rustc_const_eval/const_eval/machine.rs
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use std::borrow::{Borrow, Cow};
use std::fmt;
use std::hash::Hash;
use rustc_abi::{Align, ExternAbi, Size};
use rustc_ast::Mutability;
use rustc_data_structures::fx::{FxHashMap, FxIndexMap, IndexEntry};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::{self as hir, CRATE_HIR_ID, LangItem};
use rustc_middle::mir::AssertMessage;
use rustc_middle::mir::interpret::ReportedErrorInfo;
use rustc_middle::query::TyCtxtAt;
use rustc_middle::ty::layout::{HasTypingEnv, TyAndLayout};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::{bug, mir};
use rustc_span::Span;
use rustc_span::symbol::{Symbol, sym};
use tracing::debug;
use super::error::*;
use crate::errors::{LongRunning, LongRunningWarn};
use crate::fluent_generated as fluent;
use crate::interpret::{
self, AllocId, AllocRange, ConstAllocation, CtfeProvenance, FnArg, Frame, GlobalAlloc, ImmTy,
InterpCx, InterpResult, MPlaceTy, OpTy, RangeSet, Scalar, compile_time_machine, interp_ok,
throw_exhaust, throw_inval, throw_ub, throw_ub_custom, throw_unsup, throw_unsup_format,
};
/// When hitting this many interpreted terminators we emit a deny by default lint
/// that notfies the user that their constant takes a long time to evaluate. If that's
/// what they intended, they can just allow the lint.
const LINT_TERMINATOR_LIMIT: usize = 2_000_000;
/// The limit used by `-Z tiny-const-eval-limit`. This smaller limit is useful for internal
/// tests not needing to run 30s or more to show some behaviour.
const TINY_LINT_TERMINATOR_LIMIT: usize = 20;
/// After this many interpreted terminators, we start emitting progress indicators at every
/// power of two of interpreted terminators.
const PROGRESS_INDICATOR_START: usize = 4_000_000;
/// Extra machine state for CTFE, and the Machine instance.
//
// Should be public because out-of-tree rustc consumers need this
// if they want to interact with constant values.
pub struct CompileTimeMachine<'tcx> {
/// The number of terminators that have been evaluated.
///
/// This is used to produce lints informing the user that the compiler is not stuck.
/// Set to `usize::MAX` to never report anything.
pub(super) num_evaluated_steps: usize,
/// The virtual call stack.
pub(super) stack: Vec<Frame<'tcx>>,
/// Pattern matching on consts with references would be unsound if those references
/// could point to anything mutable. Therefore, when evaluating consts and when constructing valtrees,
/// we ensure that only immutable global memory can be accessed.
pub(super) can_access_mut_global: CanAccessMutGlobal,
/// Whether to check alignment during evaluation.
pub(super) check_alignment: CheckAlignment,
/// If `Some`, we are evaluating the initializer of the static with the given `LocalDefId`,
/// storing the result in the given `AllocId`.
/// Used to prevent reads from a static's base allocation, as that may allow for self-initialization loops.
pub(crate) static_root_ids: Option<(AllocId, LocalDefId)>,
/// A cache of "data range" computations for unions (i.e., the offsets of non-padding bytes).
union_data_ranges: FxHashMap<Ty<'tcx>, RangeSet>,
}
#[derive(Copy, Clone)]
pub enum CheckAlignment {
/// Ignore all alignment requirements.
/// This is mainly used in interning.
No,
/// Hard error when dereferencing a misaligned pointer.
