src/librustc_mir/interpret/step.rs

   1 //! This module contains the `InterpCx` methods for executing a single step of the interpreter.
   2 //!
   3 //! The main entry point is the `step` method.
   4
   5 use rustc::mir;
   6 use rustc::mir::interpret::{InterpResult, PointerArithmetic, Scalar};
   7 use rustc::ty::layout::LayoutOf;
   8
   9 use super::{InterpCx, Machine};
  10
  11 /// Classify whether an operator is "left-homogeneous", i.e., the LHS has the
  12 /// same type as the result.
  13 #[inline]
  14 fn binop_left_homogeneous(op: mir::BinOp) -> bool {
  15     use rustc::mir::BinOp::*;
  16     match op {
  17         Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr | Offset | Shl | Shr => true,
  18         Eq | Ne | Lt | Le | Gt | Ge => false,
  19     }
  20 }
  21 /// Classify whether an operator is "right-homogeneous", i.e., the RHS has the
  22 /// same type as the LHS.
  23 #[inline]
  24 fn binop_right_homogeneous(op: mir::BinOp) -> bool {
  25     use rustc::mir::BinOp::*;
  26     match op {
  27         Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr | Eq | Ne | Lt | Le | Gt | Ge => true,
  28         Offset | Shl | Shr => false,
  29     }
  30 }
  31
  32 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
  33     pub fn run(&mut self) -> InterpResult<'tcx> {
  34         while self.step()? {}
  35         Ok(())
  36     }
  37
  38     /// Returns `true` as long as there are more things to do.
  39     ///
  40     /// This is used by [priroda](https://github.com/oli-obk/priroda)
  41     pub fn step(&mut self) -> InterpResult<'tcx, bool> {
  42         if self.stack.is_empty() {
  43             return Ok(false);
  44         }
  45
  46         let block = match self.frame().block {
  47             Some(block) => block,
  48             None => {
  49                 // We are unwinding and this fn has no cleanup code.
  50                 // Just go on unwinding.
  51                 trace!("unwinding: skipping frame");
  52                 self.pop_stack_frame(/* unwinding */ true)?;
  53                 return Ok(true);
  54             }
  55         };
  56         let stmt_id = self.frame().stmt;
  57         let body = self.body();
  58         let basic_block = &body.basic_blocks()[block];
  59
  60         let old_frames = self.cur_frame();
  61
  62         if let Some(stmt) = basic_block.statements.get(stmt_id) {
  63             assert_eq!(old_frames, self.cur_frame());
  64             self.statement(stmt)?;
  65             return Ok(true);
  66         }
  67
  68         M::before_terminator(self)?;
  69
  70         let terminator = basic_block.terminator();
  71         assert_eq!(old_frames, self.cur_frame());
  72         self.terminator(terminator)?;
  73         Ok(true)
  74     }
  75
  76     fn statement(&mut self, stmt: &mir::Statement<'tcx>) -> InterpResult<'tcx> {
  77         info!("{:?}", stmt);
  78
  79         use rustc::mir::StatementKind::*;
  80
  81         // Some statements (e.g., box) push new stack frames.
  82         // We have to record the stack frame number *before* executing the statement.
  83         let frame_idx = self.cur_frame();
  84         self.tcx.span = stmt.source_info.span;
  85         self.memory.tcx.span = stmt.source_info.span;
  86
  87         match stmt.kind {
  88             Assign(box (ref place, ref rvalue)) => self.eval_rvalue_into_place(rvalue, place)?,
  89
  90             SetDiscriminant { ref place, variant_index } => {
  91                 let dest = self.eval_place(place)?;
  92                 self.write_discriminant_index(variant_index, dest)?;
  93             }
  94
  95             // Mark locals as alive
  96             StorageLive(local) => {
  97                 let old_val = self.storage_live(local)?;
  98                 self.deallocate_local(old_val)?;
  99             }
 100
 101             // Mark locals as dead
 102             StorageDead(local) => {
 103                 let old_val = self.storage_dead(local);
 104                 self.deallocate_local(old_val)?;
 105             }
 106
 107             // No dynamic semantics attached to `FakeRead`; MIR
 108             // interpreter is solely intended for borrowck'ed code.
