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;
19 use syntax::ast::Mutability;
20 use syntax::source_map::{Span, DUMMY_SP};
22 use crate::interpret::{self,
23 PlaceTy, MPlaceTy, MemPlace, OpTy, ImmTy, Immediate, Scalar, Pointer,
25 EvalResult, EvalError, EvalErrorKind, GlobalId, InterpretCx, StackPopCleanup,
26 Allocation, AllocId, MemoryKind,
27 snapshot, RefTracking,
30 /// Number of steps until the detector even starts doing anything.
31 /// Also, a warning is shown to the user when this number is reached.
32 const STEPS_UNTIL_DETECTOR_ENABLED: isize = 1_000_000;
33 /// The number of steps between loop detector snapshots.
34 /// Should be a power of two for performance reasons.
35 const DETECTOR_SNAPSHOT_PERIOD: isize = 256;
37 /// The `InterpretCx` is only meant to be used to do field and index projections into constants for
38 /// `simd_shuffle` and const patterns in match arms.
40 /// The function containing the `match` that is currently being analyzed may have generic bounds
41 /// that inform us about the generic bounds of the constant. E.g., using an associated constant
42 /// of a function's generic parameter will require knowledge about the bounds on the generic
43 /// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
44 pub(crate) fn mk_eval_cx<'a, 'mir, 'tcx>(
45 tcx: TyCtxt<'a, 'tcx, 'tcx>,
47 param_env: ty::ParamEnv<'tcx>,
48 ) -> CompileTimeEvalContext<'a, 'mir, 'tcx> {
49 debug!("mk_eval_cx: {:?}", param_env);
50 InterpretCx::new(tcx.at(span), param_env, CompileTimeInterpreter::new())
53 pub(crate) fn eval_promoted<'a, 'mir, 'tcx>(
54 tcx: TyCtxt<'a, 'tcx, 'tcx>,
56 mir: &'mir mir::Mir<'tcx>,
57 param_env: ty::ParamEnv<'tcx>,
58 ) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
59 let span = tcx.def_span(cid.instance.def_id());
60 let mut ecx = mk_eval_cx(tcx, span, param_env);
61 eval_body_using_ecx(&mut ecx, cid, Some(mir), param_env)
64 fn mplace_to_const<'tcx>(
65 ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
66 mplace: MPlaceTy<'tcx>,
67 ) -> ty::Const<'tcx> {
68 let MemPlace { ptr, align, meta } = *mplace;
69 // extract alloc-offset pair
70 assert!(meta.is_none());
71 let ptr = ptr.to_ptr().unwrap();
72 let alloc = ecx.memory.get(ptr.alloc_id).unwrap();
73 assert!(alloc.align >= align);
74 assert!(alloc.bytes.len() as u64 - ptr.offset.bytes() >= mplace.layout.size.bytes());
75 let mut alloc = alloc.clone();
77 // FIXME shouldn't it be the case that `mark_static_initialized` has already
78 // interned this? I thought that is the entire point of that `FinishStatic` stuff?
79 let alloc = ecx.tcx.intern_const_alloc(alloc);
80 let val = ConstValue::ByRef(ptr, alloc);
81 ty::Const { val, ty: mplace.layout.ty }
85 ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
87 ) -> ty::Const<'tcx> {
88 // We do not normalize just any data. Only non-union scalars and slices.