Error,
}
#[derive(Copy, Clone, PartialEq)]
pub(crate) enum CanAccessMutGlobal {
No,
Yes,
}
impl From<bool> for CanAccessMutGlobal {
fn from(value: bool) -> Self {
if value { Self::Yes } else { Self::No }
}
}
impl<'tcx> CompileTimeMachine<'tcx> {
pub(crate) fn new(
can_access_mut_global: CanAccessMutGlobal,
check_alignment: CheckAlignment,
) -> Self {
CompileTimeMachine {
num_evaluated_steps: 0,
stack: Vec::new(),
can_access_mut_global,
check_alignment,
static_root_ids: None,
union_data_ranges: FxHashMap::default(),
}
}
}
impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxIndexMap<K, V> {
#[inline(always)]
fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
where
K: Borrow<Q>,
{
FxIndexMap::contains_key(self, k)
}
#[inline(always)]
fn contains_key_ref<Q: ?Sized + Hash + Eq>(&self, k: &Q) -> bool
where
K: Borrow<Q>,
{
FxIndexMap::contains_key(self, k)
}
#[inline(always)]
fn insert(&mut self, k: K, v: V) -> Option<V> {
FxIndexMap::insert(self, k, v)
}
#[inline(always)]
fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
where
K: Borrow<Q>,
{
// FIXME(#120456) - is `swap_remove` correct?
FxIndexMap::swap_remove(self, k)
}
#[inline(always)]
fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
self.iter().filter_map(move |(k, v)| f(k, v)).collect()
}
#[inline(always)]
fn get_or<E>(&self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&V, E> {
match self.get(&k) {
Some(v) => Ok(v),
None => {
vacant()?;
bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
}
}
}
#[inline(always)]
fn get_mut_or<E>(&mut self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&mut V, E> {
match self.entry(k) {
IndexEntry::Occupied(e) => Ok(e.into_mut()),
IndexEntry::Vacant(e) => {
let v = vacant()?;
Ok(e.insert(v))
}
}
}
}
pub type CompileTimeInterpCx<'tcx> = InterpCx<'tcx, CompileTimeMachine<'tcx>>;
#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum MemoryKind {
Heap,
}
impl fmt::Display for MemoryKind {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
MemoryKind::Heap => write!(f, "heap allocation"),
}
}
}
impl interpret::MayLeak for MemoryKind {
#[inline(always)]
fn may_leak(self) -> bool {
match self {
MemoryKind::Heap => false,
}
}
}
impl interpret::MayLeak for ! {
#[inline(always)]
fn may_leak(self) -> bool {
// `self` is uninhabited
self
}
}
impl<'tcx> CompileTimeInterpCx<'tcx> {
fn location_triple_for_span(&self, span: Span) -> (Symbol, u32, u32) {
let topmost = span.ctxt().outer_expn().expansion_cause().unwrap_or(span);
let caller = self.tcx.sess.source_map().lookup_char_pos(topmost.lo());
use rustc_session::RemapFileNameExt;
use rustc_session::config::RemapPathScopeComponents;
(
Symbol::intern(
&caller
.file
.name
.for_scope(self.tcx.sess, RemapPathScopeComponents::DIAGNOSTICS)
.to_string_lossy(),
),
u32::try_from(caller.line).unwrap(),
u32::try_from(caller.col_display).unwrap().checked_add(1).unwrap(),
)
}
/// "Intercept" a function call, because we have something special to do for it.
/// All `#[rustc_do_not_const_check]` functions MUST be hooked here.
/// If this returns `Some` function, which may be `instance` or a different function with
/// compatible arguments, then evaluation should continue with that function.
/// If this returns `None`, the function call has been handled and the function has returned.
fn hook_special_const_fn(
&mut self,
instance: ty::Instance<'tcx>,
args: &[FnArg<'tcx>],
_dest: &MPlaceTy<'tcx>,
_ret: Option<mir::BasicBlock>,
) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
let def_id = instance.def_id();
if self.tcx.has_attr(def_id, sym::rustc_const_panic_str)
|| self.tcx.is_lang_item(def_id, LangItem::BeginPanic)
{
let args = self.copy_fn_args(args);
// &str or &&str
assert!(args.len() == 1);
let mut msg_place = self.deref_pointer(&args[0])?;
while msg_place.layout.ty.is_ref() {
msg_place = self.deref_pointer(&msg_place)?;
}
let msg = Symbol::intern(self.read_str(&msg_place)?);
let span = self.find_closest_untracked_caller_location();
let (file, line, col) = self.location_triple_for_span(span);
return Err(ConstEvalErrKind::Panic { msg, file, line, col }).into();
} else if self.tcx.is_lang_item(def_id, LangItem::PanicFmt) {
// For panic_fmt, call const_panic_fmt instead.
