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_middle::mir;
   6 use rustc_middle::mir::interpret::{InterpResult, Scalar};
   7 use rustc_target::abi::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_middle::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_middle::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: 'mir, 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     ///
  42     /// This is marked `#inline(always)` to work around adverserial codegen when `opt-level = 3`
  43     #[inline(always)]
  44     pub fn step(&mut self) -> InterpResult<'tcx, bool> {
  45         if self.stack().is_empty() {
  46             return Ok(false);
  47         }
  48
  49         let block = match self.frame().block {
  50             Some(block) => block,
  51             None => {
  52                 // We are unwinding and this fn has no cleanup code.
  53                 // Just go on unwinding.
  54                 trace!("unwinding: skipping frame");
  55                 self.pop_stack_frame(/* unwinding */ true)?;
  56                 return Ok(true);
  57             }
  58         };
  59         let stmt_id = self.frame().stmt;
  60         let body = self.body();
  61         let basic_block = &body.basic_blocks()[block];
  62
  63         let old_frames = self.frame_idx();
  64
  65         if let Some(stmt) = basic_block.statements.get(stmt_id) {
  66             assert_eq!(old_frames, self.frame_idx());
  67             self.statement(stmt)?;
  68             return Ok(true);
  69         }
  70
  71         M::before_terminator(self)?;
  72
  73         let terminator = basic_block.terminator();
  74         assert_eq!(old_frames, self.frame_idx());
  75         self.terminator(terminator)?;
  76         Ok(true)
  77     }
  78
  79     fn statement(&mut self, stmt: &mir::Statement<'tcx>) -> InterpResult<'tcx> {
  80         info!("{:?}", stmt);
  81         self.set_span(stmt.source_info.span);
  82
  83         use rustc_middle::mir::StatementKind::*;
  84
  85         // Some statements (e.g., box) push new stack frames.
  86         // We have to record the stack frame number *before* executing the statement.
  87         let frame_idx = self.frame_idx();
  88
  89         match &stmt.kind {
  90             Assign(box (place, rvalue)) => self.eval_rvalue_into_place(rvalue, *place)?,
  91
  92             SetDiscriminant { place, variant_index } => {
  93                 let dest = self.eval_place(**place)?;
  94                 self.write_discriminant_index(*variant_index, dest)?;
  95             }
  96
  97             // Mark locals as alive
  98             StorageLive(local) => {
  99                 let old_val = self.storage_live(*local)?;
 100                 self.deallocate_local(old_val)?;
 101             }
 102
 103             // Mark locals as dead
 104             StorageDead(local) => {
 105                 let old_val = self.storage_dead(*local);
 106                 self.deallocate_local(old_val)?;
 107             }
 108
 109             // No dynamic semantics attached to `FakeRead`; MIR
 110             // interpreter is solely intended for borrowck'ed code.
 111             FakeRead(..) => {}
 112
 113             // Stacked Borrows.
 114             Retag(kind, place) => {
 115                 let dest = self.eval_place(**place)?;
 116                 M::retag(self, *kind, dest)?;
 117             }
 118
 119             // Statements we do not track.
 120             AscribeUserType(..) => {}
 121
 122             // Defined to do nothing. These are added by optimization passes, to avoid changing the
 123             // size of MIR constantly.
 124             Nop => {}
 125
 126             LlvmInlineAsm { .. } => throw_unsup_format!("inline assembly is not supported"),
 127         }
 128
 129         self.stack_mut()[frame_idx].stmt += 1;
 130         Ok(())
 131     }
 132
 133     /// Evaluate an assignment statement.
 134     ///
 135     /// There is no separate `eval_rvalue` function. Instead, the code for handling each rvalue
 136     /// type writes its results directly into the memory specified by the place.
 137     pub fn eval_rvalue_into_place(
 138         &mut self,
 139         rvalue: &mir::Rvalue<'tcx>,
 140         place: mir::Place<'tcx>,
 141     ) -> InterpResult<'tcx> {
 142         let dest = self.eval_place(place)?;
 143
 144         use rustc_middle::mir::Rvalue::*;
 145         match *rvalue {
 146             Use(ref operand) => {
 147                 // Avoid recomputing the layout
 148                 let op = self.eval_operand(operand, Some(dest.layout))?;
 149                 self.copy_op(op, dest)?;
 150             }
 151
 152             BinaryOp(bin_op, ref left, ref right) => {
 153                 let layout = binop_left_homogeneous(bin_op).then_some(dest.layout);
 154                 let left = self.read_immediate(self.eval_operand(left, layout)?)?;
 155                 let layout = binop_right_homogeneous(bin_op).then_some(left.layout);
 156                 let right = self.read_immediate(self.eval_operand(right, layout)?)?;
 157                 self.binop_ignore_overflow(bin_op, left, right, dest)?;
 158             }
 159
 160             CheckedBinaryOp(bin_op, ref left, ref right) => {
 161                 // Due to the extra boolean in the result, we can never reuse the `dest.layout`.