89 let normalize = match op.layout.abi {
90 layout::Abi::Scalar(..) => op.layout.ty.ty_adt_def().map_or(true, |adt| !adt.is_union()),
91 layout::Abi::ScalarPair(..) => op.layout.ty.is_slice(),
94 let normalized_op = if normalize {
95 Err(*ecx.read_immediate(op).expect("normalization works on validated constants"))
99 let val = match normalized_op {
100 Ok(mplace) => return mplace_to_const(ecx, mplace),
101 Err(Immediate::Scalar(x)) =>
102 ConstValue::Scalar(x.not_undef().unwrap()),
103 Err(Immediate::ScalarPair(a, b)) =>
104 ConstValue::Slice(a.not_undef().unwrap(), b.to_usize(ecx).unwrap()),
106 ty::Const { val, ty: op.layout.ty }
109 fn eval_body_and_ecx<'a, 'mir, 'tcx>(
110 tcx: TyCtxt<'a, 'tcx, 'tcx>,
112 mir: Option<&'mir mir::Mir<'tcx>>,
113 param_env: ty::ParamEnv<'tcx>,
114 ) -> (EvalResult<'tcx, MPlaceTy<'tcx>>, CompileTimeEvalContext<'a, 'mir, 'tcx>) {
115 // we start out with the best span we have
116 // and try improving it down the road when more information is available
117 let span = tcx.def_span(cid.instance.def_id());
118 let span = mir.map(|mir| mir.span).unwrap_or(span);
119 let mut ecx = InterpretCx::new(tcx.at(span), param_env, CompileTimeInterpreter::new());
120 let r = eval_body_using_ecx(&mut ecx, cid, mir, param_env);
124 // Returns a pointer to where the result lives
125 fn eval_body_using_ecx<'mir, 'tcx>(
126 ecx: &mut CompileTimeEvalContext<'_, 'mir, 'tcx>,
128 mir: Option<&'mir mir::Mir<'tcx>>,
129 param_env: ty::ParamEnv<'tcx>,
130 ) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
131 debug!("eval_body_using_ecx: {:?}, {:?}", cid, param_env);
132 let tcx = ecx.tcx.tcx;
133 let mut mir = match mir {
135 None => ecx.load_mir(cid.instance.def)?,
137 if let Some(index) = cid.promoted {
138 mir = &mir.promoted[index];
140 let layout = ecx.layout_of(mir.return_ty().subst(tcx, cid.instance.substs))?;
141 assert!(!layout.is_unsized());
142 let ret = ecx.allocate(layout, MemoryKind::Stack);
144 let name = ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id()));
145 let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
146 trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
147 assert!(mir.arg_count == 0);
148 ecx.push_stack_frame(
153 StackPopCleanup::None { cleanup: false },
156 // The main interpreter loop.
160 let internally_mutable = !layout.ty.is_freeze(tcx, param_env, mir.span);
161 let is_static = tcx.is_static(cid.instance.def_id());
162 let mutability = if is_static == Some(hir::Mutability::MutMutable) || internally_mutable {
165 Mutability::Immutable
167 ecx.memory.intern_static(ret.ptr.to_ptr()?.alloc_id, mutability)?;
169 debug!("eval_body_using_ecx done: {:?}", *ret);
173 impl<'tcx> Into<EvalError<'tcx>> for ConstEvalError {
174 fn into(self) -> EvalError<'tcx> {
175 EvalErrorKind::MachineError(self.to_string()).into()
179 #[derive(Clone, Debug)]
180 enum ConstEvalError {
184 impl fmt::Display for ConstEvalError {
185 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
186 use self::ConstEvalError::*;
188 NeedsRfc(ref msg) => {
191 "\"{}\" needs an rfc before being allowed inside constants",
199 impl Error for ConstEvalError {
200 fn description(&self) -> &str {
201 use self::ConstEvalError::*;
203 NeedsRfc(_) => "this feature needs an rfc before being allowed inside constants",
207 fn cause(&self) -> Option<&dyn Error> {
212 // Extra machine state for CTFE, and the Machine instance
213 pub struct CompileTimeInterpreter<'a, 'mir, 'tcx: 'a+'mir> {
214 /// When this value is negative, it indicates the number of interpreter
215 /// steps *until* the loop detector is enabled. When it is positive, it is
216 /// the number of steps after the detector has been enabled modulo the loop
218 pub(super) steps_since_detector_enabled: isize,
220 /// Extra state to detect loops.