let const_def_id = self.tcx.require_lang_item(LangItem::ConstPanicFmt, None);
// FIXME(@lcnr): why does this use an empty env if we've got a `param_env` right here.
let new_instance = ty::Instance::expect_resolve(
*self.tcx,
ty::TypingEnv::fully_monomorphized(),
const_def_id,
instance.args,
self.cur_span(),
);
return interp_ok(Some(new_instance));
}
interp_ok(Some(instance))
}
/// See documentation on the `ptr_guaranteed_cmp` intrinsic.
/// Returns `2` if the result is unknown.
/// Returns `1` if the pointers are guaranteed equal.
/// Returns `0` if the pointers are guaranteed inequal.
///
/// Note that this intrinsic is exposed on stable for comparison with null. In other words, any
/// change to this function that affects comparison with null is insta-stable!
fn guaranteed_cmp(&mut self, a: Scalar, b: Scalar) -> InterpResult<'tcx, u8> {
interp_ok(match (a, b) {
// Comparisons between integers are always known.
(Scalar::Int { .. }, Scalar::Int { .. }) => {
if a == b {
1
} else {
0
}
}
// Comparisons of abstract pointers with null pointers are known if the pointer
// is in bounds, because if they are in bounds, the pointer can't be null.
// Inequality with integers other than null can never be known for sure.
(Scalar::Int(int), ptr @ Scalar::Ptr(..))
| (ptr @ Scalar::Ptr(..), Scalar::Int(int))
if int.is_null() && !self.scalar_may_be_null(ptr)? =>
{
0
}
// Equality with integers can never be known for sure.
(Scalar::Int { .. }, Scalar::Ptr(..)) | (Scalar::Ptr(..), Scalar::Int { .. }) => 2,
// FIXME: return a `1` for when both sides are the same pointer, *except* that
// some things (like functions and vtables) do not have stable addresses
// so we need to be careful around them (see e.g. #73722).
// FIXME: return `0` for at least some comparisons where we can reliably
// determine the result of runtime inequality tests at compile-time.
// Examples include comparison of addresses in different static items.
(Scalar::Ptr(..), Scalar::Ptr(..)) => 2,
})
}
}
impl<'tcx> CompileTimeMachine<'tcx> {
#[inline(always)]
/// Find the first stack frame that is within the current crate, if any.
/// Otherwise, return the crate's HirId
pub fn best_lint_scope(&self, tcx: TyCtxt<'tcx>) -> hir::HirId {
self.stack.iter().find_map(|frame| frame.lint_root(tcx)).unwrap_or(CRATE_HIR_ID)
}
}
impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
compile_time_machine!(<'tcx>);
type MemoryKind = MemoryKind;
const PANIC_ON_ALLOC_FAIL: bool = false; // will be raised as a proper error
#[inline(always)]
fn enforce_alignment(ecx: &InterpCx<'tcx, Self>) -> bool {
matches!(ecx.machine.check_alignment, CheckAlignment::Error)
}
#[inline(always)]
fn enforce_validity(ecx: &InterpCx<'tcx, Self>, layout: TyAndLayout<'tcx>) -> bool {
ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks || layout.is_uninhabited()
}
fn load_mir(
ecx: &InterpCx<'tcx, Self>,
instance: ty::InstanceKind<'tcx>,
) -> InterpResult<'tcx, &'tcx mir::Body<'tcx>> {
match instance {
ty::InstanceKind::Item(def) => interp_ok(ecx.tcx.mir_for_ctfe(def)),
_ => interp_ok(ecx.tcx.instance_mir(instance)),
}
}
fn find_mir_or_eval_fn(
ecx: &mut InterpCx<'tcx, Self>,
orig_instance: ty::Instance<'tcx>,
_abi: ExternAbi,
args: &[FnArg<'tcx>],
dest: &MPlaceTy<'tcx>,
ret: Option<mir::BasicBlock>,
_unwind: mir::UnwindAction, // unwinding is not supported in consts
) -> InterpResult<'tcx, Option<(&'tcx mir::Body<'tcx>, ty::Instance<'tcx>)>> {
debug!("find_mir_or_eval_fn: {:?}", orig_instance);
// Replace some functions.
