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