rustc_const_eval/interpret/step.rs
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//! This module contains the `InterpCx` methods for executing a single step of the interpreter.
//!
//! The main entry point is the `step` method.
use either::Either;
use rustc_abi::{FIRST_VARIANT, FieldIdx};
use rustc_index::IndexSlice;
use rustc_middle::ty::layout::FnAbiOf;
use rustc_middle::ty::{self, Instance, Ty};
use rustc_middle::{bug, mir, span_bug};
use rustc_span::source_map::Spanned;
use rustc_target::callconv::FnAbi;
use tracing::{info, instrument, trace};
use super::{
FnArg, FnVal, ImmTy, Immediate, InterpCx, InterpResult, Machine, MemPlaceMeta, PlaceTy,
Projectable, Scalar, interp_ok, throw_ub,
};
use crate::util;
struct EvaluatedCalleeAndArgs<'tcx, M: Machine<'tcx>> {
callee: FnVal<'tcx, M::ExtraFnVal>,
args: Vec<FnArg<'tcx, M::Provenance>>,
fn_sig: ty::FnSig<'tcx>,
fn_abi: &'tcx FnAbi<'tcx, Ty<'tcx>>,
/// True if the function is marked as `#[track_caller]` ([`ty::InstanceKind::requires_caller_location`])
with_caller_location: bool,
}
impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
/// Returns `true` as long as there are more things to do.
///
/// This is used by [priroda](https://github.com/oli-obk/priroda)
///
/// This is marked `#inline(always)` to work around adversarial codegen when `opt-level = 3`
#[inline(always)]
pub fn step(&mut self) -> InterpResult<'tcx, bool> {
if self.stack().is_empty() {
return interp_ok(false);
}
let Either::Left(loc) = self.frame().loc else {
// We are unwinding and this fn has no cleanup code.
// Just go on unwinding.
trace!("unwinding: skipping frame");
self.return_from_current_stack_frame(/* unwinding */ true)?;
return interp_ok(true);
};
let basic_block = &self.body().basic_blocks[loc.block];
if let Some(stmt) = basic_block.statements.get(loc.statement_index) {
let old_frames = self.frame_idx();
self.eval_statement(stmt)?;
// Make sure we are not updating `statement_index` of the wrong frame.
assert_eq!(old_frames, self.frame_idx());
// Advance the program counter.
self.frame_mut().loc.as_mut().left().unwrap().statement_index += 1;
return interp_ok(true);
}
M::before_terminator(self)?;
let terminator = basic_block.terminator();
self.eval_terminator(terminator)?;
if !self.stack().is_empty() {
if let Either::Left(loc) = self.frame().loc {
info!("// executing {:?}", loc.block);
}
}
interp_ok(true)
}
/// Runs the interpretation logic for the given `mir::Statement` at the current frame and
/// statement counter.
///
/// This does NOT move the statement counter forward, the caller has to do that!
pub fn eval_statement(&mut self, stmt: &mir::Statement<'tcx>) -> InterpResult<'tcx> {
info!("{:?}", stmt);
use rustc_middle::mir::StatementKind::*;
match &stmt.kind {
Assign(box (place, rvalue)) => self.eval_rvalue_into_place(rvalue, *place)?,
SetDiscriminant { place, variant_index } => {
let dest = self.eval_place(**place)?;
self.write_discriminant(*variant_index, &dest)?;
}
Deinit(place) => {
let dest = self.eval_place(**place)?;
self.write_uninit(&dest)?;
}
// Mark locals as alive
StorageLive(local) => {
self.storage_live(*local)?;
}
// Mark locals as dead
StorageDead(local) => {
self.storage_dead(*local)?;
}
// No dynamic semantics attached to `FakeRead`; MIR
// interpreter is solely intended for borrowck'ed code.
FakeRead(..) => {}
// Stacked Borrows.
Retag(kind, place) => {
let dest = self.eval_place(**place)?;
M::retag_place_contents(self, *kind, &dest)?;
}
Intrinsic(box intrinsic) => self.eval_nondiverging_intrinsic(intrinsic)?,
// Evaluate the place expression, without reading from it.