let Some(instance) = ecx.hook_special_const_fn(orig_instance, args, dest, ret)? else {
// Call has already been handled.
return interp_ok(None);
};
// Only check non-glue functions
if let ty::InstanceKind::Item(def) = instance.def {
// Execution might have wandered off into other crates, so we cannot do a stability-
// sensitive check here. But we can at least rule out functions that are not const at
// all. That said, we have to allow calling functions inside a trait marked with
// #[const_trait]. These *are* const-checked!
// FIXME(const_trait_impl): why does `is_const_fn` not classify them as const?
if (!ecx.tcx.is_const_fn(def) && !ecx.tcx.is_const_default_method(def))
|| ecx.tcx.has_attr(def, sym::rustc_do_not_const_check)
{
// We certainly do *not* want to actually call the fn
// though, so be sure we return here.
throw_unsup_format!("calling non-const function `{}`", instance)
}
}
// This is a const fn. Call it.
// In case of replacement, we return the *original* instance to make backtraces work out
// (and we hope this does not confuse the FnAbi checks too much).
interp_ok(Some((ecx.load_mir(instance.def, None)?, orig_instance)))
}
fn panic_nounwind(ecx: &mut InterpCx<'tcx, Self>, msg: &str) -> InterpResult<'tcx> {
let msg = Symbol::intern(msg);
let span = ecx.find_closest_untracked_caller_location();
let (file, line, col) = ecx.location_triple_for_span(span);
Err(ConstEvalErrKind::Panic { msg, file, line, col }).into()
}
fn call_intrinsic(
ecx: &mut InterpCx<'tcx, Self>,
instance: ty::Instance<'tcx>,
args: &[OpTy<'tcx>],
dest: &MPlaceTy<'tcx, Self::Provenance>,
target: Option<mir::BasicBlock>,
_unwind: mir::UnwindAction,
) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
// Shared intrinsics.
if ecx.eval_intrinsic(instance, args, dest, target)? {
return interp_ok(None);
}
let intrinsic_name = ecx.tcx.item_name(instance.def_id());
// CTFE-specific intrinsics.
match intrinsic_name {
sym::ptr_guaranteed_cmp => {
let a = ecx.read_scalar(&args[0])?;
let b = ecx.read_scalar(&args[1])?;
let cmp = ecx.guaranteed_cmp(a, b)?;
ecx.write_scalar(Scalar::from_u8(cmp), dest)?;
}
sym::const_allocate => {
let size = ecx.read_scalar(&args[0])?.to_target_usize(ecx)?;
let align = ecx.read_scalar(&args[1])?.to_target_usize(ecx)?;
let align = match Align::from_bytes(align) {
Ok(a) => a,
Err(err) => throw_ub_custom!(
fluent::const_eval_invalid_align_details,
name = "const_allocate",
err_kind = err.diag_ident(),
align = err.align()
),
};
let ptr = ecx.allocate_ptr(
Size::from_bytes(size),
align,
interpret::MemoryKind::Machine(MemoryKind::Heap),
)?;
ecx.write_pointer(ptr, dest)?;
}
sym::const_deallocate => {
let ptr = ecx.read_pointer(&args[0])?;
let size = ecx.read_scalar(&args[1])?.to_target_usize(ecx)?;
let align = ecx.read_scalar(&args[2])?.to_target_usize(ecx)?;
let size = Size::from_bytes(size);
let align = match Align::from_bytes(align) {
Ok(a) => a,
Err(err) => throw_ub_custom!(
fluent::const_eval_invalid_align_details,
name = "const_deallocate",
err_kind = err.diag_ident(),
align = err.align()
),
};
// If an allocation is created in an another const,
// we don't deallocate it.
