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;
  26 use rustc::mir::*;
  27 use syntax::ast;
  28 use syntax_pos::Span;
  29
  30 impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
  31     /// See comment on `as_local_operand`
  32     pub fn as_local_rvalue<M>(&mut self, block: BasicBlock, expr: M)
  33                              -> BlockAnd<Rvalue<'tcx>>
  34         where M: Mirror<'tcx, Output = Expr<'tcx>>
  35     {
  36         let local_scope = self.local_scope();
  37         self.as_rvalue(block, local_scope, expr)
  38     }
  39
  40     /// Compile `expr`, yielding an rvalue.
  41     pub fn as_rvalue<M>(&mut self, block: BasicBlock, scope: Option<region::Scope>, expr: M)
  42                         -> BlockAnd<Rvalue<'tcx>>
  43         where M: Mirror<'tcx, Output = Expr<'tcx>>
  44     {
  45         let expr = self.hir.mirror(expr);
  46         self.expr_as_rvalue(block, scope, expr)
  47     }
  48
  49     fn expr_as_rvalue(&mut self,
  50                       mut block: BasicBlock,
  51                       scope: Option<region::Scope>,
  52                       expr: Expr<'tcx>)
  53                       -> BlockAnd<Rvalue<'tcx>> {
  54         debug!("expr_as_rvalue(block={:?}, scope={:?}, expr={:?})", block, scope, expr);
  55
  56         let this = self;
  57         let expr_span = expr.span;
  58         let source_info = this.source_info(expr_span);
  59
  60         match expr.kind {
  61             ExprKind::Scope { region_scope, value } => {
  62                 let region_scope = (region_scope, source_info);
  63                 this.in_scope(region_scope, block, |this| this.as_rvalue(block, scope, value))
  64             }
  65             ExprKind::Repeat { value, count } => {
  66                 let value_operand = unpack!(block = this.as_operand(block, scope, value));
  67                 block.and(Rvalue::Repeat(value_operand, count))
  68             }
  69             ExprKind::Borrow { region, borrow_kind, arg } => {
  70                 let arg_lvalue = unpack!(block = this.as_lvalue(block, arg));
  71                 block.and(Rvalue::Ref(region, borrow_kind, arg_lvalue))
  72             }
  73             ExprKind::Binary { op, lhs, rhs } => {
  74                 let lhs = unpack!(block = this.as_operand(block, scope, lhs));
  75                 let rhs = unpack!(block = this.as_operand(block, scope, rhs));
  76                 this.build_binary_op(block, op, expr_span, expr.ty,
  77                                      lhs, rhs)
  78             }
  79             ExprKind::Unary { op, arg } => {
  80                 let arg = unpack!(block = this.as_operand(block, scope, arg));
  81                 // Check for -MIN on signed integers
  82                 if this.hir.check_overflow() && op == UnOp::Neg && expr.ty.is_signed() {
  83                     let bool_ty = this.hir.bool_ty();
  84
  85                     let minval = this.minval_literal(expr_span, expr.ty);
  86                     let is_min = this.temp(bool_ty, expr_span);
  87
  88                     this.cfg.push_assign(block, source_info, &is_min,
  89                                          Rvalue::BinaryOp(BinOp::Eq, arg.clone(), minval));
  90
  91                     let err = ConstMathErr::Overflow(Op::Neg);
  92                     block = this.assert(block, Operand::Consume(is_min), false,
  93                                         AssertMessage::Math(err), expr_span);
  94                 }
  95                 block.and(Rvalue::UnaryOp(op, arg))
  96             }
  97             ExprKind::Box { value } => {
  98                 let value = this.hir.mirror(value);
  99                 let result = this.local_decls.push(LocalDecl::new_temp(expr.ty, expr_span));
 100                 this.cfg.push(block, Statement {
 101                     source_info,
 102                     kind: StatementKind::StorageLive(result)
 103                 });
 104                 if let Some(scope) = scope {
 105                     // schedule a shallow free of that memory, lest we unwind:
 106                     this.schedule_drop(expr_span, scope, &Lvalue::Local(result), value.ty);
 107                 }
 108
 109                 // malloc some memory of suitable type (thus far, uninitialized):
 110                 let box_ = Rvalue::NullaryOp(NullOp::Box, value.ty);
 111                 this.cfg.push_assign(block, source_info, &Lvalue::Local(result), box_);
 112
 113                 // initialize the box contents:
 114                 unpack!(block = this.into(&Lvalue::Local(result).deref(), block, value));
 115                 block.and(Rvalue::Use(Operand::Consume(Lvalue::Local(result))))
 116             }
 117             ExprKind::Cast { source } => {
 118                 let source = this.hir.mirror(source);
 119
 120                 let source = unpack!(block = this.as_operand(block, scope, source));
 121                 block.and(Rvalue::Cast(CastKind::Misc, source, expr.ty))
 122             }
 123             ExprKind::Use { source } => {
 124                 let source = unpack!(block = this.as_operand(block, scope, source));
 125                 block.and(Rvalue::Use(source))
 126             }
 127             ExprKind::ReifyFnPointer { source } => {
 128                 let source = unpack!(block = this.as_operand(block, scope, source));
 129                 block.and(Rvalue::Cast(CastKind::ReifyFnPointer, source, expr.ty))
 130             }
 131             ExprKind::UnsafeFnPointer { source } => {
 132                 let source = unpack!(block = this.as_operand(block, scope, source));
 133                 block.and(Rvalue::Cast(CastKind::UnsafeFnPointer, source, expr.ty))
 134             }
 135             ExprKind::ClosureFnPointer { source } => {
 136                 let source = unpack!(block = this.as_operand(block, scope, source));
 137                 block.and(Rvalue::Cast(CastKind::ClosureFnPointer, source, expr.ty))
 138             }
 139             ExprKind::Unsize { source } => {
 140                 let source = unpack!(block = this.as_operand(block, scope, source));
 141                 block.and(Rvalue::Cast(CastKind::Unsize, source, expr.ty))
 142             }
 143             ExprKind::Array { fields } => {
 144                 // (*) We would (maybe) be closer to trans if we
 145                 // handled this and other aggregate cases via
 146                 // `into()`, not `as_rvalue` -- in that case, instead
 147                 // of generating
 148                 //
 149                 //     let tmp1 = ...1;
 150                 //     let tmp2 = ...2;
 151                 //     dest = Rvalue::Aggregate(Foo, [tmp1, tmp2])
 152                 //
 153                 // we could just generate
 154                 //
 155                 //     dest.f = ...1;
 156                 //     dest.g = ...2;
 157                 //
 158                 // The problem is that then we would need to:
 159                 //
 160                 // (a) have a more complex mechanism for handling
 161                 //     partial cleanup;
 162                 // (b) distinguish the case where the type `Foo` has a
 163                 //     destructor, in which case creating an instance
 164                 //     as a whole "arms" the destructor, and you can't
 165                 //     write individual fields; and,
 166                 // (c) handle the case where the type Foo has no
 167                 //     fields. We don't want `let x: ();` to compile
 168                 //     to the same MIR as `let x = ();`.
 169
 170                 // first process the set of fields
 171                 let el_ty = expr.ty.sequence_element_type(this.hir.tcx());
 172                 let fields: Vec<_> =
 173                     fields.into_iter()
 174                           .map(|f| unpack!(block = this.as_operand(block, scope, f)))
 175                           .collect();
 176
 177                 block.and(Rvalue::Aggregate(box AggregateKind::Array(el_ty), fields))
 178             }
 179             ExprKind::Tuple { fields } => { // see (*) above
 180                 // first process the set of fields
 181                 let fields: Vec<_> =
 182                     fields.into_iter()
 183                           .map(|f| unpack!(block = this.as_operand(block, scope, f)))
 184                           .collect();
 185
 186                 block.and(Rvalue::Aggregate(box AggregateKind::Tuple, fields))
 187             }
 188             ExprKind::Closure { closure_id, substs, upvars, interior } => { // see (*) above
 189                 let mut operands: Vec<_> =
 190                     upvars.into_iter()
 191                           .map(|upvar| unpack!(block = this.as_operand(block, scope, upvar)))
 192                           .collect();
 193                 let result = if let Some(interior) = interior {
 194                     // Add the state operand since it follows the upvars in the generator
 195                     // struct. See librustc_mir/transform/generator.rs for more details.
