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