let (alloc_id, _, _) = ecx.ptr_get_alloc_id(ptr, 0)?;
let is_allocated_in_another_const = matches!(
ecx.tcx.try_get_global_alloc(alloc_id),
Some(interpret::GlobalAlloc::Memory(_))
);
if !is_allocated_in_another_const {
ecx.deallocate_ptr(
ptr,
Some((size, align)),
interpret::MemoryKind::Machine(MemoryKind::Heap),
)?;
}
}
// The intrinsic represents whether the value is known to the optimizer (LLVM).
// We're not doing any optimizations here, so there is no optimizer that could know the value.
// (We know the value here in the machine of course, but this is the runtime of that code,
// not the optimization stage.)
sym::is_val_statically_known => ecx.write_scalar(Scalar::from_bool(false), dest)?,
_ => {
// We haven't handled the intrinsic, let's see if we can use a fallback body.
if ecx.tcx.intrinsic(instance.def_id()).unwrap().must_be_overridden {
throw_unsup_format!(
"intrinsic `{intrinsic_name}` is not supported at compile-time"
);
}
return interp_ok(Some(ty::Instance {
def: ty::InstanceKind::Item(instance.def_id()),
args: instance.args,
}));
}
}
// Intrinsic is done, jump to next block.
ecx.return_to_block(target)?;
interp_ok(None)
}
fn assert_panic(
ecx: &mut InterpCx<'tcx, Self>,
msg: &AssertMessage<'tcx>,
_unwind: mir::UnwindAction,
) -> InterpResult<'tcx> {
use rustc_middle::mir::AssertKind::*;
// Convert `AssertKind<Operand>` to `AssertKind<Scalar>`.
let eval_to_int =
|op| ecx.read_immediate(&ecx.eval_operand(op, None)?).map(|x| x.to_const_int());
let err = match msg {
BoundsCheck { len, index } => {
let len = eval_to_int(len)?;
let index = eval_to_int(index)?;
BoundsCheck { len, index }
}
Overflow(op, l, r) => Overflow(*op, eval_to_int(l)?, eval_to_int(r)?),
OverflowNeg(op) => OverflowNeg(eval_to_int(op)?),
DivisionByZero(op) => DivisionByZero(eval_to_int(op)?),
RemainderByZero(op) => RemainderByZero(eval_to_int(op)?),
ResumedAfterReturn(coroutine_kind) => ResumedAfterReturn(*coroutine_kind),
ResumedAfterPanic(coroutine_kind) => ResumedAfterPanic(*coroutine_kind),
MisalignedPointerDereference { ref required, ref found } => {
MisalignedPointerDereference {
required: eval_to_int(required)?,
found: eval_to_int(found)?,
}
}
};
Err(ConstEvalErrKind::AssertFailure(err)).into()
}
fn binary_ptr_op(
_ecx: &InterpCx<'tcx, Self>,
_bin_op: mir::BinOp,
_left: &ImmTy<'tcx>,
_right: &ImmTy<'tcx>,
) -> InterpResult<'tcx, ImmTy<'tcx>> {
throw_unsup_format!("pointer arithmetic or comparison is not supported at compile-time");
}
fn increment_const_eval_counter(ecx: &mut InterpCx<'tcx, Self>) -> InterpResult<'tcx> {
// The step limit has already been hit in a previous call to `increment_const_eval_counter`.
if let Some(new_steps) = ecx.machine.num_evaluated_steps.checked_add(1) {
let (limit, start) = if ecx.tcx.sess.opts.unstable_opts.tiny_const_eval_limit {
(TINY_LINT_TERMINATOR_LIMIT, TINY_LINT_TERMINATOR_LIMIT)
} else {
(LINT_TERMINATOR_LIMIT, PROGRESS_INDICATOR_START)
};
ecx.machine.num_evaluated_steps = new_steps;
// By default, we have a *deny* lint kicking in after some time
// to ensure `loop {}` doesn't just go forever.