 109             FakeRead(..) => {}
 110
 111             // Stacked Borrows.
 112             Retag(kind, ref place) => {
 113                 let dest = self.eval_place(place)?;
 114                 M::retag(self, kind, dest)?;
 115             }
 116
 117             // Statements we do not track.
 118             AscribeUserType(..) => {}
 119
 120             // Defined to do nothing. These are added by optimization passes, to avoid changing the
 121             // size of MIR constantly.
 122             Nop => {}
 123
 124             InlineAsm { .. } => throw_unsup_format!("inline assembly is not supported"),
 125         }
 126
 127         self.stack[frame_idx].stmt += 1;
 128         Ok(())
 129     }
 130
 131     /// Evaluate an assignment statement.
 132     ///
 133     /// There is no separate `eval_rvalue` function. Instead, the code for handling each rvalue
 134     /// type writes its results directly into the memory specified by the place.
 135     pub fn eval_rvalue_into_place(
 136         &mut self,
 137         rvalue: &mir::Rvalue<'tcx>,
 138         place: &mir::Place<'tcx>,
 139     ) -> InterpResult<'tcx> {
 140         let dest = self.eval_place(place)?;
 141
 142         use rustc::mir::Rvalue::*;
 143         match *rvalue {
 144             Use(ref operand) => {
 145                 // Avoid recomputing the layout
 146                 let op = self.eval_operand(operand, Some(dest.layout))?;
 147                 self.copy_op(op, dest)?;
 148             }
 149
 150             BinaryOp(bin_op, ref left, ref right) => {
 151                 let layout = binop_left_homogeneous(bin_op).then_some(dest.layout);
 152                 let left = self.read_immediate(self.eval_operand(left, layout)?)?;
 153                 let layout = binop_right_homogeneous(bin_op).then_some(left.layout);
 154                 let right = self.read_immediate(self.eval_operand(right, layout)?)?;
 155                 self.binop_ignore_overflow(bin_op, left, right, dest)?;
 156             }
 157
 158             CheckedBinaryOp(bin_op, ref left, ref right) => {
 159                 // Due to the extra boolean in the result, we can never reuse the `dest.layout`.
 160                 let left = self.read_immediate(self.eval_operand(left, None)?)?;
 161                 let layout = binop_right_homogeneous(bin_op).then_some(left.layout);
 162                 let right = self.read_immediate(self.eval_operand(right, layout)?)?;
 163                 self.binop_with_overflow(bin_op, left, right, dest)?;
 164             }
 165
 166             UnaryOp(un_op, ref operand) => {
 167                 // The operand always has the same type as the result.
 168                 let val = self.read_immediate(self.eval_operand(operand, Some(dest.layout))?)?;
 169                 let val = self.unary_op(un_op, val)?;
 170                 assert_eq!(val.layout, dest.layout, "layout mismatch for result of {:?}", un_op);
 171                 self.write_immediate(*val, dest)?;
 172             }
 173
 174             Aggregate(ref kind, ref operands) => {
 175                 let (dest, active_field_index) = match **kind {
 176                     mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
 177                         self.write_discriminant_index(variant_index, dest)?;
 178                         if adt_def.is_enum() {
 179                             (self.place_downcast(dest, variant_index)?, active_field_index)
 180                         } else {
 181                             (dest, active_field_index)
 182                         }
 183                     }
 184                     _ => (dest, None),
 185                 };
 186
 187                 for (i, operand) in operands.iter().enumerate() {
 188                     let op = self.eval_operand(operand, None)?;
 189                     // Ignore zero-sized fields.