221 pub(super) loop_detector: snapshot::InfiniteLoopDetector<'a, 'mir, 'tcx>,
224 impl<'a, 'mir, 'tcx> CompileTimeInterpreter<'a, 'mir, 'tcx> {
226 CompileTimeInterpreter {
227 loop_detector: Default::default(),
228 steps_since_detector_enabled: -STEPS_UNTIL_DETECTOR_ENABLED,
233 impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
235 fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
238 FxHashMap::contains_key(self, k)
242 fn insert(&mut self, k: K, v: V) -> Option<V>
244 FxHashMap::insert(self, k, v)
248 fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
251 FxHashMap::remove(self, k)
255 fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
257 .filter_map(move |(k, v)| f(k, &*v))
265 vacant: impl FnOnce() -> Result<V, E>
272 bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
281 vacant: impl FnOnce() -> Result<V, E>
282 ) -> Result<&mut V, E>
284 match self.entry(k) {
285 Entry::Occupied(e) => Ok(e.into_mut()),
286 Entry::Vacant(e) => {
294 type CompileTimeEvalContext<'a, 'mir, 'tcx> =
295 InterpretCx<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>;
297 impl interpret::MayLeak for ! {
299 fn may_leak(self) -> bool {
300 // `self` is uninhabited
305 impl<'a, 'mir, 'tcx> interpret::Machine<'a, 'mir, 'tcx>
306 for CompileTimeInterpreter<'a, 'mir, 'tcx>
308 type MemoryKinds = !;
309 type PointerTag = ();
311 type FrameExtra = ();
312 type MemoryExtra = ();
313 type AllocExtra = ();
315 type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
317 const STATIC_KIND: Option<!> = None; // no copying of statics allowed
320 fn enforce_validity(_ecx: &InterpretCx<'a, 'mir, 'tcx, Self>) -> bool {
321 false // for now, we don't enforce validity
325 ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>,
326 instance: ty::Instance<'tcx>,
328 dest: Option<PlaceTy<'tcx>>,
329 ret: Option<mir::BasicBlock>,
330 ) -> EvalResult<'tcx, Option<&'mir mir::Mir<'tcx>>> {
331 debug!("eval_fn_call: {:?}", instance);
332 // Only check non-glue functions
333 if let ty::InstanceDef::Item(def_id) = instance.def {
334 // Execution might have wandered off into other crates, so we cannot to a stability-
335 // sensitive check here. But we can at least rule out functions that are not const
337 if !ecx.tcx.is_const_fn_raw(def_id) {
338 // Some functions we support even if they are non-const -- but avoid testing
339 // that for const fn! We certainly do *not* want to actually call the fn
340 // though, so be sure we return here.
341 return if ecx.hook_fn(instance, args, dest)? {
342 ecx.goto_block(ret)?; // fully evaluated and done
345 err!(MachineError(format!("calling non-const function `{}`", instance)))
349 // This is a const fn. Call it.
350 Ok(Some(match ecx.load_mir(instance.def) {
353 if let EvalErrorKind::NoMirFor(ref path) = err.kind {
355 ConstEvalError::NeedsRfc(format!("calling extern function `{}`", path))
365 ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>,
366 instance: ty::Instance<'tcx>,
369 ) -> EvalResult<'tcx> {
370 if ecx.emulate_intrinsic(instance, args, dest)? {
373 // An intrinsic that we do not support
374 let intrinsic_name = &ecx.tcx.item_name(instance.def_id()).as_str()[..];
376 ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into()
381 _ecx: &InterpretCx<'a, 'mir, 'tcx, Self>,
385 ) -> EvalResult<'tcx, (Scalar, bool)> {
387 ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into(),
391 fn find_foreign_static(
393 _tcx: TyCtxtAt<'a, 'tcx, 'tcx>,
395 ) -> EvalResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> {
396 err!(ReadForeignStatic)
400 fn adjust_static_allocation<'b>(
401 alloc: &'b Allocation,
403 ) -> Cow<'b, Allocation<Self::PointerTag>> {
404 // We do not use a tag so we can just cheaply forward the reference
409 _ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>,
410 _dest: PlaceTy<'tcx>,
411 ) -> EvalResult<'tcx> {
413 ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into(),
417 fn before_terminator(ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>) -> EvalResult<'tcx> {
419 let steps = &mut ecx.machine.steps_since_detector_enabled;
426 *steps %= DETECTOR_SNAPSHOT_PERIOD;
432 let span = ecx.frame().span;
433 ecx.machine.loop_detector.observe_and_analyze(
442 fn tag_new_allocation(
443 _ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>,
445 _kind: MemoryKind<Self::MemoryKinds>,
452 _ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>,
453 ) -> EvalResult<'tcx> {
457 /// Called immediately before a stack frame gets popped.