 196                     operands.push(Operand::Constant(box Constant {
 197                         span: expr_span,
 198                         ty: this.hir.tcx().types.u32,
 199                         literal: Literal::Value {
 200                             value: this.hir.tcx().mk_const(ty::Const {
 201                                 val: ConstVal::Integral(ConstInt::U32(0)),
 202                                 ty: this.hir.tcx().types.u32
 203                             }),
 204                         },
 205                     }));
 206                     box AggregateKind::Generator(closure_id, substs, interior)
 207                 } else {
 208                     box AggregateKind::Closure(closure_id, substs)
 209                 };
 210                 block.and(Rvalue::Aggregate(result, operands))
 211             }
 212             ExprKind::Adt {
 213                 adt_def, variant_index, substs, fields, base
 214             } => { // see (*) above
 215                 let is_union = adt_def.is_union();
 216                 let active_field_index = if is_union { Some(fields[0].name.index()) } else { None };
 217
 218                 // first process the set of fields that were provided
 219                 // (evaluating them in order given by user)
 220                 let fields_map: FxHashMap<_, _> = fields.into_iter()
 221                     .map(|f| (f.name, unpack!(block = this.as_operand(block, scope, f.expr))))
 222                     .collect();
 223
 224                 let field_names = this.hir.all_fields(adt_def, variant_index);
 225
 226                 let fields = if let Some(FruInfo { base, field_types }) = base {
 227                     let base = unpack!(block = this.as_lvalue(block, base));
 228
 229                     // MIR does not natively support FRU, so for each
 230                     // base-supplied field, generate an operand that
 231                     // reads it from the base.
 232                     field_names.into_iter()
 233                         .zip(field_types.into_iter())
 234                         .map(|(n, ty)| match fields_map.get(&n) {
 235                             Some(v) => v.clone(),
 236                             None => Operand::Consume(base.clone().field(n, ty))
 237                         })
 238                         .collect()
 239                 } else {
 240                     field_names.iter().filter_map(|n| fields_map.get(n).cloned()).collect()
 241                 };
 242
 243                 let adt =
 244                     box AggregateKind::Adt(adt_def, variant_index, substs, active_field_index);
 245                 block.and(Rvalue::Aggregate(adt, fields))
 246             }
 247             ExprKind::Assign { .. } |
 248             ExprKind::AssignOp { .. } => {
 249                 block = unpack!(this.stmt_expr(block, expr));
 250                 block.and(this.unit_rvalue())
 251             }
 252             ExprKind::Yield { value } => {
 253                 let value = unpack!(block = this.as_operand(block, scope, value));
 254                 let resume = this.cfg.start_new_block();
 255                 let cleanup = this.generator_drop_cleanup();
 256                 this.cfg.terminate(block, source_info, TerminatorKind::Yield {
 257                     value: value,
 258                     resume: resume,
 259                     drop: cleanup,
 260                 });
 261                 resume.and(this.unit_rvalue())
 262             }
 263             ExprKind::Literal { .. } |
 264             ExprKind::Block { .. } |
 265             ExprKind::Match { .. } |
 266             ExprKind::If { .. } |
 267             ExprKind::NeverToAny { .. } |
 268             ExprKind::Loop { .. } |
 269             ExprKind::LogicalOp { .. } |
 270             ExprKind::Call { .. } |
 271             ExprKind::Field { .. } |
 272             ExprKind::Deref { .. } |