PlaceMention(box place) => {
let _ = self.eval_place(*place)?;
}
// This exists purely to guide borrowck lifetime inference, and does not have
// an operational effect.
AscribeUserType(..) => {}
// Currently, Miri discards Coverage statements. Coverage statements are only injected
// via an optional compile time MIR pass and have no side effects. Since Coverage
// statements don't exist at the source level, it is safe for Miri to ignore them, even
// for undefined behavior (UB) checks.
//
// A coverage counter inside a const expression (for example, a counter injected in a
// const function) is discarded when the const is evaluated at compile time. Whether
// this should change, and/or how to implement a const eval counter, is a subject of the
// following issue:
//
// FIXME(#73156): Handle source code coverage in const eval
Coverage(..) => {}
ConstEvalCounter => {
M::increment_const_eval_counter(self)?;
}
// Defined to do nothing. These are added by optimization passes, to avoid changing the
// size of MIR constantly.
Nop => {}
// Only used for temporary lifetime lints
BackwardIncompatibleDropHint { .. } => {}
}
interp_ok(())
}
/// Evaluate an assignment statement.
///
/// There is no separate `eval_rvalue` function. Instead, the code for handling each rvalue
/// type writes its results directly into the memory specified by the place.
pub fn eval_rvalue_into_place(
&mut self,
rvalue: &mir::Rvalue<'tcx>,
place: mir::Place<'tcx>,
) -> InterpResult<'tcx> {
let dest = self.eval_place(place)?;
// FIXME: ensure some kind of non-aliasing between LHS and RHS?
// Also see https://github.com/rust-lang/rust/issues/68364.
use rustc_middle::mir::Rvalue::*;
match *rvalue {
ThreadLocalRef(did) => {
let ptr = M::thread_local_static_pointer(self, did)?;
self.write_pointer(ptr, &dest)?;
}
Use(ref operand) => {
// Avoid recomputing the layout
let op = self.eval_operand(operand, Some(dest.layout))?;
self.copy_op(&op, &dest)?;
}
CopyForDeref(place) => {
let op = self.eval_place_to_op(place, Some(dest.layout))?;
self.copy_op(&op, &dest)?;
}
BinaryOp(bin_op, box (ref left, ref right)) => {
let layout = util::binop_left_homogeneous(bin_op).then_some(dest.layout);
let left = self.read_immediate(&self.eval_operand(left, layout)?)?;
let layout = util::binop_right_homogeneous(bin_op).then_some(left.layout);
let right = self.read_immediate(&self.eval_operand(right, layout)?)?;
let result = self.binary_op(bin_op, &left, &right)?;
assert_eq!(result.layout, dest.layout, "layout mismatch for result of {bin_op:?}");
self.write_immediate(*result, &dest)?;
}
UnaryOp(un_op, ref operand) => {
// The operand always has the same type as the result.
let val = self.read_immediate(&self.eval_operand(operand, Some(dest.layout))?)?;
let result = self.unary_op(un_op, &val)?;
assert_eq!(result.layout, dest.layout, "layout mismatch for result of {un_op:?}");
self.write_immediate(*result, &dest)?;
}
NullaryOp(null_op, ty) => {
let ty = self.instantiate_from_current_frame_and_normalize_erasing_regions(ty)?;
let val = self.nullary_op(null_op, ty)?;
self.write_immediate(*val, &dest)?;
}
Aggregate(box ref kind, ref operands) => {
self.write_aggregate(kind, operands, &dest)?;
}
Repeat(ref operand, _) => {
self.write_repeat(operand, &dest)?;
}
Len(place) => {
let src = self.eval_place(place)?;
let len = src.len(self)?;
self.write_scalar(Scalar::from_target_usize(len, self), &dest)?;
}
Ref(_, borrow_kind, place) => {
let src = self.eval_place(place)?;
let place = self.force_allocation(&src)?;
let val = ImmTy::from_immediate(place.to_ref(self), dest.layout);
// A fresh reference was created, make sure it gets retagged.
let val = M::retag_ptr_value(
self,
if borrow_kind.allows_two_phase_borrow() {
mir::RetagKind::TwoPhase
} else {
mir::RetagKind::Default
},
&val,
)?;
self.write_immediate(*val, &dest)?;
}
RawPtr(_, place) => {
// Figure out whether this is an addr_of of an already raw place.