 162                 let left = self.read_immediate(self.eval_operand(left, None)?)?;
 163                 let layout = binop_right_homogeneous(bin_op).then_some(left.layout);
 164                 let right = self.read_immediate(self.eval_operand(right, layout)?)?;
 165                 self.binop_with_overflow(bin_op, left, right, dest)?;
 166             }
 167
 168             UnaryOp(un_op, ref operand) => {
 169                 // The operand always has the same type as the result.
 170                 let val = self.read_immediate(self.eval_operand(operand, Some(dest.layout))?)?;
 171                 let val = self.unary_op(un_op, val)?;
 172                 assert_eq!(val.layout, dest.layout, "layout mismatch for result of {:?}", un_op);
 173                 self.write_immediate(*val, dest)?;
 174             }
 175
 176             Aggregate(ref kind, ref operands) => {
 177                 let (dest, active_field_index) = match **kind {
 178                     mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
 179                         self.write_discriminant_index(variant_index, dest)?;
 180                         if adt_def.is_enum() {
 181                             (self.place_downcast(dest, variant_index)?, active_field_index)
 182                         } else {
 183                             (dest, active_field_index)
 184                         }
 185                     }
 186                     _ => (dest, None),
 187                 };
 188
 189                 for (i, operand) in operands.iter().enumerate() {
 190                     let op = self.eval_operand(operand, None)?;
 191                     // Ignore zero-sized fields.
 192                     if !op.layout.is_zst() {
 193                         let field_index = active_field_index.unwrap_or(i);
 194                         let field_dest = self.place_field(dest, field_index)?;
 195                         self.copy_op(op, field_dest)?;
 196                     }
 197                 }
 198             }
 199
 200             Repeat(ref operand, _) => {
 201                 let op = self.eval_operand(operand, None)?;
 202                 let dest = self.force_allocation(dest)?;
 203                 let length = dest.len(self)?;
 204
 205                 if let Some(first_ptr) = self.check_mplace_access(dest, None)? {
 206                     // Write the first.
 207                     let first = self.mplace_field(dest, 0)?;
 208                     self.copy_op(op, first.into())?;
 209
 210                     if length > 1 {
 211                         let elem_size = first.layout.size;
 212                         // Copy the rest. This is performance-sensitive code
 213                         // for big static/const arrays!
 214                         let rest_ptr = first_ptr.offset(elem_size, self)?;
 215                         self.memory.copy_repeatedly(
 216                             first_ptr,
 217                             rest_ptr,
 218                             elem_size,
 219                             length - 1,
 220                             /*nonoverlapping:*/ true,
 221                         )?;
 222                     }
 223                 }
 224             }
 225
 226             Len(place) => {
 227                 // FIXME(CTFE): don't allow computing the length of arrays in const eval
 228                 let src = self.eval_place(place)?;
 229                 let mplace = self.force_allocation(src)?;
 230                 let len = mplace.len(self)?;
 231                 self.write_scalar(Scalar::from_machine_usize(len, self), dest)?;
 232             }
 233
 234             AddressOf(_, place) | Ref(_, _, place) => {
 235                 let src = self.eval_place(place)?;
 236                 let place = self.force_allocation(src)?;
 237                 if place.layout.size.bytes() > 0 {
 238                     // definitely not a ZST
 239                     assert!(place.ptr.is_ptr(), "non-ZST places should be normalized to `Pointer`");
 240                 }
 241                 self.write_immediate(place.to_ref(), dest)?;
 242             }
 243
 244             NullaryOp(mir::NullOp::Box, _) => {
 245                 M::box_alloc(self, dest)?;
 246             }
 247
 248             NullaryOp(mir::NullOp::SizeOf, ty) => {
 249                 let ty = self.subst_from_current_frame_and_normalize_erasing_regions(ty);
 250                 let layout = self.layout_of(ty)?;
 251                 assert!(
 252                     !layout.is_unsized(),
 253                     "SizeOf nullary MIR operator called for unsized type"
 254                 );
 255                 self.write_scalar(Scalar::from_machine_usize(layout.size.bytes(), self), 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(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.set_span(terminator.source_info.span);
 279
 280         self.eval_terminator(terminator)?;
 281         if !self.stack().is_empty() {
 282             if let Some(block) = self.frame().block {
 283                 info!("// executing {:?}", block);
 284             }
 285         }
 286         Ok(())
 287     }
 288 }