 273             ExprKind::Index { .. } |
 274             ExprKind::VarRef { .. } |
 275             ExprKind::SelfRef |
 276             ExprKind::Break { .. } |
 277             ExprKind::Continue { .. } |
 278             ExprKind::Return { .. } |
 279             ExprKind::InlineAsm { .. } |
 280             ExprKind::StaticRef { .. } => {
 281                 // these do not have corresponding `Rvalue` variants,
 282                 // so make an operand and then return that
 283                 debug_assert!(match Category::of(&expr.kind) {
 284                     Some(Category::Rvalue(RvalueFunc::AsRvalue)) => false,
 285                     _ => true,
 286                 });
 287                 let operand = unpack!(block = this.as_operand(block, scope, expr));
 288                 block.and(Rvalue::Use(operand))
 289             }
 290         }
 291     }
 292
 293     pub fn build_binary_op(&mut self, mut block: BasicBlock,
 294                            op: BinOp, span: Span, ty: ty::Ty<'tcx>,
 295                            lhs: Operand<'tcx>, rhs: Operand<'tcx>) -> BlockAnd<Rvalue<'tcx>> {
 296         let source_info = self.source_info(span);
 297         let bool_ty = self.hir.bool_ty();
 298         if self.hir.check_overflow() && op.is_checkable() && ty.is_integral() {
 299             let result_tup = self.hir.tcx().intern_tup(&[ty, bool_ty], false);
 300             let result_value = self.temp(result_tup, span);
 301
 302             self.cfg.push_assign(block, source_info,
 303                                  &result_value, Rvalue::CheckedBinaryOp(op,
 304                                                                         lhs,
 305                                                                         rhs));
 306             let val_fld = Field::new(0);
 307             let of_fld = Field::new(1);
 308
 309             let val = result_value.clone().field(val_fld, ty);
 310             let of = result_value.field(of_fld, bool_ty);
 311
 312             let err = ConstMathErr::Overflow(match op {
 313                 BinOp::Add => Op::Add,
 314                 BinOp::Sub => Op::Sub,
 315                 BinOp::Mul => Op::Mul,
 316                 BinOp::Shl => Op::Shl,
 317                 BinOp::Shr => Op::Shr,
 318                 _ => {
 319                     bug!("MIR build_binary_op: {:?} is not checkable", op)
 320                 }
 321             });
 322
 323             block = self.assert(block, Operand::Consume(of), false,
 324                                 AssertMessage::Math(err), span);
 325
 326             block.and(Rvalue::Use(Operand::Consume(val)))
 327         } else {
 328             if ty.is_integral() && (op == BinOp::Div || op == BinOp::Rem) {
 329                 // Checking division and remainder is more complex, since we 1. always check
 330                 // and 2. there are two possible failure cases, divide-by-zero and overflow.
 331
 332                 let (zero_err, overflow_err) = if op == BinOp::Div {
 333                     (ConstMathErr::DivisionByZero,
 334                      ConstMathErr::Overflow(Op::Div))
 335                 } else {
 336                     (ConstMathErr::RemainderByZero,
 337                      ConstMathErr::Overflow(Op::Rem))
 338                 };
 339
 340                 // Check for / 0
 341                 let is_zero = self.temp(bool_ty, span);
 342                 let zero = self.zero_literal(span, ty);
 343                 self.cfg.push_assign(block, source_info, &is_zero,
 344                                      Rvalue::BinaryOp(BinOp::Eq, rhs.clone(), zero));
 345
 346                 block = self.assert(block, Operand::Consume(is_zero), false,
 347                                     AssertMessage::Math(zero_err), span);
 348
 349                 // We only need to check for the overflow in one case:
 350                 // MIN / -1, and only for signed values.
