src/librustc_mir_build/thir/mod.rs

   1 //! The MIR is built from some typed high-level IR
   2 //! (THIR). This section defines the THIR along with a trait for
   3 //! accessing it. The intention is to allow MIR construction to be
   4 //! unit-tested and separated from the Rust source and compiler data
   5 //! structures.
   6
   7 use self::cx::Cx;
   8 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
   9 use rustc_hir as hir;
  10 use rustc_hir::def_id::DefId;
  11 use rustc_middle::infer::canonical::Canonical;
  12 use rustc_middle::middle::region;
  13 use rustc_middle::mir::{BinOp, BorrowKind, Field, UnOp};
  14 use rustc_middle::ty::adjustment::PointerCast;
  15 use rustc_middle::ty::subst::SubstsRef;
  16 use rustc_middle::ty::{AdtDef, Const, Ty, UpvarSubsts, UserType};
  17 use rustc_span::Span;
  18 use rustc_target::abi::VariantIdx;
  19 use rustc_target::asm::InlineAsmRegOrRegClass;
  20
  21 crate mod constant;
  22 crate mod cx;
  23
  24 crate mod pattern;
  25 crate use self::pattern::PatTyProj;
  26 crate use self::pattern::{BindingMode, FieldPat, Pat, PatKind, PatRange};
  27
  28 mod util;
  29
  30 #[derive(Copy, Clone, Debug)]
  31 crate enum LintLevel {
  32     Inherited,
  33     Explicit(hir::HirId),
  34 }
  35
  36 #[derive(Clone, Debug)]
  37 crate struct Block<'tcx> {
  38     crate targeted_by_break: bool,
  39     crate region_scope: region::Scope,
  40     crate opt_destruction_scope: Option<region::Scope>,
  41     crate span: Span,
  42     crate stmts: Vec<StmtRef<'tcx>>,
  43     crate expr: Option<ExprRef<'tcx>>,
  44     crate safety_mode: BlockSafety,
  45 }
  46
  47 #[derive(Copy, Clone, Debug)]
  48 crate enum BlockSafety {
  49     Safe,
  50     ExplicitUnsafe(hir::HirId),
  51     PushUnsafe,
  52     PopUnsafe,
  53 }
  54
  55 #[derive(Clone, Debug)]
  56 crate enum StmtRef<'tcx> {
  57     Mirror(Box<Stmt<'tcx>>),
  58 }
  59
  60 #[derive(Clone, Debug)]
  61 crate struct Stmt<'tcx> {
  62     crate kind: StmtKind<'tcx>,
  63     crate opt_destruction_scope: Option<region::Scope>,
  64 }
  65
  66 #[derive(Clone, Debug)]
  67 crate enum StmtKind<'tcx> {
  68     Expr {
  69         /// scope for this statement; may be used as lifetime of temporaries
  70         scope: region::Scope,
  71
  72         /// expression being evaluated in this statement
  73         expr: ExprRef<'tcx>,
  74     },
  75
  76     Let {
  77         /// scope for variables bound in this let; covers this and
  78         /// remaining statements in block
  79         remainder_scope: region::Scope,
  80
  81         /// scope for the initialization itself; might be used as
  82         /// lifetime of temporaries
  83         init_scope: region::Scope,
  84
  85         /// `let <PAT> = ...`
  86         ///
  87         /// if a type is included, it is added as an ascription pattern
  88         pattern: Pat<'tcx>,
  89
  90         /// let pat: ty = <INIT> ...
  91         initializer: Option<ExprRef<'tcx>>,
  92
  93         /// the lint level for this let-statement
  94         lint_level: LintLevel,
  95     },
  96 }
  97
  98 // `Expr` is used a lot. Make sure it doesn't unintentionally get bigger.
