq, Eq)]
 985 pub enum PointerKind {
 986     /// Most general case, we know no restrictions to tell LLVM.
 987     Shared,
 988
 989     /// `&T` where `T` contains no `UnsafeCell`, is `noalias` and `readonly`.
 990     Frozen,
 991
 992     /// `&mut T`, when we know `noalias` is safe for LLVM.
 993     UniqueBorrowed,
 994
 995     /// `Box<T>`, unlike `UniqueBorrowed`, it also has `noalias` on returns.
 996     UniqueOwned
 997 }
 998
 999 #[derive(Copy, Clone)]
1000 pub struct PointeeInfo {
1001     pub size: Size,
1002     pub align: Align,
1003     pub safe: Option<PointerKind>,
1004 }
1005
1006 pub trait TyLayoutMethods<'a, C: LayoutOf<Ty = Self>>: Sized {
1007     fn for_variant(
1008         this: TyLayout<'a, Self>,
1009         cx: &C,
1010         variant_index: VariantIdx,
1011     ) -> TyLayout<'a, Self>;
1012     fn field(this: TyLayout<'a, Self>, cx: &C, i: usize) -> C::TyLayout;
1013     fn pointee_info_at(
1014         this: TyLayout<'a, Self>,
1015         cx: &C,
1016         offset: Size,
1017     ) -> Option<PointeeInfo>;
1018 }
1019
1020 impl<'a, Ty> TyLayout<'a, Ty> {
1021     pub fn for_variant<C>(self, cx: &C, variant_index: VariantIdx) -> Self
1022     where Ty: TyLayoutMethods<'a, C>, C: LayoutOf<Ty = Ty> {
1023         Ty::for_variant(self, cx, variant_index)
1024     }
1025     pub fn field<C>(self, cx: &C, i: usize) -> C::TyLayout
1026     where Ty: TyLayoutMethods<'a, C>, C: LayoutOf<Ty = Ty> {
1027         Ty::field(self, cx, i)
1028     }
1029     pub fn pointee_info_at<C>(self, cx: &C, offset: Size) -> Option<PointeeInfo>
1030     where Ty: TyLayoutMethods<'a, C>, C: LayoutOf<Ty = Ty> {
1031         Ty::pointee_info_at(self, cx, offset)
1032     }
1033 }
1034
1035 impl<'a, Ty> TyLayout<'a, Ty> {
1036     /// Returns `true` if the layout corresponds to an unsized type.
1037     pub fn is_unsized(&self) -> bool {
1038         self.abi.is_unsized()
1039     }
1040
1041     /// Returns `true` if the type is a ZST and not unsized.
1042     pub fn is_zst(&self) -> bool {
1043         match self.abi {
1044             Abi::Scalar(_) |
1045             Abi::ScalarPair(..) |
1046             Abi::Vector { .. } => false,
1047             Abi::Uninhabited => self.size.bytes() == 0,
1048             Abi::Aggregate { sized } => sized && self.size.bytes() == 0
1049         }
1050     }
1051 }