// In case that lint got reduced, in particular for `--cap-lint` situations, we also
// have a hard warning shown every now and then for really long executions.
if new_steps == limit {
// By default, we stop after a million steps, but the user can disable this lint
// to be able to run until the heat death of the universe or power loss, whichever
// comes first.
let hir_id = ecx.machine.best_lint_scope(*ecx.tcx);
let is_error = ecx
.tcx
.lint_level_at_node(
rustc_session::lint::builtin::LONG_RUNNING_CONST_EVAL,
hir_id,
)
.0
.is_error();
let span = ecx.cur_span();
ecx.tcx.emit_node_span_lint(
rustc_session::lint::builtin::LONG_RUNNING_CONST_EVAL,
hir_id,
span,
LongRunning { item_span: ecx.tcx.span },
);
// If this was a hard error, don't bother continuing evaluation.
if is_error {
let guard = ecx
.tcx
.dcx()
.span_delayed_bug(span, "The deny lint should have already errored");
throw_inval!(AlreadyReported(ReportedErrorInfo::allowed_in_infallible(guard)));
}
} else if new_steps > start && new_steps.is_power_of_two() {
// Only report after a certain number of terminators have been evaluated and the
// current number of evaluated terminators is a power of 2. The latter gives us a cheap
// way to implement exponential backoff.
let span = ecx.cur_span();
// We store a unique number in `force_duplicate` to evade `-Z deduplicate-diagnostics`.
// `new_steps` is guaranteed to be unique because `ecx.machine.num_evaluated_steps` is
// always increasing.
ecx.tcx.dcx().emit_warn(LongRunningWarn {
span,
item_span: ecx.tcx.span,
force_duplicate: new_steps,
});
}
}
interp_ok(())
}
#[inline(always)]
fn expose_provenance(
_ecx: &InterpCx<'tcx, Self>,
_provenance: Self::Provenance,
) -> InterpResult<'tcx> {
// This is only reachable with -Zunleash-the-miri-inside-of-you.
throw_unsup_format!("exposing pointers is not possible at compile-time")
}
#[inline(always)]
fn init_frame(
ecx: &mut InterpCx<'tcx, Self>,
frame: Frame<'tcx>,
) -> InterpResult<'tcx, Frame<'tcx>> {
// Enforce stack size limit. Add 1 because this is run before the new frame is pushed.
if !ecx.recursion_limit.value_within_limit(ecx.stack().len() + 1) {
throw_exhaust!(StackFrameLimitReached)
} else {
interp_ok(frame)
}
}
#[inline(always)]
fn stack<'a>(
ecx: &'a InterpCx<'tcx, Self>,
) -> &'a [Frame<'tcx, Self::Provenance, Self::FrameExtra>] {
&ecx.machine.stack
}
#[inline(always)]
fn stack_mut<'a>(
ecx: &'a mut InterpCx<'tcx, Self>,
) -> &'a mut Vec<Frame<'tcx, Self::Provenance, Self::FrameExtra>> {
&mut ecx.machine.stack
}
fn before_access_global(
_tcx: TyCtxtAt<'tcx>,
machine: &Self,
alloc_id: AllocId,
alloc: ConstAllocation<'tcx>,
_static_def_id: Option<DefId>,
is_write: bool,
) -> InterpResult<'tcx> {
let alloc = alloc.inner();
if is_write {
// Write access. These are never allowed, but we give a targeted error message.
match alloc.mutability {
Mutability::Not => throw_ub!(WriteToReadOnly(alloc_id)),
Mutability::Mut => Err(ConstEvalErrKind::ModifiedGlobal).into(),
}
} else {
// Read access. These are usually allowed, with some exceptions.
if machine.can_access_mut_global == CanAccessMutGlobal::Yes {
// Machine configuration allows us read from anything (e.g., `static` initializer).
interp_ok(())
} else if alloc.mutability == Mutability::Mut {
// Machine configuration does not allow us to read statics (e.g., `const`
// initializer).