  99 #[cfg(target_arch = "x86_64")]
 100 rustc_data_structures::static_assert_size!(Expr<'_>, 168);
 101
 102 /// The Thir trait implementor lowers their expressions (`&'tcx H::Expr`)
 103 /// into instances of this `Expr` enum. This lowering can be done
 104 /// basically as lazily or as eagerly as desired: every recursive
 105 /// reference to an expression in this enum is an `ExprRef<'tcx>`, which
 106 /// may in turn be another instance of this enum (boxed), or else an
 107 /// unlowered `&'tcx H::Expr`. Note that instances of `Expr` are very
 108 /// short-lived. They are created by `Thir::to_expr`, analyzed and
 109 /// converted into MIR, and then discarded.
 110 ///
 111 /// If you compare `Expr` to the full compiler AST, you will see it is
 112 /// a good bit simpler. In fact, a number of the more straight-forward
 113 /// MIR simplifications are already done in the impl of `Thir`. For
 114 /// example, method calls and overloaded operators are absent: they are
 115 /// expected to be converted into `Expr::Call` instances.
 116 #[derive(Clone, Debug)]
 117 crate struct Expr<'tcx> {
 118     /// type of this expression
 119     crate ty: Ty<'tcx>,
 120
 121     /// lifetime of this expression if it should be spilled into a
 122     /// temporary; should be None only if in a constant context
 123     crate temp_lifetime: Option<region::Scope>,
 124
 125     /// span of the expression in the source
 126     crate span: Span,
 127
 128     /// kind of expression
 129     crate kind: ExprKind<'tcx>,
 130 }
 131
 132 #[derive(Clone, Debug)]
 133 crate enum ExprKind<'tcx> {
 134     Scope {
 135         region_scope: region::Scope,
 136         lint_level: LintLevel,
 137         value: ExprRef<'tcx>,
 138     },
 139     Box {
 140         value: ExprRef<'tcx>,
 141     },
 142     Call {
 143         ty: Ty<'tcx>,
 144         fun: ExprRef<'tcx>,
 145         args: Vec<ExprRef<'tcx>>,
 146         // Whether this is from a call in HIR, rather than from an overloaded
 147         // operator. True for overloaded function call.
 148         from_hir_call: bool,
 149         /// This `Span` is the span of the function, without the dot and receiver
 150         /// (e.g. `foo(a, b)` in `x.foo(a, b)`
 151         fn_span: Span,
 152     },
 153     Deref {
 154         arg: ExprRef<'tcx>,
 155     }, // NOT overloaded!
 156     Binary {
 157         op: BinOp,
 158         lhs: ExprRef<'tcx>,
 159         rhs: ExprRef<'tcx>,
 160     }, // NOT overloaded!
 161     LogicalOp {
 162         op: LogicalOp,
 163         lhs: ExprRef<'tcx>,
 164         rhs: ExprRef<'tcx>,
 165     }, // NOT overloaded!
 166     // LogicalOp is distinct from BinaryOp because of lazy evaluation of the operands.
 167     Unary {
 168         op: UnOp,
 169         arg: ExprRef<'tcx>,
 170     }, // NOT overloaded!
 171     Cast {
 172         source: ExprRef<'tcx>,
 173     },
 174     Use {
 175         source: ExprRef<'tcx>,
 176     }, // Use a lexpr to get a vexpr.
 177     NeverToAny {
 178         source: ExprRef<'tcx>,
 179     },
 180     Pointer {
 181         cast: PointerCast,
 182         source: ExprRef<'tcx>,
 183     },
 184     Loop {
 185         body: ExprRef<'tcx>,
 186     },
 187     Match {
 188         scrutinee: ExprRef<'tcx>,
 189         arms: Vec<Arm<'tcx>>,
 190     },
 191     Block {
 192         body: &'tcx hir::Block<'tcx>,
 193     },
 194     Assign {
 195         lhs: ExprRef<'tcx>,
 196         rhs: ExprRef<'tcx>,
 197     },
 198     AssignOp {
 199         op: BinOp,
 200         lhs: ExprRef<'tcx>,
 201         rhs: ExprRef<'tcx>,
 202     },
 203     Field {
 204         lhs: ExprRef<'tcx>,
 205         name: Field,
 206     },
 207     Index {
 208         lhs: ExprRef<'tcx>,
 209         index: ExprRef<'tcx>,
 210     },
 211     VarRef {
 212         id: hir::HirId,
 213     },
 214     /// first argument, used for self in a closure
 215     SelfRef,
 216     Borrow {
 217         borrow_kind: BorrowKind,
 218         arg: ExprRef<'tcx>,
 219     },
 220     /// A `&raw [const|mut] $place_expr` raw borrow resulting in type `*[const|mut] T`.
