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_target::abi::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 adverserial codegen when `opt-level = 3`
44 pub fn step(&mut self) -> InterpResult<'tcx, bool> {
45 if self.stack().is_empty() {
49 let loc = match self.frame().loc {
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)?;
59 let basic_block = &self.body().basic_blocks()[loc.block];
61 let old_frames = self.frame_idx();
63 if let Some(stmt) = basic_block.statements.get(loc.statement_index) {
64 assert_eq!(old_frames, self.frame_idx());
65 self.statement(stmt)?;
69 M::before_terminator(self)?;
71 let terminator = basic_block.terminator();
72 assert_eq!(old_frames, self.frame_idx());
73 self.terminator(terminator)?;
77 /// Runs the interpretation logic for the given `mir::Statement` at the current frame and
78 /// statement counter. This also moves the statement counter forward.
79 crate fn statement(&mut self, stmt: &mir::Statement<'tcx>) -> InterpResult<'tcx> {
82 use rustc_middle::mir::StatementKind::*;
84 // Some statements (e.g., box) push new stack frames.
85 // We have to record the stack frame number *before* executing the statement.
86 let frame_idx = self.frame_idx();
89 Assign(box (place, rvalue)) => self.eval_rvalue_into_place(rvalue, *place)?,
91 SetDiscriminant { place, variant_index } => {
92 let dest = self.eval_place(**place)?;
93 self.write_discriminant(*variant_index, &dest)?;
96 // Mark locals as alive
97 StorageLive(local) => {
98 self.storage_live(*local)?;
101 // Mark locals as dead
102 StorageDead(local) => {
103 self.storage_dead(*local)?;
106 // No dynamic semantics attached to `FakeRead`; MIR
107 // interpreter is solely intended for borrowck'ed code.
111 Retag(kind, place) => {
112 let dest = self.eval_place(**place)?;
113 M::retag(self, *kind, &dest)?;
116 // Statements we do not track.
117 AscribeUserType(..) => {}
119 // Currently, Miri discards Coverage statements. Coverage statements are only injected
120 // via an optional compile time MIR pass and have no side effects. Since Coverage
121 // statements don't exist at the source level, it is safe for Miri to ignore them, even
122 // for undefined behavior (UB) checks.
124 // A coverage counter inside a const expression (for example, a counter injected in a
125 // const function) is discarded when the const is evaluated at compile time. Whether
126 // this should change, and/or how to implement a const eval counter, is a subject of the
129 // FIXME(#73156): Handle source code coverage in const eval
132 // Defined to do nothing. These are added by optimization passes, to avoid changing the
133 // size of MIR constantly.
136 LlvmInlineAsm { .. } => throw_unsup_format!("inline assembly is not supported"),
139 self.stack_mut()[frame_idx].loc.as_mut().unwrap().statement_index += 1;
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)?;
154 use rustc_middle::mir::Rvalue::*;
156 ThreadLocalRef(did) => {
157 let id = M::thread_local_static_alloc_id(self, did)?;
158 let val = self.global_base_pointer(id.into())?;
159 self.write_scalar(val, &dest)?;
162 Use(ref operand) => {
163 // Avoid recomputing the layout
164 let op = self.eval_operand(operand, Some(dest.layout))?;
165 self.copy_op(&op, &dest)?;
168 BinaryOp(bin_op, box (ref left, ref right)) => {
169 let layout = binop_left_homogeneous(bin_op).then_some(dest.layout);
170 let left = self.read_immediate(&self.eval_operand(left, layout)?)?;
171 let layout = binop_right_homogeneous(bin_op).then_some(left.layout);
172 let right = self.read_immediate(&self.eval_operand(right, layout)?)?;
173 self.binop_ignore_overflow(bin_op, &left, &right, &dest)?;
176 CheckedBinaryOp(bin_op, box (ref left, ref right)) => {
177 // Due to the extra boolean in the result, we can never reuse the `dest.layout`.
178 let left = self.read_immediate(&self.eval_operand(left, None)?)?;
179 let layout = binop_right_homogeneous(bin_op).then_some(left.layout);
180 let right = self.read_immediate(&self.eval_operand(right, layout)?)?;
181 self.binop_with_overflow(bin_op, &left, &right, &dest)?;
184 UnaryOp(un_op, ref operand) => {
185 // The operand always has the same type as the result.
