1 // Not in interpret to make sure we do not use private implementation details
5 use std::borrow::{Borrow, Cow};
7 use std::collections::hash_map::Entry;
9 use rustc::hir::{self, def_id::DefId};
10 use rustc::hir::def::Def;
11 use rustc::mir::interpret::{ConstEvalErr, ErrorHandled};
13 use rustc::ty::{self, TyCtxt, query::TyCtxtAt};
14 use rustc::ty::layout::{self, LayoutOf, VariantIdx};
15 use rustc::ty::subst::Subst;
16 use rustc::traits::Reveal;
17 use rustc_data_structures::fx::FxHashMap;
18 use rustc::util::common::ErrorReported;
20 use syntax::ast::Mutability;
21 use syntax::source_map::{Span, DUMMY_SP};
23 use crate::interpret::{self,
24 PlaceTy, MPlaceTy, MemPlace, OpTy, ImmTy, Immediate, Scalar, Pointer,
26 EvalResult, EvalError, EvalErrorKind, GlobalId, EvalContext, StackPopCleanup,
27 Allocation, AllocId, MemoryKind,
28 snapshot, RefTracking,
31 /// Number of steps until the detector even starts doing anything.
32 /// Also, a warning is shown to the user when this number is reached.
33 const STEPS_UNTIL_DETECTOR_ENABLED: isize = 1_000_000;
34 /// The number of steps between loop detector snapshots.
35 /// Should be a power of two for performance reasons.
36 const DETECTOR_SNAPSHOT_PERIOD: isize = 256;
38 /// The `EvalContext` is only meant to be used to do field and index projections into constants for
39 /// `simd_shuffle` and const patterns in match arms.
41 /// The function containing the `match` that is currently being analyzed may have generic bounds
42 /// that inform us about the generic bounds of the constant. E.g., using an associated constant
43 /// of a function's generic parameter will require knowledge about the bounds on the generic
44 /// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
45 pub(crate) fn mk_eval_cx<'a, 'mir, 'tcx>(
46 tcx: TyCtxt<'a, 'tcx, 'tcx>,
48 param_env: ty::ParamEnv<'tcx>,
49 ) -> CompileTimeEvalContext<'a, 'mir, 'tcx> {
50 debug!("mk_eval_cx: {:?}", param_env);
51 EvalContext::new(tcx.at(span), param_env, CompileTimeInterpreter::new())
54 pub(crate) fn eval_promoted<'a, 'mir, 'tcx>(
55 tcx: TyCtxt<'a, 'tcx, 'tcx>,
57 mir: &'mir mir::Mir<'tcx>,
58 param_env: ty::ParamEnv<'tcx>,
59 ) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
60 let span = tcx.def_span(cid.instance.def_id());
61 let mut ecx = mk_eval_cx(tcx, span, param_env);
62 eval_body_using_ecx(&mut ecx, cid, Some(mir), param_env)
65 fn mplace_to_const<'tcx>(
66 ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
67 mplace: MPlaceTy<'tcx>,
68 ) -> EvalResult<'tcx, ty::Const<'tcx>> {
69 let MemPlace { ptr, align, meta } = *mplace;
70 // extract alloc-offset pair
71 assert!(meta.is_none());
72 let ptr = ptr.to_ptr()?;
73 let alloc = ecx.memory.get(ptr.alloc_id)?;
74 assert!(alloc.align >= align);
75 assert!(alloc.bytes.len() as u64 - ptr.offset.bytes() >= mplace.layout.size.bytes());
76 let mut alloc = alloc.clone();
78 // FIXME shouldn't it be the case that `mark_static_initialized` has already
79 // interned this? I thought that is the entire point of that `FinishStatic` stuff?
80 let alloc = ecx.tcx.intern_const_alloc(alloc);
81 let val = ConstValue::ByRef(ptr, alloc);
82 Ok(ty::Const { val, ty: mplace.layout.ty })
86 ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
88 ) -> EvalResult<'tcx, ty::Const<'tcx>> {
89 // We do not normalize just any data. Only scalar layout and slices.