Err(ConstEvalErrKind::ConstAccessesMutGlobal).into()
} else {
// Immutable global, this read is fine.
assert_eq!(alloc.mutability, Mutability::Not);
interp_ok(())
}
}
}
fn retag_ptr_value(
ecx: &mut InterpCx<'tcx, Self>,
_kind: mir::RetagKind,
val: &ImmTy<'tcx, CtfeProvenance>,
) -> InterpResult<'tcx, ImmTy<'tcx, CtfeProvenance>> {
// If it's a frozen shared reference that's not already immutable, potentially make it immutable.
// (Do nothing on `None` provenance, that cannot store immutability anyway.)
if let ty::Ref(_, ty, mutbl) = val.layout.ty.kind()
&& *mutbl == Mutability::Not
&& val
.to_scalar_and_meta()
.0
.to_pointer(ecx)?
.provenance
.is_some_and(|p| !p.immutable())
{
// That next check is expensive, that's why we have all the guards above.
let is_immutable = ty.is_freeze(*ecx.tcx, ecx.typing_env());
let place = ecx.ref_to_mplace(val)?;
let new_place = if is_immutable {
place.map_provenance(CtfeProvenance::as_immutable)
} else {
// Even if it is not immutable, remember that it is a shared reference.
// This allows it to become part of the final value of the constant.
// (See <https://github.com/rust-lang/rust/pull/128543> for why we allow this
// even when there is interior mutability.)
place.map_provenance(CtfeProvenance::as_shared_ref)
};
interp_ok(ImmTy::from_immediate(new_place.to_ref(ecx), val.layout))
} else {
interp_ok(val.clone())
}
}
fn before_memory_write(
_tcx: TyCtxtAt<'tcx>,
_machine: &mut Self,
_alloc_extra: &mut Self::AllocExtra,
(_alloc_id, immutable): (AllocId, bool),
range: AllocRange,
) -> InterpResult<'tcx> {
if range.size == Size::ZERO {
// Nothing to check.
return interp_ok(());
}
// Reject writes through immutable pointers.
if immutable {
return Err(ConstEvalErrKind::WriteThroughImmutablePointer).into();
}
// Everything else is fine.
interp_ok(())
}
fn before_alloc_read(ecx: &InterpCx<'tcx, Self>, alloc_id: AllocId) -> InterpResult<'tcx> {
// Check if this is the currently evaluated static.
if Some(alloc_id) == ecx.machine.static_root_ids.map(|(id, _)| id) {
return Err(ConstEvalErrKind::RecursiveStatic).into();
}
// If this is another static, make sure we fire off the query to detect cycles.
// But only do that when checks for static recursion are enabled.
if ecx.machine.static_root_ids.is_some() {
if let Some(GlobalAlloc::Static(def_id)) = ecx.tcx.try_get_global_alloc(alloc_id) {
if ecx.tcx.is_foreign_item(def_id) {
throw_unsup!(ExternStatic(def_id));
}
ecx.ctfe_query(|tcx| tcx.eval_static_initializer(def_id))?;
}
}
interp_ok(())
}
fn cached_union_data_range<'e>(
ecx: &'e mut InterpCx<'tcx, Self>,
ty: Ty<'tcx>,
compute_range: impl FnOnce() -> RangeSet,
) -> Cow<'e, RangeSet> {
if ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks {
Cow::Borrowed(ecx.machine.union_data_ranges.entry(ty).or_insert_with(compute_range))
} else {
// Don't bother caching, we're only doing one validation at the end anyway.
Cow::Owned(compute_range())
}
}
}
// Please do not add any code below the above `Machine` trait impl. I (oli-obk) plan more cleanups
// so we can end up having a file with just that impl, but for now, let's keep the impl discoverable
// at the bottom of this file.