186 let val = self.read_immediate(&self.eval_operand(operand, Some(dest.layout))?)?;
187 let val = self.unary_op(un_op, &val)?;
188 assert_eq!(val.layout, dest.layout, "layout mismatch for result of {:?}", un_op);
189 self.write_immediate(*val, &dest)?;
192 Aggregate(ref kind, ref operands) => {
193 let (dest, active_field_index) = match **kind {
194 mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
195 self.write_discriminant(variant_index, &dest)?;
196 if adt_def.is_enum() {
197 (self.place_downcast(&dest, variant_index)?, active_field_index)
199 (dest, active_field_index)
205 for (i, operand) in operands.iter().enumerate() {
206 let op = self.eval_operand(operand, None)?;
207 // Ignore zero-sized fields.
208 if !op.layout.is_zst() {
209 let field_index = active_field_index.unwrap_or(i);
210 let field_dest = self.place_field(&dest, field_index)?;
211 self.copy_op(&op, &field_dest)?;
216 Repeat(ref operand, _) => {
217 let op = self.eval_operand(operand, None)?;
218 let dest = self.force_allocation(&dest)?;
219 let length = dest.len(self)?;
221 if let Some(first_ptr) = self.check_mplace_access(&dest, None)? {
223 let first = self.mplace_field(&dest, 0)?;
224 self.copy_op(&op, &first.into())?;
227 let elem_size = first.layout.size;
228 // Copy the rest. This is performance-sensitive code
229 // for big static/const arrays!
230 let rest_ptr = first_ptr.offset(elem_size, self)?;
231 self.memory.copy_repeatedly(
236 /*nonoverlapping:*/ true,
243 // FIXME(CTFE): don't allow computing the length of arrays in const eval
244 let src = self.eval_place(place)?;
245 let mplace = self.force_allocation(&src)?;
246 let len = mplace.len(self)?;
247 self.write_scalar(Scalar::from_machine_usize(len, self), &dest)?;
250 AddressOf(_, place) | Ref(_, _, place) => {
251 let src = self.eval_place(place)?;
252 let place = self.force_allocation(&src)?;
253 if place.layout.size.bytes() > 0 {
254 // definitely not a ZST
255 assert!(place.ptr.is_ptr(), "non-ZST places should be normalized to `Pointer`");
257 self.write_immediate(place.to_ref(), &dest)?;
260 NullaryOp(mir::NullOp::Box, _) => {
261 M::box_alloc(self, &dest)?;
264 NullaryOp(mir::NullOp::SizeOf, ty) => {
265 let ty = self.subst_from_current_frame_and_normalize_erasing_regions(ty);
266 let layout = self.layout_of(ty)?;
267 if layout.is_unsized() {
268 // FIXME: This should be a span_bug (#80742)
269 self.tcx.sess.delay_span_bug(
270 self.frame().current_span(),
271 &format!("SizeOf nullary MIR operator called for unsized type {}", ty),
273 throw_inval!(SizeOfUnsizedType(ty));
275 self.write_scalar(Scalar::from_machine_usize(layout.size.bytes(), self), &dest)?;
278 Cast(cast_kind, ref operand, cast_ty) => {
279 let src = self.eval_operand(operand, None)?;
280 let cast_ty = self.subst_from_current_frame_and_normalize_erasing_regions(cast_ty);
281 self.cast(&src, cast_kind, cast_ty, &dest)?;
284 Discriminant(place) => {
285 let op = self.eval_place_to_op(place, None)?;
286 let discr_val = self.read_discriminant(&op)?.0;
287 self.write_scalar(discr_val, &dest)?;
291 trace!("{:?}", self.dump_place(*dest));
296 fn terminator(&mut self, terminator: &mir::Terminator<'tcx>) -> InterpResult<'tcx> {
297 info!("{:?}", terminator.kind);
299 self.eval_terminator(terminator)?;
300 if !self.stack().is_empty() {
301 if let Ok(loc) = self.frame().loc {
302 info!("// executing {:?}", loc.block);