90 let normalize = match op.layout.abi {
91 layout::Abi::Scalar(..) => true,
92 layout::Abi::ScalarPair(..) => op.layout.ty.is_slice(),
95 let normalized_op = if normalize {
96 Err(*ecx.read_immediate(op).expect("normalization works on validated constants"))
100 let val = match normalized_op {
101 Ok(mplace) => return mplace_to_const(ecx, mplace),
102 Err(Immediate::Scalar(x)) =>
103 ConstValue::Scalar(x.not_undef()?),
104 Err(Immediate::ScalarPair(a, b)) =>
105 ConstValue::Slice(a.not_undef()?, b.to_usize(ecx)?),
107 Ok(ty::Const { val, ty: op.layout.ty })
110 fn eval_body_and_ecx<'a, 'mir, 'tcx>(
111 tcx: TyCtxt<'a, 'tcx, 'tcx>,
113 mir: Option<&'mir mir::Mir<'tcx>>,
114 param_env: ty::ParamEnv<'tcx>,
115 ) -> (EvalResult<'tcx, MPlaceTy<'tcx>>, CompileTimeEvalContext<'a, 'mir, 'tcx>) {
116 // we start out with the best span we have
117 // and try improving it down the road when more information is available
118 let span = tcx.def_span(cid.instance.def_id());
119 let span = mir.map(|mir| mir.span).unwrap_or(span);
120 let mut ecx = EvalContext::new(tcx.at(span), param_env, CompileTimeInterpreter::new());
121 let r = eval_body_using_ecx(&mut ecx, cid, mir, param_env);
125 // Returns a pointer to where the result lives
126 fn eval_body_using_ecx<'mir, 'tcx>(
127 ecx: &mut CompileTimeEvalContext<'_, 'mir, 'tcx>,
129 mir: Option<&'mir mir::Mir<'tcx>>,
130 param_env: ty::ParamEnv<'tcx>,
131 ) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
132 debug!("eval_body_using_ecx: {:?}, {:?}", cid, param_env);
133 let tcx = ecx.tcx.tcx;
134 let mut mir = match mir {
136 None => ecx.load_mir(cid.instance.def)?,
138 if let Some(index) = cid.promoted {
139 mir = &mir.promoted[index];
141 let layout = ecx.layout_of(mir.return_ty().subst(tcx, cid.instance.substs))?;
142 assert!(!layout.is_unsized());
143 let ret = ecx.allocate(layout, MemoryKind::Stack);
145 let name = ty::tls::with(|tcx| tcx.item_path_str(cid.instance.def_id()));
146 let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
147 trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
148 assert!(mir.arg_count == 0);
149 ecx.push_stack_frame(
154 StackPopCleanup::None { cleanup: false },
157 // The main interpreter loop.
161 let internally_mutable = !layout.ty.is_freeze(tcx, param_env, mir.span);
162 let is_static = tcx.is_static(cid.instance.def_id());
163 let mutability = if is_static == Some(hir::Mutability::MutMutable) || internally_mutable {
166 Mutability::Immutable
168 ecx.memory.intern_static(ret.ptr.to_ptr()?.alloc_id, mutability)?;
170 debug!("eval_body_using_ecx done: {:?}", *ret);
174 impl<'tcx> Into<EvalError<'tcx>> for ConstEvalError {
175 fn into(self) -> EvalError<'tcx> {
176 EvalErrorKind::MachineError(self.to_string()).into()
180 #[derive(Clone, Debug)]
181 enum ConstEvalError {
185 impl fmt::Display for ConstEvalError {
186 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
187 use self::ConstEvalError::*;
189 NeedsRfc(ref msg) => {
192 "\"{}\" needs an rfc before being allowed inside constants",
200 impl Error for ConstEvalError {
201 fn description(&self) -> &str {
202 use self::ConstEvalError::*;
204 NeedsRfc(_) => "this feature needs an rfc before being allowed inside constants",
208 fn cause(&self) -> Option<&dyn Error> {
213 // Extra machine state for CTFE, and the Machine instance
214 pub struct CompileTimeInterpreter<'a, 'mir, 'tcx: 'a+'mir> {
215 /// When this value is negative, it indicates the number of interpreter
216 /// steps *until* the loop detector is enabled. When it is positive, it is
217 /// the number of steps after the detector has been enabled modulo the loop
219 pub(super) steps_since_detector_enabled: isize,
221 /// Extra state to detect loops.
