src/librustc_mir/build/expr/as_rvalue.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! See docs in build/expr/mod.rs
  12
  13 use std;
  14
  15 use rustc_const_math::{ConstMathErr, Op};
  16 use rustc_data_structures::fx::FxHashMap;
  17 use rustc_data_structures::indexed_vec::Idx;
  18
  19 use build::{BlockAnd, BlockAndExtension, Builder};
  20 use build::expr::category::{Category, RvalueFunc};
  21 use hair::*;
  22 use rustc_const_math::{ConstInt, ConstIsize};
  23 use rustc::middle::const_val::ConstVal;
  24 use rustc::middle::region;
  25 use rustc::ty::{self, Ty};
  26 use rustc::mir::*;
  27 use rustc::mir::interpret::{Value, PrimVal};
  28 use syntax::ast;
  29 use syntax_pos::Span;
  30
  31 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  32     /// See comment on `as_local_operand`
  33     pub fn as_local_rvalue<M>(&mut self, block: BasicBlock, expr: M)
  34                              -> BlockAnd<Rvalue<'tcx>>
  35         where M: Mirror<'tcx, Output = Expr<'tcx>>
  36     {
  37         let local_scope = self.local_scope();
  38         self.as_rvalue(block, local_scope, expr)
  39     }
  40
  41     /// Compile `expr`, yielding an rvalue.
  42     pub fn as_rvalue<M>(&mut self, block: BasicBlock, scope: Option<region::Scope>, expr: M)
  43                         -> BlockAnd<Rvalue<'tcx>>
  44         where M: Mirror<'tcx, Output = Expr<'tcx>>
  45     {
  46         let expr = self.hir.mirror(expr);
  47         self.expr_as_rvalue(block, scope, expr)
  48     }
  49
  50     fn expr_as_rvalue(&mut self,
  51                       mut block: BasicBlock,
  52                       scope: Option<region::Scope>,
  53                       expr: Expr<'tcx>)
  54                       -> BlockAnd<Rvalue<'tcx>> {
  55         debug!("expr_as_rvalue(block={:?}, scope={:?}, expr={:?})", block, scope, expr);
  56
  57         let this = self;
  58         let expr_span = expr.span;
  59         let source_info = this.source_info(expr_span);
  60
  61         match expr.kind {
  62             ExprKind::Scope { region_scope, lint_level, value } => {
  63                 let region_scope = (region_scope, source_info);
  64                 this.in_scope(region_scope, lint_level, block,
  65                               |this| this.as_rvalue(block, scope, value))
  66             }
  67             ExprKind::Repeat { value, count } => {
  68                 let value_operand = unpack!(block = this.as_operand(block, scope, value));
  69                 block.and(Rvalue::Repeat(value_operand, count))
  70             }
  71             ExprKind::Borrow { region, borrow_kind, arg } => {
  72                 let arg_place = unpack!(block = this.as_place(block, arg));
  73                 block.and(Rvalue::Ref(region, borrow_kind, arg_place))
  74             }
  75             ExprKind::Binary { op, lhs, rhs } => {
  76                 let lhs = unpack!(block = this.as_operand(block, scope, lhs));
  77                 let rhs = unpack!(block = this.as_operand(block, scope, rhs));
  78                 this.build_binary_op(block, op, expr_span, expr.ty,
  79                                      lhs, rhs)
  80             }
  81             ExprKind::Unary { op, arg } => {
  82                 let arg = unpack!(block = this.as_operand(block, scope, arg));
  83                 // Check for -MIN on signed integers
  84                 if this.hir.check_overflow() && op == UnOp::Neg && expr.ty.is_signed() {
  85                     let bool_ty = this.hir.bool_ty();
  86
  87                     let minval = this.minval_literal(expr_span, expr.ty);
  88                     let is_min = this.temp(bool_ty, expr_span);
  89
  90                     this.cfg.push_assign(block, source_info, &is_min,
  91                                          Rvalue::BinaryOp(BinOp::Eq, arg.to_copy(), minval));
  92
  93                     let err = ConstMathErr::Overflow(Op::Neg);
  94                     block = this.assert(block, Operand::Move(is_min), false,
  95                                         AssertMessage::Math(err), expr_span);
  96                 }
  97                 block.and(Rvalue::UnaryOp(op, arg))
  98             }
  99             ExprKind::Box { value } => {
 100                 let value = this.hir.mirror(value);
 101                 // The `Box<T>` temporary created here is not a part of the HIR,
 102                 // and therefore is not considered during generator OIBIT
 103                 // determination. See the comment about `box` at `yield_in_scope`.