let place_base_raw = if place.is_indirect_first_projection() {
let ty = self.frame().body.local_decls[place.local].ty;
ty.is_unsafe_ptr()
} else {
// Not a deref, and thus not raw.
false
};
let src = self.eval_place(place)?;
let place = self.force_allocation(&src)?;
let mut val = ImmTy::from_immediate(place.to_ref(self), dest.layout);
if !place_base_raw {
// If this was not already raw, it needs retagging.
val = M::retag_ptr_value(self, mir::RetagKind::Raw, &val)?;
}
self.write_immediate(*val, &dest)?;
}
ShallowInitBox(ref operand, _) => {
let src = self.eval_operand(operand, None)?;
let v = self.read_immediate(&src)?;
self.write_immediate(*v, &dest)?;
}
Cast(cast_kind, ref operand, cast_ty) => {
let src = self.eval_operand(operand, None)?;
let cast_ty =
self.instantiate_from_current_frame_and_normalize_erasing_regions(cast_ty)?;
self.cast(&src, cast_kind, cast_ty, &dest)?;
}
Discriminant(place) => {
let op = self.eval_place_to_op(place, None)?;
let variant = self.read_discriminant(&op)?;
let discr = self.discriminant_for_variant(op.layout.ty, variant)?;
self.write_immediate(*discr, &dest)?;
}
}
trace!("{:?}", self.dump_place(&dest));
interp_ok(())
}
/// Writes the aggregate to the destination.
#[instrument(skip(self), level = "trace")]
fn write_aggregate(
&mut self,
kind: &mir::AggregateKind<'tcx>,
operands: &IndexSlice<FieldIdx, mir::Operand<'tcx>>,
dest: &PlaceTy<'tcx, M::Provenance>,
) -> InterpResult<'tcx> {
self.write_uninit(dest)?; // make sure all the padding ends up as uninit
let (variant_index, variant_dest, active_field_index) = match *kind {
mir::AggregateKind::Adt(_, variant_index, _, _, active_field_index) => {
let variant_dest = self.project_downcast(dest, variant_index)?;
(variant_index, variant_dest, active_field_index)
}
mir::AggregateKind::RawPtr(..) => {
// Pointers don't have "fields" in the normal sense, so the
// projection-based code below would either fail in projection
// or in type mismatches. Instead, build an `Immediate` from
// the parts and write that to the destination.
let [data, meta] = &operands.raw else {
bug!("{kind:?} should have 2 operands, had {operands:?}");
};
let data = self.eval_operand(data, None)?;
let data = self.read_pointer(&data)?;
let meta = self.eval_operand(meta, None)?;
let meta = if meta.layout.is_zst() {
MemPlaceMeta::None
} else {
MemPlaceMeta::Meta(self.read_scalar(&meta)?)
};
let ptr_imm = Immediate::new_pointer_with_meta(data, meta, self);
let ptr = ImmTy::from_immediate(ptr_imm, dest.layout);
self.copy_op(&ptr, dest)?;
return interp_ok(());
}
_ => (FIRST_VARIANT, dest.clone(), None),
};
if active_field_index.is_some() {
assert_eq!(operands.len(), 1);
}
for (field_index, operand) in operands.iter_enumerated() {
let field_index = active_field_index.unwrap_or(field_index);
let field_dest = self.project_field(&variant_dest, field_index.as_usize())?;
let op = self.eval_operand(operand, Some(field_dest.layout))?;
self.copy_op(&op, &field_dest)?;
}
self.write_discriminant(variant_index, dest)
}
/// Repeats `operand` into the destination. `dest` must have array type, and that type
/// determines how often `operand` is repeated.
fn write_repeat(
&mut self,
operand: &mir::Operand<'tcx>,
dest: &PlaceTy<'tcx, M::Provenance>,
) -> InterpResult<'tcx> {
let src = self.eval_operand(operand, None)?;
assert!(src.layout.is_sized());
let dest = self.force_allocation(&dest)?;
let length = dest.len(self)?;
if length == 0 {
// Nothing to copy... but let's still make sure that `dest` as a place is valid.