 221     AddressOf {
 222         mutability: hir::Mutability,
 223         arg: ExprRef<'tcx>,
 224     },
 225     Break {
 226         label: region::Scope,
 227         value: Option<ExprRef<'tcx>>,
 228     },
 229     Continue {
 230         label: region::Scope,
 231     },
 232     Return {
 233         value: Option<ExprRef<'tcx>>,
 234     },
 235     Repeat {
 236         value: ExprRef<'tcx>,
 237         count: &'tcx Const<'tcx>,
 238     },
 239     Array {
 240         fields: Vec<ExprRef<'tcx>>,
 241     },
 242     Tuple {
 243         fields: Vec<ExprRef<'tcx>>,
 244     },
 245     Adt {
 246         adt_def: &'tcx AdtDef,
 247         variant_index: VariantIdx,
 248         substs: SubstsRef<'tcx>,
 249
 250         /// Optional user-given substs: for something like `let x =
 251         /// Bar::<T> { ... }`.
 252         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
 253
 254         fields: Vec<FieldExprRef<'tcx>>,
 255         base: Option<FruInfo<'tcx>>,
 256     },
 257     PlaceTypeAscription {
 258         source: ExprRef<'tcx>,
 259         /// Type that the user gave to this expression
 260         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
 261     },
 262     ValueTypeAscription {
 263         source: ExprRef<'tcx>,
 264         /// Type that the user gave to this expression
 265         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
 266     },
 267     Closure {
 268         closure_id: DefId,
 269         substs: UpvarSubsts<'tcx>,
 270         upvars: Vec<ExprRef<'tcx>>,
 271         movability: Option<hir::Movability>,
 272     },
 273     Literal {
 274         literal: &'tcx Const<'tcx>,
 275         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
 276     },
 277     /// A literal containing the address of a `static`.
 278     ///
 279     /// This is only distinguished from `Literal` so that we can register some
 280     /// info for diagnostics.
 281     StaticRef {
 282         literal: &'tcx Const<'tcx>,
 283         def_id: DefId,
 284     },
 285     InlineAsm {
 286         template: &'tcx [InlineAsmTemplatePiece],
 287         operands: Vec<InlineAsmOperand<'tcx>>,
 288         options: InlineAsmOptions,
 289         line_spans: &'tcx [Span],
 290     },
 291     /// An expression taking a reference to a thread local.
 292     ThreadLocalRef(DefId),
 293     LlvmInlineAsm {
 294         asm: &'tcx hir::LlvmInlineAsmInner,
 295         outputs: Vec<ExprRef<'tcx>>,
 296         inputs: Vec<ExprRef<'tcx>>,
 297     },
 298     Yield {
 299         value: ExprRef<'tcx>,
 300     },
 301 }
 302
 303 #[derive(Clone, Debug)]
 304 crate enum ExprRef<'tcx> {
 305     Thir(&'tcx hir::Expr<'tcx>),
 306     Mirror(Box<Expr<'tcx>>),
 307 }
 308
 309 #[derive(Clone, Debug)]
 310 crate struct FieldExprRef<'tcx> {
 311     crate name: Field,
 312     crate expr: ExprRef<'tcx>,
 313 }
 314
 315 #[derive(Clone, Debug)]
 316 crate struct FruInfo<'tcx> {
 317     crate base: ExprRef<'tcx>,
 318     crate field_types: Vec<Ty<'tcx>>,
 319 }
 320
 321 #[derive(Clone, Debug)]
 322 crate struct Arm<'tcx> {
 323     crate pattern: Pat<'tcx>,
 324     crate guard: Option<Guard<'tcx>>,
 325     crate body: ExprRef<'tcx>,
 326     crate lint_level: LintLevel,
 327     crate scope: region::Scope,
 328     crate span: Span,
 329 }
 330
 331 #[derive(Clone, Debug)]