 104                 let result = this.local_decls.push(
 105                     LocalDecl::new_internal(expr.ty, expr_span));
 106                 this.cfg.push(block, Statement {
 107                     source_info,
 108                     kind: StatementKind::StorageLive(result)
 109                 });
 110                 if let Some(scope) = scope {
 111                     // schedule a shallow free of that memory, lest we unwind:
 112                     this.schedule_drop(expr_span, scope, &Place::Local(result), value.ty);
 113                 }
 114
 115                 // malloc some memory of suitable type (thus far, uninitialized):
 116                 let box_ = Rvalue::NullaryOp(NullOp::Box, value.ty);
 117                 this.cfg.push_assign(block, source_info, &Place::Local(result), box_);
 118
 119                 // initialize the box contents:
 120                 unpack!(block = this.into(&Place::Local(result).deref(), block, value));
 121                 block.and(Rvalue::Use(Operand::Move(Place::Local(result))))
 122             }
 123             ExprKind::Cast { source } => {
 124                 let source = this.hir.mirror(source);
 125
 126                 let source = unpack!(block = this.as_operand(block, scope, source));
 127                 block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
 128             }
 129             ExprKind::Use { source } => {
 130                 let source = unpack!(block = this.as_operand(block, scope, source));
 131                 block.and(Rvalue::Use(source))
 132             }
 133             ExprKind::ReifyFnPointer { source } => {
 134                 let source = unpack!(block = this.as_operand(block, scope, source));
 135                 block.and(Rvalue::Cast(CastKind::ReifyFnPointer, source, expr.ty))
 136             }
 137             ExprKind::UnsafeFnPointer { source } => {
 138                 let source = unpack!(block = this.as_operand(block, scope, source));
 139                 block.and(Rvalue::Cast(CastKind::UnsafeFnPointer, source, expr.ty))
 140             }
 141             ExprKind::ClosureFnPointer { source } => {
 142                 let source = unpack!(block = this.as_operand(block, scope, source));
 143                 block.and(Rvalue::Cast(CastKind::ClosureFnPointer, source, expr.ty))
 144             }
 145             ExprKind::Unsize { source } => {
 146                 let source = unpack!(block = this.as_operand(block, scope, source));
 147                 block.and(Rvalue::Cast(CastKind::Unsize, source, expr.ty))
 148             }
 149             ExprKind::Array { fields } => {
 150                 // (*) We would (maybe) be closer to trans if we
 151                 // handled this and other aggregate cases via
 152                 // `into()`, not `as_rvalue` -- in that case, instead
 153                 // of generating
 154                 //
 155                 //     let tmp1 = ...1;
 156                 //     let tmp2 = ...2;
 157                 //     dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
 158                 //
 159                 // we could just generate
 160                 //
 161                 //     dest.f = ...1;
 162                 //     dest.g = ...2;
 163                 //
 164                 // The problem is that then we would need to:
 165                 //
 166                 // (a) have a more complex mechanism for handling
 167                 //     partial cleanup;
 168                 // (b) distinguish the case where the type `Foo` has a
 169                 //     destructor, in which case creating an instance
 170                 //     as a whole "arms" the destructor, and you can't
 171                 //     write individual fields; and,
 172                 // (c) handle the case where the type Foo has no
 173                 //     fields. We don't want `let x: ();` to compile
 174                 //     to the same MIR as `let x = ();`.