 190                     if !op.layout.is_zst() {
 191                         let field_index = active_field_index.unwrap_or(i);
 192                         let field_dest = self.place_field(dest, field_index as u64)?;
 193                         self.copy_op(op, field_dest)?;
 194                     }
 195                 }
 196             }
 197
 198             Repeat(ref operand, _) => {
 199                 let op = self.eval_operand(operand, None)?;
 200                 let dest = self.force_allocation(dest)?;
 201                 let length = dest.len(self)?;
 202
 203                 if let Some(first_ptr) = self.check_mplace_access(dest, None)? {
 204                     // Write the first.
 205                     let first = self.mplace_field(dest, 0)?;
 206                     self.copy_op(op, first.into())?;
 207
 208                     if length > 1 {
 209                         let elem_size = first.layout.size;
 210                         // Copy the rest. This is performance-sensitive code
 211                         // for big static/const arrays!
 212                         let rest_ptr = first_ptr.offset(elem_size, self)?;
 213                         self.memory.copy_repeatedly(
 214                             first_ptr,
 215                             rest_ptr,
 216                             elem_size,
 217                             length - 1,
 218                             /*nonoverlapping:*/ true,
 219                         )?;
 220                     }
 221                 }
 222             }
 223
 224             Len(ref place) => {
 225                 // FIXME(CTFE): don't allow computing the length of arrays in const eval
 226                 let src = self.eval_place(place)?;
 227                 let mplace = self.force_allocation(src)?;
 228                 let len = mplace.len(self)?;
 229                 let size = self.pointer_size();
 230                 self.write_scalar(Scalar::from_uint(len, size), dest)?;
 231             }
 232
 233             AddressOf(_, ref place) | Ref(_, _, ref place) => {
 234                 let src = self.eval_place(place)?;
 235                 let place = self.force_allocation(src)?;
 236                 if place.layout.size.bytes() > 0 {
 237                     // definitely not a ZST
 238                     assert!(place.ptr.is_ptr(), "non-ZST places should be normalized to `Pointer`");
 239                 }
 240                 self.write_immediate(place.to_ref(), dest)?;
 241             }
 242
 243             NullaryOp(mir::NullOp::Box, _) => {
 244                 M::box_alloc(self, dest)?;
 245             }
 246
 247             NullaryOp(mir::NullOp::SizeOf, ty) => {
 248                 let ty = self.subst_from_frame_and_normalize_erasing_regions(ty);
 249                 let layout = self.layout_of(ty)?;
 250                 assert!(
 251                     !layout.is_unsized(),
 252                     "SizeOf nullary MIR operator called for unsized type"
 253                 );
 254                 let size = self.pointer_size();
 255                 self.write_scalar(Scalar::from_uint(layout.size.bytes(), size), dest)?;
 256             }
 257
 258             Cast(kind, ref operand, _) => {
 259                 let src = self.eval_operand(operand, None)?;
 260                 self.cast(src, kind, dest)?;
 261             }
 262
 263             Discriminant(ref place) => {
 264                 let op = self.eval_place_to_op(place, None)?;
 265                 let discr_val = self.read_discriminant(op)?.0;
 266                 let size = dest.layout.size;
 267                 self.write_scalar(Scalar::from_uint(discr_val, size), dest)?;
 268             }
 269         }
 270
 271         self.dump_place(*dest);
 272
 273         Ok(())
 274     }
 275
 276     fn terminator(&mut self, terminator: &mir::Terminator<'tcx>) -> InterpResult<'tcx> {
 277         info!("{:?}", terminator.kind);
 278         self.tcx.span = terminator.source_info.span;
 279         self.memory.tcx.span = terminator.source_info.span;
 280
 281         let old_stack = self.cur_frame();
 282         let old_bb = self.frame().block;
 283
 284         self.eval_terminator(terminator)?;
 285         if !self.stack.is_empty() {
 286             // This should change *something*
 287             debug_assert!(self.cur_frame() != old_stack || self.frame().block != old_bb);
 288             if let Some(block) = self.frame().block {
 289                 info!("// executing {:?}", block);
 290             }
 291         }
 292         Ok(())
 293     }
 294 }