 332 crate enum Guard<'tcx> {
 333     If(ExprRef<'tcx>),
 334 }
 335
 336 #[derive(Copy, Clone, Debug)]
 337 crate enum LogicalOp {
 338     And,
 339     Or,
 340 }
 341
 342 impl<'tcx> ExprRef<'tcx> {
 343     crate fn span(&self) -> Span {
 344         match self {
 345             ExprRef::Thir(expr) => expr.span,
 346             ExprRef::Mirror(expr) => expr.span,
 347         }
 348     }
 349 }
 350
 351 #[derive(Clone, Debug)]
 352 crate enum InlineAsmOperand<'tcx> {
 353     In {
 354         reg: InlineAsmRegOrRegClass,
 355         expr: ExprRef<'tcx>,
 356     },
 357     Out {
 358         reg: InlineAsmRegOrRegClass,
 359         late: bool,
 360         expr: Option<ExprRef<'tcx>>,
 361     },
 362     InOut {
 363         reg: InlineAsmRegOrRegClass,
 364         late: bool,
 365         expr: ExprRef<'tcx>,
 366     },
 367     SplitInOut {
 368         reg: InlineAsmRegOrRegClass,
 369         late: bool,
 370         in_expr: ExprRef<'tcx>,
 371         out_expr: Option<ExprRef<'tcx>>,
 372     },
 373     Const {
 374         expr: ExprRef<'tcx>,
 375     },
 376     SymFn {
 377         expr: ExprRef<'tcx>,
 378     },
 379     SymStatic {
 380         def_id: DefId,
 381     },
 382 }
 383
 384 ///////////////////////////////////////////////////////////////////////////
 385 // The Mirror trait
 386
 387 /// "Mirroring" is the process of converting from a HIR type into one
 388 /// of the THIR types defined in this file. This is basically a "on
 389 /// the fly" desugaring step that hides a lot of the messiness in the
 390 /// tcx. For example, the mirror of a `&'tcx hir::Expr` is an
 391 /// `Expr<'tcx>`.
 392 ///
 393 /// Mirroring is gradual: when you mirror an outer expression like `e1
 394 /// + e2`, the references to the inner expressions `e1` and `e2` are
 395 /// `ExprRef<'tcx>` instances, and they may or may not be eagerly
 396 /// mirrored. This allows a single AST node from the compiler to
 397 /// expand into one or more Thir nodes, which lets the Thir nodes be
 398 /// simpler.
 399 crate trait Mirror<'tcx> {
 400     type Output;
 401
 402     fn make_mirror(self, cx: &mut Cx<'_, 'tcx>) -> Self::Output;
 403 }
 404
 405 impl<'tcx> Mirror<'tcx> for Expr<'tcx> {
 406     type Output = Expr<'tcx>;
 407
 408     fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Expr<'tcx> {
 409         self
 410     }
 411 }
 412
 413 impl<'tcx> Mirror<'tcx> for ExprRef<'tcx> {
 414     type Output = Expr<'tcx>;
 415
 416     fn make_mirror(self, hir: &mut Cx<'_, 'tcx>) -> Expr<'tcx> {
 417         match self {
 418             ExprRef::Thir(h) => h.make_mirror(hir),
 419             ExprRef::Mirror(m) => *m,
 420         }
 421     }
 422 }
 423
 424 impl<'tcx> Mirror<'tcx> for Stmt<'tcx> {
 425     type Output = Stmt<'tcx>;
 426
 427     fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Stmt<'tcx> {
 428         self
 429     }
 430 }
 431
 432 impl<'tcx> Mirror<'tcx> for StmtRef<'tcx> {
 433     type Output = Stmt<'tcx>;
 434
 435     fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Stmt<'tcx> {
 436         match self {
 437             StmtRef::Mirror(m) => *m,
 438         }
 439     }
 440 }
 441
 442 impl<'tcx> Mirror<'tcx> for Block<'tcx> {
 443     type Output = Block<'tcx>;
 444
 445     fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Block<'tcx> {
 446         self
 447     }
 448 }