 175
 176                 // first process the set of fields
 177                 let el_ty = expr.ty.sequence_element_type(this.hir.tcx());
 178                 let fields: Vec<_> =
 179                     fields.into_iter()
 180                           .map(|f| unpack!(block = this.as_operand(block, scope, f)))
 181                           .collect();
 182
 183                 block.and(Rvalue::Aggregate(box AggregateKind::Array(el_ty), fields))
 184             }
 185             ExprKind::Tuple { fields } => { // see (*) above
 186                 // first process the set of fields
 187                 let fields: Vec<_> =
 188                     fields.into_iter()
 189                           .map(|f| unpack!(block = this.as_operand(block, scope, f)))
 190                           .collect();
 191
 192                 block.and(Rvalue::Aggregate(box AggregateKind::Tuple, fields))
 193             }
 194             ExprKind::Closure { closure_id, substs, upvars, interior } => { // see (*) above
 195                 let mut operands: Vec<_> =
 196                     upvars.into_iter()
 197                           .map(|upvar| unpack!(block = this.as_operand(block, scope, upvar)))
 198                           .collect();
 199                 let result = if let Some(interior) = interior {
 200                     // Add the state operand since it follows the upvars in the generator
 201                     // struct. See librustc_mir/transform/generator.rs for more details.
 202                     operands.push(Operand::Constant(box Constant {
 203                         span: expr_span,
 204                         ty: this.hir.tcx().types.u32,
 205                         literal: Literal::Value {
 206                             value: this.hir.tcx().mk_const(ty::Const {
 207                                 val: ConstVal::Value(Value::ByVal(PrimVal::Bytes(0))),
 208                                 ty: this.hir.tcx().types.u32
 209                             }),
 210                         },
 211                     }));
 212                     box AggregateKind::Generator(closure_id, substs, interior)
 213                 } else {
 214                     box AggregateKind::Closure(closure_id, substs)
 215                 };
 216                 block.and(Rvalue::Aggregate(result, operands))
 217             }
 218             ExprKind::Adt {
 219                 adt_def, variant_index, substs, fields, base
 220             } => { // see (*) above
 221                 let is_union = adt_def.is_union();
 222                 let active_field_index = if is_union { Some(fields[0].name.index()) } else { None };
 223
 224                 // first process the set of fields that were provided
 225                 // (evaluating them in order given by user)
 226                 let fields_map: FxHashMap<_, _> = fields.into_iter()
 227                     .map(|f| (f.name, unpack!(block = this.as_operand(block, scope, f.expr))))
 228                     .collect();
 229
 230                 let field_names = this.hir.all_fields(adt_def, variant_index);
 231
 232                 let fields = if let Some(FruInfo { base, field_types }) = base {
 233                     let base = unpack!(block = this.as_place(block, base));
 234
 235                     // MIR does not natively support FRU, so for each
 236                     // base-supplied field, generate an operand that
 237                     // reads it from the base.
 238                     field_names.into_iter()
 239                         .zip(field_types.into_iter())
 240                         .map(|(n, ty)| match fields_map.get(&n) {
 241                             Some(v) => v.clone(),
 242                             None => this.consume_by_copy_or_move(base.clone().field(n, ty))
 243                         })
 244                         .collect()
 245                 } else {
 246                     field_names.iter().filter_map(|n| fields_map.get(n).cloned()).collect()
 247                 };
 248
 249                 let adt =
 250                     box AggregateKind::Adt(adt_def, variant_index, substs, active_field_index);
 251                 block.and(Rvalue::Aggregate(adt, fields))
 252             }
 253             ExprKind::Assign { .. } |
 254             ExprKind::AssignOp { .. } => {
 255                 block = unpack!(this.stmt_expr(block, expr));
 256                 block.and(this.unit_rvalue())
 257             }
 258             ExprKind::Yield { value } => {
 259                 let value = unpack!(block = this.as_operand(block, scope, value));
 260                 let resume = this.cfg.start_new_block();
