1 //! This module contains the `InterpCx` methods for executing a single step of the interpreter.
3 //! The main entry point is the `step` method.
6 use rustc_middle::mir::interpret::{InterpResult, Scalar};
7 use rustc_middle::ty::layout::LayoutOf;
9 use super::{InterpCx, Machine};
11 /// Classify whether an operator is "left-homogeneous", i.e., the LHS has the
12 /// same type as the result.
14 fn binop_left_homogeneous(op: mir::BinOp) -> bool {
15 use rustc_middle::mir::BinOp::*;
17 Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr | Offset | Shl | Shr => true,
18 Eq | Ne | Lt | Le | Gt | Ge => false,
21 /// Classify whether an operator is "right-homogeneous", i.e., the RHS has the
22 /// same type as the LHS.
24 fn binop_right_homogeneous(op: mir::BinOp) -> bool {
25 use rustc_middle::mir::BinOp::*;
27 Add | Sub | Mul | Div | Rem | BitXor | BitAnd | BitOr | Eq | Ne | Lt | Le | Gt | Ge => true,
28 Offset | Shl | Shr => false,
32 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
33 pub fn run(&mut self) -> InterpResult<'tcx> {
38 /// Returns `true` as long as there are more things to do.
40 /// This is used by [priroda](https://github.com/oli-obk/priroda)
42 /// This is marked `#inline(always)` to work around adversarial codegen when `opt-level = 3`
44 pub fn step(&mut self) -> InterpResult<'tcx, bool> {
45 if self.stack().is_empty() {
49 let Ok(loc) = self.frame().loc else {
50 // We are unwinding and this fn has no cleanup code.
51 // Just go on unwinding.
52 trace!("unwinding: skipping frame");
53 self.pop_stack_frame(/* unwinding */ true)?;
56 let basic_block = &self.body().basic_blocks[loc.block];
58 if let Some(stmt) = basic_block.statements.get(loc.statement_index) {
59 let old_frames = self.frame_idx();
60 self.statement(stmt)?;
61 // Make sure we are not updating `statement_index` of the wrong frame.
62 assert_eq!(old_frames, self.frame_idx());
63 // Advance the program counter.
64 self.frame_mut().loc.as_mut().unwrap().statement_index += 1;
68 M::before_terminator(self)?;
70 let terminator = basic_block.terminator();
71 self.terminator(terminator)?;
75 /// Runs the interpretation logic for the given `mir::Statement` at the current frame and
76 /// statement counter.
78 /// This does NOT move the statement counter forward, the caller has to do that!
79 pub fn statement(&mut self, stmt: &mir::Statement<'tcx>) -> InterpResult<'tcx> {
82 use rustc_middle::mir::StatementKind::*;
85 Assign(box (place, rvalue)) => self.eval_rvalue_into_place(rvalue, *place)?,
87 SetDiscriminant { place, variant_index } => {
88 let dest = self.eval_place(**place)?;
89 self.write_discriminant(*variant_index, &dest)?;
93 let dest = self.eval_place(**place)?;
94 self.write_uninit(&dest)?;
97 // Mark locals as alive
98 StorageLive(local) => {
99 self.storage_live(*local)?;
102 // Mark locals as dead
103 StorageDead(local) => {
104 self.storage_dead(*local)?;
107 // No dynamic semantics attached to `FakeRead`; MIR
108 // interpreter is solely intended for borrowck'ed code.
112 Retag(kind, place) => {
113 let dest = self.eval_place(**place)?;
114 M::retag(self, *kind, &dest)?;
117 Intrinsic(box ref intrinsic) => self.emulate_nondiverging_intrinsic(intrinsic)?,
119 // Statements we do not track.
120 AscribeUserType(..) => {}
122 // Currently, Miri discards Coverage statements. Coverage statements are only injected
123 // via an optional compile time MIR pass and have no side effects. Since Coverage
124 // statements don't exist at the source level, it is safe for Miri to ignore them, even
125 // for undefined behavior (UB) checks.
127 // A coverage counter inside a const expression (for example, a counter injected in a
128 // const function) is discarded when the const is evaluated at compile time. Whether
129 // this should change, and/or how to implement a const eval counter, is a subject of the
132 // FIXME(#73156): Handle source code coverage in const eval
135 // Defined to do nothing. These are added by optimization passes, to avoid changing the
136 // size of MIR constantly.
143 /// Evaluate an assignment statement.
145 /// There is no separate `eval_rvalue` function. Instead, the code for handling each rvalue
146 /// type writes its results directly into the memory specified by the place.
147 pub fn eval_rvalue_into_place(
149 rvalue: &mir::Rvalue<'tcx>,
150 place: mir::Place<'tcx>,
151 ) -> InterpResult<'tcx> {
152 let dest = self.eval_place(place)?;
153 // FIXME: ensure some kind of non-aliasing between LHS and RHS?
154 // Also see https://github.com/rust-lang/rust/issues/68364.