460 _ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>,
462 ) -> EvalResult<'tcx> {
467 /// Projects to a field of a (variant of a) const.
468 // this function uses `unwrap` copiously, because an already validated constant must have valid
469 // fields and can thus never fail outside of compiler bugs
470 pub fn const_field<'a, 'tcx>(
471 tcx: TyCtxt<'a, 'tcx, 'tcx>,
472 param_env: ty::ParamEnv<'tcx>,
473 variant: Option<VariantIdx>,
475 value: ty::Const<'tcx>,
476 ) -> ty::Const<'tcx> {
477 trace!("const_field: {:?}, {:?}", field, value);
478 let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
479 // get the operand again
480 let op = ecx.eval_const_to_op(value, None).unwrap();
482 let down = match variant {
484 Some(variant) => ecx.operand_downcast(op, variant).unwrap(),
487 let field = ecx.operand_field(down, field.index() as u64).unwrap();
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)
493 // this function uses `unwrap` copiously, because an already validated constant must have valid
494 // fields and can thus never fail outside of compiler bugs
495 pub fn const_variant_index<'a, 'tcx>(
496 tcx: TyCtxt<'a, 'tcx, 'tcx>,
497 param_env: ty::ParamEnv<'tcx>,
498 val: ty::Const<'tcx>,
500 trace!("const_variant_index: {:?}", val);
501 let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
502 let op = ecx.eval_const_to_op(val, None).unwrap();
503 ecx.read_discriminant(op).unwrap().1
506 pub fn error_to_const_error<'a, 'mir, 'tcx>(
507 ecx: &InterpretCx<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>,
508 mut error: EvalError<'tcx>
509 ) -> ConstEvalErr<'tcx> {
510 error.print_backtrace();
511 let stacktrace = ecx.generate_stacktrace(None);
512 ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
515 fn validate_and_turn_into_const<'a, 'tcx>(
516 tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
517 constant: RawConst<'tcx>,
518 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
519 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
521 let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env);
523 let mplace = ecx.raw_const_to_mplace(constant)?;
524 let mut ref_tracking = RefTracking::new(mplace);
525 while let Some((mplace, path)) = ref_tracking.todo.pop() {
526 ecx.validate_operand(
529 Some(&mut ref_tracking),
533 // Now that we validated, turn this into a proper constant.
534 let def_id = cid.instance.def.def_id();
535 if tcx.is_static(def_id).is_some() || cid.promoted.is_some() {
536 Ok(mplace_to_const(&ecx, mplace))
538 Ok(op_to_const(&ecx, mplace.into()))
542 val.map_err(|error| {
543 let err = error_to_const_error(&ecx, error);
544 match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
546 diag.note("The rules on what exactly is undefined behavior aren't clear, \
547 so this check might be overzealous. Please open an issue on the rust compiler \
548 repository if you believe it should not be considered undefined behavior",
551 ErrorHandled::Reported
558 pub fn const_eval_provider<'a, 'tcx>(
559 tcx: TyCtxt<'a, 'tcx, 'tcx>,
560 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
561 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
562 // see comment in const_eval_provider for what we're doing here
563 if key.param_env.reveal == Reveal::All {
564 let mut key = key.clone();
565 key.param_env.reveal = Reveal::UserFacing;
566 match tcx.const_eval(key) {
567 // try again with reveal all as requested
568 Err(ErrorHandled::TooGeneric) => {
569 // Promoteds should never be "too generic" when getting evaluated.