 261                 let cleanup = this.generator_drop_cleanup();
 262                 this.cfg.terminate(block, source_info, TerminatorKind::Yield {
 263                     value: value,
 264                     resume: resume,
 265                     drop: cleanup,
 266                 });
 267                 resume.and(this.unit_rvalue())
 268             }
 269             ExprKind::Literal { .. } |
 270             ExprKind::Block { .. } |
 271             ExprKind::Match { .. } |
 272             ExprKind::If { .. } |
 273             ExprKind::NeverToAny { .. } |
 274             ExprKind::Loop { .. } |
 275             ExprKind::LogicalOp { .. } |
 276             ExprKind::Call { .. } |
 277             ExprKind::Field { .. } |
 278             ExprKind::Deref { .. } |
 279             ExprKind::Index { .. } |
 280             ExprKind::VarRef { .. } |
 281             ExprKind::SelfRef |
 282             ExprKind::Break { .. } |
 283             ExprKind::Continue { .. } |
 284             ExprKind::Return { .. } |
 285             ExprKind::InlineAsm { .. } |
 286             ExprKind::StaticRef { .. } => {
 287                 // these do not have corresponding `Rvalue` variants,
 288                 // so make an operand and then return that
 289                 debug_assert!(match Category::of(&expr.kind) {
 290                     Some(Category::Rvalue(RvalueFunc::AsRvalue)) => false,
 291                     _ => true,
 292                 });
 293                 let operand = unpack!(block = this.as_operand(block, scope, expr));
 294                 block.and(Rvalue::Use(operand))
 295             }
 296         }
 297     }
 298
 299     pub fn build_binary_op(&mut self, mut block: BasicBlock,
 300                            op: BinOp, span: Span, ty: Ty<'tcx>,
 301                            lhs: Operand<'tcx>, rhs: Operand<'tcx>) -> BlockAnd<Rvalue<'tcx>> {
 302         let source_info = self.source_info(span);
 303         let bool_ty = self.hir.bool_ty();
 304         if self.hir.check_overflow() && op.is_checkable() && ty.is_integral() {
 305             let result_tup = self.hir.tcx().intern_tup(&[ty, bool_ty], false);
 306             let result_value = self.temp(result_tup, span);
 307
 308             self.cfg.push_assign(block, source_info,
 309                                  &result_value, Rvalue::CheckedBinaryOp(op,
 310                                                                         lhs,
 311                                                                         rhs));
 312             let val_fld = Field::new(0);
 313             let of_fld = Field::new(1);
 314
 315             let val = result_value.clone().field(val_fld, ty);
 316             let of = result_value.field(of_fld, bool_ty);
 317
 318             let err = ConstMathErr::Overflow(match op {
 319                 BinOp::Add => Op::Add,
 320                 BinOp::Sub => Op::Sub,
 321                 BinOp::Mul => Op::Mul,
 322                 BinOp::Shl => Op::Shl,
 323                 BinOp::Shr => Op::Shr,
 324                 _ => {
 325                     bug!("MIR build_binary_op: {:?} is not checkable", op)
 326                 }
 327             });
 328
 329             block = self.assert(block, Operand::Move(of), false,
 330                                 AssertMessage::Math(err), span);
 331
 332             block.and(Rvalue::Use(Operand::Move(val)))
 333         } else {
 334             if ty.is_integral() && (op == BinOp::Div || op == BinOp::Rem) {
 335                 // Checking division and remainder is more complex, since we 1. always check
 336                 // and 2. there are two possible failure cases, divide-by-zero and overflow.
 337
 338                 let (zero_err, overflow_err) = if op == BinOp::Div {
 339                     (ConstMathErr::DivisionByZero,
 340                      ConstMathErr::Overflow(Op::Div))
 341                 } else {
 342                     (ConstMathErr::RemainderByZero,
 343                      ConstMathErr::Overflow(Op::Rem))
 344                 };
 345
 346                 // Check for / 0
 347                 let is_zero = self.temp(bool_ty, span);
 348                 let zero = self.zero_literal(span, ty);
 349                 self.cfg.push_assign(block, source_info, &is_zero,
 350                                      Rvalue::BinaryOp(BinOp::Eq, rhs.to_copy(), zero));
 351
 352                 block = self.assert(block, Operand::Move(is_zero), false,
 353                                     AssertMessage::Math(zero_err), span);
 354
 355                 // We only need to check for the overflow in one case:
 356                 // MIN / -1, and only for signed values.