222 pub(super) loop_detector: snapshot::InfiniteLoopDetector<'a, 'mir, 'tcx>,
225 impl<'a, 'mir, 'tcx> CompileTimeInterpreter<'a, 'mir, 'tcx> {
227 CompileTimeInterpreter {
228 loop_detector: Default::default(),
229 steps_since_detector_enabled: -STEPS_UNTIL_DETECTOR_ENABLED,
234 impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
236 fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
239 FxHashMap::contains_key(self, k)
243 fn insert(&mut self, k: K, v: V) -> Option<V>
245 FxHashMap::insert(self, k, v)
249 fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
252 FxHashMap::remove(self, k)
256 fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
258 .filter_map(move |(k, v)| f(k, &*v))
266 vacant: impl FnOnce() -> Result<V, E>
273 bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
282 vacant: impl FnOnce() -> Result<V, E>
283 ) -> Result<&mut V, E>
285 match self.entry(k) {
286 Entry::Occupied(e) => Ok(e.into_mut()),
287 Entry::Vacant(e) => {
295 type CompileTimeEvalContext<'a, 'mir, 'tcx> =
296 EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>;
298 impl interpret::MayLeak for ! {
300 fn may_leak(self) -> bool {
301 // `self` is uninhabited
306 impl<'a, 'mir, 'tcx> interpret::Machine<'a, 'mir, 'tcx>
307 for CompileTimeInterpreter<'a, 'mir, 'tcx>
309 type MemoryKinds = !;
310 type PointerTag = ();
312 type FrameExtra = ();
313 type MemoryExtra = ();
314 type AllocExtra = ();
316 type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
318 const STATIC_KIND: Option<!> = None; // no copying of statics allowed
321 fn enforce_validity(_ecx: &EvalContext<'a, 'mir, 'tcx, Self>) -> bool {
322 false // for now, we don't enforce validity
326 ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
327 instance: ty::Instance<'tcx>,
329 dest: Option<PlaceTy<'tcx>>,
330 ret: Option<mir::BasicBlock>,
331 ) -> EvalResult<'tcx, Option<&'mir mir::Mir<'tcx>>> {
332 debug!("eval_fn_call: {:?}", instance);
333 // Only check non-glue functions
334 if let ty::InstanceDef::Item(def_id) = instance.def {
335 // Execution might have wandered off into other crates, so we cannot to a stability-
336 // sensitive check here. But we can at least rule out functions that are not const
338 if !ecx.tcx.is_const_fn_raw(def_id) {
339 // Some functions we support even if they are non-const -- but avoid testing
340 // that for const fn! We certainly do *not* want to actually call the fn
341 // though, so be sure we return here.
342 return if ecx.hook_fn(instance, args, dest)? {
343 ecx.goto_block(ret)?; // fully evaluated and done
346 err!(MachineError(format!("calling non-const function `{}`", instance)))
350 // This is a const fn. Call it.
351 Ok(Some(match ecx.load_mir(instance.def) {
354 if let EvalErrorKind::NoMirFor(ref path) = err.kind {
356 ConstEvalError::NeedsRfc(format!("calling extern function `{}`", path))
366 ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
367 instance: ty::Instance<'tcx>,
370 ) -> EvalResult<'tcx> {
371 if ecx.emulate_intrinsic(instance, args, dest)? {
374 // An intrinsic that we do not support
375 let intrinsic_name = &ecx.tcx.item_name(instance.def_id()).as_str()[..];
377 ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into()
382 _ecx: &EvalContext<'a, 'mir, 'tcx, Self>,
386 ) -> EvalResult<'tcx, (Scalar, bool)> {
388 ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into(),
392 fn find_foreign_static(
394 _tcx: TyCtxtAt<'a, 'tcx, 'tcx>,
396 ) -> EvalResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> {
397 err!(ReadForeignStatic)
401 fn adjust_static_allocation<'b>(
402 alloc: &'b Allocation,
404 ) -> Cow<'b, Allocation<Self::PointerTag>> {
405 // We do not use a tag so we can just cheaply forward the reference
410 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
411 _dest: PlaceTy<'tcx>,
412 ) -> EvalResult<'tcx> {
414 ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into(),
418 fn before_terminator(ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>) -> EvalResult<'tcx> {
420 let steps = &mut ecx.machine.steps_since_detector_enabled;
427 *steps %= DETECTOR_SNAPSHOT_PERIOD;
433 let span = ecx.frame().span;
434 ecx.machine.loop_detector.observe_and_analyze(
443 fn tag_new_allocation(
444 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
446 _kind: MemoryKind<Self::MemoryKinds>,
453 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
454 ) -> EvalResult<'tcx> {
458 /// Called immediately before a stack frame gets popped.