self.get_place_alloc_mut(&dest)?;
} else {
// Write the src to the first element.
let first = self.project_index(&dest, 0)?;
self.copy_op(&src, &first)?;
// This is performance-sensitive code for big static/const arrays! So we
// avoid writing each operand individually and instead just make many copies
// of the first element.
let elem_size = first.layout.size;
let first_ptr = first.ptr();
let rest_ptr = first_ptr.wrapping_offset(elem_size, self);
// No alignment requirement since `copy_op` above already checked it.
self.mem_copy_repeatedly(
first_ptr,
rest_ptr,
elem_size,
length - 1,
/*nonoverlapping:*/ true,
)?;
}
interp_ok(())
}
/// Evaluate the arguments of a function call
fn eval_fn_call_argument(
&self,
op: &mir::Operand<'tcx>,
) -> InterpResult<'tcx, FnArg<'tcx, M::Provenance>> {
interp_ok(match op {
mir::Operand::Copy(_) | mir::Operand::Constant(_) => {
// Make a regular copy.
let op = self.eval_operand(op, None)?;
FnArg::Copy(op)
}
mir::Operand::Move(place) => {
// If this place lives in memory, preserve its location.
// We call `place_to_op` which will be an `MPlaceTy` whenever there exists
// an mplace for this place. (This is in contrast to `PlaceTy::as_mplace_or_local`
// which can return a local even if that has an mplace.)
let place = self.eval_place(*place)?;
let op = self.place_to_op(&place)?;
match op.as_mplace_or_imm() {
Either::Left(mplace) => FnArg::InPlace(mplace),
Either::Right(_imm) => {
// This argument doesn't live in memory, so there's no place
// to make inaccessible during the call.
// We rely on there not being any stray `PlaceTy` that would let the
// caller directly access this local!
// This is also crucial for tail calls, where we want the `FnArg` to
// stay valid when the old stack frame gets popped.
FnArg::Copy(op)
}
}
}
})
}
/// Shared part of `Call` and `TailCall` implementation — finding and evaluating all the
/// necessary information about callee and arguments to make a call.
fn eval_callee_and_args(
&self,
terminator: &mir::Terminator<'tcx>,
func: &mir::Operand<'tcx>,
args: &[Spanned<mir::Operand<'tcx>>],
) -> InterpResult<'tcx, EvaluatedCalleeAndArgs<'tcx, M>> {
let func = self.eval_operand(func, None)?;
let args = args
.iter()
.map(|arg| self.eval_fn_call_argument(&arg.node))
.collect::<InterpResult<'tcx, Vec<_>>>()?;
let fn_sig_binder = func.layout.ty.fn_sig(*self.tcx);
let fn_sig = self.tcx.normalize_erasing_late_bound_regions(self.typing_env, fn_sig_binder);
let extra_args = &args[fn_sig.inputs().len()..];
let extra_args =
self.tcx.mk_type_list_from_iter(extra_args.iter().map(|arg| arg.layout().ty));
let (callee, fn_abi, with_caller_location) = match *func.layout.ty.kind() {
ty::FnPtr(..) => {
let fn_ptr = self.read_pointer(&func)?;
let fn_val = self.get_ptr_fn(fn_ptr)?;
(fn_val, self.fn_abi_of_fn_ptr(fn_sig_binder, extra_args)?, false)
}
ty::FnDef(def_id, args) => {
let instance = self.resolve(def_id, args)?;
(
FnVal::Instance(instance),
self.fn_abi_of_instance(instance, extra_args)?,
instance.def.requires_caller_location(*self.tcx),
)
}
_ => {
span_bug!(terminator.source_info.span, "invalid callee of type {}", func.layout.ty)
}
};
interp_ok(EvaluatedCalleeAndArgs { callee, args, fn_sig, fn_abi, with_caller_location })
}
fn eval_terminator(&mut self, terminator: &mir::Terminator<'tcx>) -> InterpResult<'tcx> {
info!("{:?}", terminator.kind);
use rustc_middle::mir::TerminatorKind::*;
match terminator.kind {
Return => {
self.return_from_current_stack_frame(/* unwinding */ false)?