 357                 if ty.is_signed() {
 358                     let neg_1 = self.neg_1_literal(span, ty);
 359                     let min = self.minval_literal(span, ty);
 360
 361                     let is_neg_1 = self.temp(bool_ty, span);
 362                     let is_min   = self.temp(bool_ty, span);
 363                     let of       = self.temp(bool_ty, span);
 364
 365                     // this does (rhs == -1) & (lhs == MIN). It could short-circuit instead
 366
 367                     self.cfg.push_assign(block, source_info, &is_neg_1,
 368                                          Rvalue::BinaryOp(BinOp::Eq, rhs.to_copy(), neg_1));
 369                     self.cfg.push_assign(block, source_info, &is_min,
 370                                          Rvalue::BinaryOp(BinOp::Eq, lhs.to_copy(), min));
 371
 372                     let is_neg_1 = Operand::Move(is_neg_1);
 373                     let is_min = Operand::Move(is_min);
 374                     self.cfg.push_assign(block, source_info, &of,
 375                                          Rvalue::BinaryOp(BinOp::BitAnd, is_neg_1, is_min));
 376
 377                     block = self.assert(block, Operand::Move(of), false,
 378                                         AssertMessage::Math(overflow_err), span);
 379                 }
 380             }
 381
 382             block.and(Rvalue::BinaryOp(op, lhs, rhs))
 383         }
 384     }
 385
 386     // Helper to get a `-1` value of the appropriate type
 387     fn neg_1_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 388         let literal = match ty.sty {
 389             ty::TyInt(ity) => {
 390                 let val = match ity {
 391                     ast::IntTy::I8  => ConstInt::I8(-1),
 392                     ast::IntTy::I16 => ConstInt::I16(-1),
 393                     ast::IntTy::I32 => ConstInt::I32(-1),
 394                     ast::IntTy::I64 => ConstInt::I64(-1),
 395                     ast::IntTy::I128 => ConstInt::I128(-1),
 396                     ast::IntTy::Isize => {
 397                         let int_ty = self.hir.tcx().sess.target.isize_ty;
 398                         let val = ConstIsize::new(-1, int_ty).unwrap();
 399                         ConstInt::Isize(val)
 400                     }
 401                 };
 402
 403                 Literal::Value {
 404                     value: self.hir.tcx().mk_const(ty::Const {
 405                         val: ConstVal::Value(Value::ByVal(PrimVal::Bytes(val.to_u128_unchecked()))),
 406                         ty
 407                     })
 408                 }
 409             }
 410             _ => {
 411                 span_bug!(span, "Invalid type for neg_1_literal: `{:?}`", ty)
 412             }
 413         };
 414
 415         self.literal_operand(span, ty, literal)
 416     }
 417
 418     // Helper to get the minimum value of the appropriate type
 419     fn minval_literal(&mut self, span: Span, ty: Ty<'tcx>) -> Operand<'tcx> {
 420         let literal = match ty.sty {
 421             ty::TyInt(ity) => {
 422                 let val = match ity {
 423                     ast::IntTy::I8  => ConstInt::I8(i8::min_value()),
 424                     ast::IntTy::I16 => ConstInt::I16(i16::min_value()),
 425                     ast::IntTy::I32 => ConstInt::I32(i32::min_value()),
 426                     ast::IntTy::I64 => ConstInt::I64(i64::min_value()),
 427                     ast::IntTy::I128 => ConstInt::I128(i128::min_value()),
 428                     ast::IntTy::Isize => {
 429                         let int_ty = self.hir.tcx().sess.target.isize_ty;
 430                         let min = match int_ty {
 431                             ast::IntTy::I16 => std::i16::MIN as i64,
 432                             ast::IntTy::I32 => std::i32::MIN as i64,
 433                             ast::IntTy::I64 => std::i64::MIN,
 434                             _ => unreachable!()
 435                         };
 436                         let val = ConstIsize::new(min, int_ty).unwrap();
 437                         ConstInt::Isize(val)
 438                     }
 439                 };
 440
 441                 Literal::Value {
 442                     value: self.hir.tcx().mk_const(ty::Const {
 443                         val: ConstVal::Value(Value::ByVal(PrimVal::Bytes(
 444                             val.to_u128_unchecked()
 445                         ))),
 446                         ty
 447                     })
 448                 }
 449             }
 450             _ => {
 451                 span_bug!(span, "Invalid type for minval_literal: `{:?}`", ty)
 452             }
 453         };
 454
 455         self.literal_operand(span, ty, literal)
 456     }
 457 }