461 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
463 ) -> EvalResult<'tcx> {
468 /// Projects to a field of a (variant of a) const.
469 pub fn const_field<'a, 'tcx>(
470 tcx: TyCtxt<'a, 'tcx, 'tcx>,
471 param_env: ty::ParamEnv<'tcx>,
472 variant: Option<VariantIdx>,
474 value: ty::Const<'tcx>,
475 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
476 trace!("const_field: {:?}, {:?}", field, value);
477 let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
479 // get the operand again
480 let op = ecx.const_to_op(value, None)?;
482 let down = match variant {
484 Some(variant) => ecx.operand_downcast(op, variant)?
487 let field = ecx.operand_field(down, field.index() as u64)?;
488 // and finally move back to the const world, always normalizing because
489 // this is not called for statics.
490 op_to_const(&ecx, field)
492 result.map_err(|error| {
493 let err = error_to_const_error(&ecx, error);
494 err.report_as_error(ecx.tcx, "could not access field of constant");
495 ErrorHandled::Reported
499 pub fn const_variant_index<'a, 'tcx>(
500 tcx: TyCtxt<'a, 'tcx, 'tcx>,
501 param_env: ty::ParamEnv<'tcx>,
502 val: ty::Const<'tcx>,
503 ) -> EvalResult<'tcx, VariantIdx> {
504 trace!("const_variant_index: {:?}", val);
505 let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
506 let op = ecx.const_to_op(val, None)?;
507 Ok(ecx.read_discriminant(op)?.1)
510 pub fn error_to_const_error<'a, 'mir, 'tcx>(
511 ecx: &EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>,
512 mut error: EvalError<'tcx>
513 ) -> ConstEvalErr<'tcx> {
514 error.print_backtrace();
515 let stacktrace = ecx.generate_stacktrace(None);
516 ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
519 fn validate_and_turn_into_const<'a, 'tcx>(
520 tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
521 constant: RawConst<'tcx>,
522 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
523 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
525 let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env);
527 let mplace = ecx.raw_const_to_mplace(constant)?;
528 let mut ref_tracking = RefTracking::new(mplace);
529 while let Some((mplace, path)) = ref_tracking.todo.pop() {
530 ecx.validate_operand(
533 Some(&mut ref_tracking),
537 // Now that we validated, turn this into a proper constant.
538 let def_id = cid.instance.def.def_id();
539 if tcx.is_static(def_id).is_some() || cid.promoted.is_some() {
540 mplace_to_const(&ecx, mplace)
542 op_to_const(&ecx, mplace.into())
546 val.map_err(|error| {
547 let err = error_to_const_error(&ecx, error);
548 match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
550 diag.note("The rules on what exactly is undefined behavior aren't clear, \
551 so this check might be overzealous. Please open an issue on the rust compiler \
552 repository if you believe it should not be considered undefined behavior",
555 ErrorHandled::Reported
562 pub fn const_eval_provider<'a, 'tcx>(
563 tcx: TyCtxt<'a, 'tcx, 'tcx>,
564 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
565 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
566 // see comment in const_eval_provider for what we're doing here
567 if key.param_env.reveal == Reveal::All {
568 let mut key = key.clone();
569 key.param_env.reveal = Reveal::UserFacing;
570 match tcx.const_eval(key) {
571 // try again with reveal all as requested
572 Err(ErrorHandled::TooGeneric) => {
573 // Promoteds should never be "too generic" when getting evaluated.