 351                 if ty.is_signed() {
 352                     let neg_1 = self.neg_1_literal(span, ty);
 353                     let min = self.minval_literal(span, ty);
 354
 355                     let is_neg_1 = self.temp(bool_ty, span);
 356                     let is_min   = self.temp(bool_ty, span);
 357                     let of       = self.temp(bool_ty, span);
 358
 359                     // this does (rhs == -1) & (lhs == MIN). It could short-circuit instead
 360
 361                     self.cfg.push_assign(block, source_info, &is_neg_1,
 362                                          Rvalue::BinaryOp(BinOp::Eq, rhs.clone(), neg_1));
 363                     self.cfg.push_assign(block, source_info, &is_min,
 364                                          Rvalue::BinaryOp(BinOp::Eq, lhs.clone(), min));
 365
 366                     let is_neg_1 = Operand::Consume(is_neg_1);
 367                     let is_min = Operand::Consume(is_min);
 368                     self.cfg.push_assign(block, source_info, &of,
 369                                          Rvalue::BinaryOp(BinOp::BitAnd, is_neg_1, is_min));
 370
 371                     block = self.assert(block, Operand::Consume(of), false,
 372                                         AssertMessage::Math(overflow_err), span);
 373                 }
 374             }
 375
 376             block.and(Rvalue::BinaryOp(op, lhs, rhs))
 377         }
 378     }
 379
 380     // Helper to get a `-1` value of the appropriate type
 381     fn neg_1_literal(&mut self, span: Span, ty: ty::Ty<'tcx>) -> Operand<'tcx> {
 382         let literal = match ty.sty {
 383             ty::TyInt(ity) => {
 384                 let val = match ity {
 385                     ast::IntTy::I8  => ConstInt::I8(-1),
 386                     ast::IntTy::I16 => ConstInt::I16(-1),
 387                     ast::IntTy::I32 => ConstInt::I32(-1),
 388                     ast::IntTy::I64 => ConstInt::I64(-1),
 389                     ast::IntTy::I128 => ConstInt::I128(-1),
 390                     ast::IntTy::Is => {
 391                         let int_ty = self.hir.tcx().sess.target.isize_ty;
 392                         let val = ConstIsize::new(-1, int_ty).unwrap();
 393                         ConstInt::Isize(val)
 394                     }
 395                 };
 396
 397                 Literal::Value {
 398                     value: self.hir.tcx().mk_const(ty::Const {
 399                         val: ConstVal::Integral(val),
 400                         ty
 401                     })
 402                 }
 403             }
 404             _ => {
 405                 span_bug!(span, "Invalid type for neg_1_literal: `{:?}`", ty)
 406             }
 407         };
 408
 409         self.literal_operand(span, ty, literal)
 410     }
 411
 412     // Helper to get the minimum value of the appropriate type
 413     fn minval_literal(&mut self, span: Span, ty: ty::Ty<'tcx>) -> Operand<'tcx> {
 414         let literal = match ty.sty {
 415             ty::TyInt(ity) => {
 416                 let val = match ity {
 417                     ast::IntTy::I8  => ConstInt::I8(i8::min_value()),
 418                     ast::IntTy::I16 => ConstInt::I16(i16::min_value()),
 419                     ast::IntTy::I32 => ConstInt::I32(i32::min_value()),
 420                     ast::IntTy::I64 => ConstInt::I64(i64::min_value()),
 421                     ast::IntTy::I128 => ConstInt::I128(i128::min_value()),
 422                     ast::IntTy::Is => {
 423                         let int_ty = self.hir.tcx().sess.target.isize_ty;
 424                         let min = match int_ty {
 425                             ast::IntTy::I16 => std::i16::MIN as i64,
 426                             ast::IntTy::I32 => std::i32::MIN as i64,
 427                             ast::IntTy::I64 => std::i64::MIN,
 428                             _ => unreachable!()
 429                         };
 430                         let val = ConstIsize::new(min, int_ty).unwrap();
 431                         ConstInt::Isize(val)
 432                     }
 433                 };
 434
 435                 Literal::Value {
 436                     value: self.hir.tcx().mk_const(ty::Const {
 437                         val: ConstVal::Integral(val),
 438                         ty
 439                     })
 440                 }
 441             }
 442             _ => {
 443                 span_bug!(span, "Invalid type for minval_literal: `{:?}`", ty)
 444             }
 445         };
 446
 447         self.literal_operand(span, ty, literal)
 448     }
 449 }