}
Goto { target } => self.go_to_block(target),
SwitchInt { ref discr, ref targets } => {
let discr = self.read_immediate(&self.eval_operand(discr, None)?)?;
trace!("SwitchInt({:?})", *discr);
// Branch to the `otherwise` case by default, if no match is found.
let mut target_block = targets.otherwise();
for (const_int, target) in targets.iter() {
// Compare using MIR BinOp::Eq, to also support pointer values.
// (Avoiding `self.binary_op` as that does some redundant layout computation.)
let res = self.binary_op(
mir::BinOp::Eq,
&discr,
&ImmTy::from_uint(const_int, discr.layout),
)?;
if res.to_scalar().to_bool()? {
target_block = target;
break;
}
}
self.go_to_block(target_block);
}
Call {
ref func,
ref args,
destination,
target,
unwind,
call_source: _,
fn_span: _,
} => {
let old_stack = self.frame_idx();
let old_loc = self.frame().loc;
let EvaluatedCalleeAndArgs { callee, args, fn_sig, fn_abi, with_caller_location } =
self.eval_callee_and_args(terminator, func, args)?;
let destination = self.force_allocation(&self.eval_place(destination)?)?;
self.init_fn_call(
callee,
(fn_sig.abi, fn_abi),
&args,
with_caller_location,
&destination,
target,
if fn_abi.can_unwind { unwind } else { mir::UnwindAction::Unreachable },
)?;
// Sanity-check that `eval_fn_call` either pushed a new frame or
// did a jump to another block.
if self.frame_idx() == old_stack && self.frame().loc == old_loc {
span_bug!(terminator.source_info.span, "evaluating this call made no progress");
}
}
TailCall { ref func, ref args, fn_span: _ } => {
let old_frame_idx = self.frame_idx();
let EvaluatedCalleeAndArgs { callee, args, fn_sig, fn_abi, with_caller_location } =
self.eval_callee_and_args(terminator, func, args)?;
self.init_fn_tail_call(callee, (fn_sig.abi, fn_abi), &args, with_caller_location)?;
if self.frame_idx() != old_frame_idx {
span_bug!(
terminator.source_info.span,
"evaluating this tail call pushed a new stack frame"
);
}
}
Drop { place, target, unwind, replace: _ } => {
let place = self.eval_place(place)?;
let instance = Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
if let ty::InstanceKind::DropGlue(_, None) = instance.def {
// This is the branch we enter if and only if the dropped type has no drop glue
// whatsoever. This can happen as a result of monomorphizing a drop of a
// generic. In order to make sure that generic and non-generic code behaves
// roughly the same (and in keeping with Mir semantics) we do nothing here.
self.go_to_block(target);
return interp_ok(());
}
trace!("TerminatorKind::drop: {:?}, type {}", place, place.layout.ty);
self.init_drop_in_place_call(&place, instance, target, unwind)?;
}
Assert { ref cond, expected, ref msg, target, unwind } => {
let ignored =
M::ignore_optional_overflow_checks(self) && msg.is_optional_overflow_check();
let cond_val = self.read_scalar(&self.eval_operand(cond, None)?)?.to_bool()?;
if ignored || expected == cond_val {
self.go_to_block(target);
} else {
M::assert_panic(self, msg, unwind)?;
}
}
UnwindTerminate(reason) => {
M::unwind_terminate(self, reason)?;
}
// When we encounter Resume, we've finished unwinding
// cleanup for the current stack frame. We pop it in order
// to continue unwinding the next frame
UnwindResume => {
trace!("unwinding: resuming from cleanup");
// By definition, a Resume terminator means
// that we're unwinding
self.return_from_current_stack_frame(/* unwinding */ true)?;
return interp_ok(());
}
// It is UB to ever encounter this.
Unreachable => throw_ub!(Unreachable),
// These should never occur for MIR we actually run.
FalseEdge { .. } | FalseUnwind { .. } | Yield { .. } | CoroutineDrop => span_bug!(
terminator.source_info.span,
"{:#?} should have been eliminated by MIR pass",
terminator.kind
),
InlineAsm { template, ref operands, options, ref targets, .. } => {
M::eval_inline_asm(self, template, operands, options, targets)?;
}
}
interp_ok(())
}
}