574 // They either don't get evaluated, or we are in a monomorphic context
575 assert!(key.value.promoted.is_none());
578 other => return other,
581 tcx.const_eval_raw(key).and_then(|val| {
582 validate_and_turn_into_const(tcx, val, key)
586 pub fn const_eval_raw_provider<'a, 'tcx>(
587 tcx: TyCtxt<'a, 'tcx, 'tcx>,
588 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
589 ) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
590 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
591 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
592 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
593 // computed. For a large percentage of constants that will already have succeeded. Only
594 // associated constants of generic functions will fail due to not enough monomorphization
595 // information being available.
597 // In case we fail in the `UserFacing` variant, we just do the real computation.
598 if key.param_env.reveal == Reveal::All {
599 let mut key = key.clone();
600 key.param_env.reveal = Reveal::UserFacing;
601 match tcx.const_eval_raw(key) {
602 // try again with reveal all as requested
603 Err(ErrorHandled::TooGeneric) => {},
605 other => return other,
608 // the first trace is for replicating an ice
609 // There's no tracking issue, but the next two lines concatenated link to the discussion on
610 // zulip. It's not really possible to test this, because it doesn't show up in diagnostics
612 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
613 // subject/anon_const_instance_printing/near/135980032
614 trace!("const eval: {}", key.value.instance);
615 trace!("const eval: {:?}", key);
618 let def_id = cid.instance.def.def_id();
620 if let Some(id) = tcx.hir().as_local_node_id(def_id) {
621 let tables = tcx.typeck_tables_of(def_id);
623 // Do match-check before building MIR
624 if let Err(ErrorReported) = tcx.check_match(def_id) {
625 return Err(ErrorHandled::Reported)
628 if let hir::BodyOwnerKind::Const = tcx.hir().body_owner_kind(id) {
629 tcx.mir_const_qualif(def_id);
632 // Do not continue into miri if typeck errors occurred; it will fail horribly
633 if tables.tainted_by_errors {
634 return Err(ErrorHandled::Reported)
638 let (res, ecx) = eval_body_and_ecx(tcx, cid, None, key.param_env);
639 res.and_then(|place| {
641 alloc_id: place.to_ptr().expect("we allocated this ptr!").alloc_id,
645 let err = error_to_const_error(&ecx, error);
646 // errors in statics are always emitted as fatal errors
647 if tcx.is_static(def_id).is_some() {
648 let reported_err = err.report_as_error(ecx.tcx,
649 "could not evaluate static initializer");
650 // Ensure that if the above error was either `TooGeneric` or `Reported`
651 // an error must be reported.
652 if tcx.sess.err_count() == 0 {
653 tcx.sess.delay_span_bug(err.span,
654 &format!("static eval failure did not emit an error: {:#?}",
658 } else if def_id.is_local() {
659 // constant defined in this crate, we can figure out a lint level!
660 match tcx.describe_def(def_id) {
661 // constants never produce a hard error at the definition site. Anything else is
662 // a backwards compatibility hazard (and will break old versions of winapi for sure)
664 // note that validation may still cause a hard error on this very same constant,
665 // because any code that existed before validation could not have failed validation
666 // thus preventing such a hard error from being a backwards compatibility hazard
667 Some(Def::Const(_)) | Some(Def::AssociatedConst(_)) => {
668 let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
670 tcx.at(tcx.def_span(def_id)),
671 "any use of this value will cause an error",
675 // promoting runtime code is only allowed to error if it references broken constants
676 // any other kind of error will be reported to the user as a deny-by-default lint
677 _ => if let Some(p) = cid.promoted {
678 let span = tcx.optimized_mir(def_id).promoted[p].span;
679 if let EvalErrorKind::ReferencedConstant = err.error {
682 "evaluation of constant expression failed",
687 "reaching this expression at runtime will panic or abort",
688 tcx.hir().as_local_node_id(def_id).unwrap(),
691 // anything else (array lengths, enum initializers, constant patterns) are reported
696 "evaluation of constant value failed",
701 // use of broken constant from other crate
702 err.report_as_error(ecx.tcx, "could not evaluate constant")