156 use rustc_middle::mir::Rvalue::*;
158 ThreadLocalRef(did) => {
159 let ptr = M::thread_local_static_base_pointer(self, did)?;
160 self.write_pointer(ptr, &dest)?;
163 Use(ref operand) => {
164 // Avoid recomputing the layout
165 let op = self.eval_operand(operand, Some(dest.layout))?;
166 self.copy_op(&op, &dest, /*allow_transmute*/ false)?;
169 CopyForDeref(ref place) => {
170 let op = self.eval_place_to_op(*place, Some(dest.layout))?;
171 self.copy_op(&op, &dest, /* allow_transmute*/ false)?;
174 BinaryOp(bin_op, box (ref left, ref right)) => {
175 let layout = binop_left_homogeneous(bin_op).then_some(dest.layout);
176 let left = self.read_immediate(&self.eval_operand(left, layout)?)?;
177 let layout = binop_right_homogeneous(bin_op).then_some(left.layout);
178 let right = self.read_immediate(&self.eval_operand(right, layout)?)?;
179 self.binop_ignore_overflow(bin_op, &left, &right, &dest)?;
182 CheckedBinaryOp(bin_op, box (ref left, ref right)) => {
183 // Due to the extra boolean in the result, we can never reuse the `dest.layout`.
184 let left = self.read_immediate(&self.eval_operand(left, None)?)?;
185 let layout = binop_right_homogeneous(bin_op).then_some(left.layout);
186 let right = self.read_immediate(&self.eval_operand(right, layout)?)?;
187 self.binop_with_overflow(
188 bin_op, /*force_overflow_checks*/ false, &left, &right, &dest,
192 UnaryOp(un_op, ref operand) => {
193 // The operand always has the same type as the result.
194 let val = self.read_immediate(&self.eval_operand(operand, Some(dest.layout))?)?;
195 let val = self.unary_op(un_op, &val)?;
196 assert_eq!(val.layout, dest.layout, "layout mismatch for result of {:?}", un_op);
197 self.write_immediate(*val, &dest)?;
200 Aggregate(box ref kind, ref operands) => {
201 assert!(matches!(kind, mir::AggregateKind::Array(..)));
203 for (field_index, operand) in operands.iter().enumerate() {
204 let op = self.eval_operand(operand, None)?;
205 let field_dest = self.place_field(&dest, field_index)?;
206 self.copy_op(&op, &field_dest, /*allow_transmute*/ false)?;
210 Repeat(ref operand, _) => {
211 let src = self.eval_operand(operand, None)?;
212 assert!(!src.layout.is_unsized());
213 let dest = self.force_allocation(&dest)?;
214 let length = dest.len(self)?;
217 // Nothing to copy... but let's still make sure that `dest` as a place is valid.
218 self.get_place_alloc_mut(&dest)?;
220 // Write the src to the first element.
221 let first = self.mplace_field(&dest, 0)?;
222 self.copy_op(&src, &first.into(), /*allow_transmute*/ false)?;
224 // This is performance-sensitive code for big static/const arrays! So we
225 // avoid writing each operand individually and instead just make many copies
226 // of the first element.
227 let elem_size = first.layout.size;
228 let first_ptr = first.ptr;
229 let rest_ptr = first_ptr.offset(elem_size, self)?;
230 // For the alignment of `rest_ptr`, we crucially do *not* use `first.align` as
231 // that place might be more aligned than its type mandates (a `u8` array could
232 // be 4-aligned if it sits at the right spot in a struct). Instead we use
233 // `first.layout.align`, i.e., the alignment given by the type.
234 self.mem_copy_repeatedly(
238 first.layout.align.abi,
241 /*nonoverlapping:*/ true,
247 let src = self.eval_place(place)?;
248 let op = self.place_to_op(&src)?;
249 let len = op.len(self)?;
250 self.write_scalar(Scalar::from_machine_usize(len, self), &dest)?;
253 AddressOf(_, place) | Ref(_, _, place) => {
254 let src = self.eval_place(place)?;
255 let place = self.force_allocation(&src)?;
256 self.write_immediate(place.to_ref(self), &dest)?;
259 NullaryOp(null_op, ty) => {
260 let ty = self.subst_from_current_frame_and_normalize_erasing_regions(ty)?;
261 let layout = self.layout_of(ty)?;
262 if layout.is_unsized() {
263 // FIXME: This should be a span_bug (#80742)
264 self.tcx.sess.delay_span_bug(
265 self.frame().current_span(),
266 &format!("Nullary MIR operator called for unsized type {}", ty),
268 throw_inval!(SizeOfUnsizedType(ty));
270 let val = match null_op {
271 mir::NullOp::SizeOf => layout.size.bytes(),
272 mir::NullOp::AlignOf => layout.align.abi.bytes(),
274 self.write_scalar(Scalar::from_machine_usize(val, self), &dest)?;
277 ShallowInitBox(ref operand, _) => {
278 let src = self.eval_operand(operand, None)?;
279 let v = self.read_immediate(&src)?;
280 self.write_immediate(*v, &dest)?;
283 Cast(cast_kind, ref operand, cast_ty) => {
284 let src = self.eval_operand(operand, None)?;
286 self.subst_from_current_frame_and_normalize_erasing_regions(cast_ty)?;
287 self.cast(&src, cast_kind, cast_ty, &dest)?;
290 Discriminant(place) => {
291 let op = self.eval_place_to_op(place, None)?;
292 let discr_val = self.read_discriminant(&op)?.0;
293 self.write_scalar(discr_val, &dest)?;
297 trace!("{:?}", self.dump_place(*dest));
302 /// Evaluate the given terminator. Will also adjust the stack frame and statement position accordingly.
303 fn terminator(&mut self, terminator: &mir::Terminator<'tcx>) -> InterpResult<'tcx> {
304 info!("{:?}", terminator.kind);
306 self.eval_terminator(terminator)?;
307 if !self.stack().is_empty() {
308 if let Ok(loc) = self.frame().loc {
309 info!("// executing {:?}", loc.block);