570 // They either don't get evaluated, or we are in a monomorphic context
571 assert!(key.value.promoted.is_none());
574 other => return other,
577 tcx.const_eval_raw(key).and_then(|val| {
578 validate_and_turn_into_const(tcx, val, key)
582 pub fn const_eval_raw_provider<'a, 'tcx>(
583 tcx: TyCtxt<'a, 'tcx, 'tcx>,
584 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
585 ) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
586 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
587 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
588 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
589 // computed. For a large percentage of constants that will already have succeeded. Only
590 // associated constants of generic functions will fail due to not enough monomorphization
591 // information being available.
593 // In case we fail in the `UserFacing` variant, we just do the real computation.
594 if key.param_env.reveal == Reveal::All {
595 let mut key = key.clone();
596 key.param_env.reveal = Reveal::UserFacing;
597 match tcx.const_eval_raw(key) {
598 // try again with reveal all as requested
599 Err(ErrorHandled::TooGeneric) => {},
601 other => return other,
604 if cfg!(debug_assertions) {
605 // Make sure we format the instance even if we do not print it.
606 // This serves as a regression test against an ICE on printing.
607 // The next two lines concatenated contain some discussion:
608 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
609 // subject/anon_const_instance_printing/near/135980032
610 let instance = key.value.instance.to_string();
611 trace!("const eval: {:?} ({})", key, instance);
615 let def_id = cid.instance.def.def_id();
617 if let Some(id) = tcx.hir().as_local_hir_id(def_id) {
618 let tables = tcx.typeck_tables_of(def_id);
620 // Do match-check before building MIR
621 // FIXME(#59378) check_match may have errored but we're not checking for that anymore
622 tcx.check_match(def_id);
624 if let hir::BodyOwnerKind::Const = tcx.hir().body_owner_kind_by_hir_id(id) {
625 tcx.mir_const_qualif(def_id);
628 // Do not continue into miri if typeck errors occurred; it will fail horribly
629 if tables.tainted_by_errors {
630 return Err(ErrorHandled::Reported)
634 let (res, ecx) = eval_body_and_ecx(tcx, cid, None, key.param_env);
635 res.and_then(|place| {
637 alloc_id: place.to_ptr().expect("we allocated this ptr!").alloc_id,
641 let err = error_to_const_error(&ecx, error);
642 // errors in statics are always emitted as fatal errors
643 if tcx.is_static(def_id).is_some() {
644 let reported_err = err.report_as_error(ecx.tcx,
645 "could not evaluate static initializer");
646 // Ensure that if the above error was either `TooGeneric` or `Reported`
647 // an error must be reported.
648 let errs = tcx.sess.track_errors(|| {
649 tcx.sess.err_count();
652 Ok(_) => tcx.sess.delay_span_bug(err.span,
653 &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 hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
670 tcx.at(tcx.def_span(def_id)),
671 "any use of this value will cause an error",
676 // promoting runtime code is only allowed to error if it references broken constants
677 // any other kind of error will be reported to the user as a deny-by-default lint
678 _ => if let Some(p) = cid.promoted {
679 let span = tcx.optimized_mir(def_id).promoted[p].span;
680 if let EvalErrorKind::ReferencedConstant = err.error {
683 "evaluation of constant expression failed",
688 "reaching this expression at runtime will panic or abort",
689 tcx.hir().as_local_hir_id(def_id).unwrap(),
693 // anything else (array lengths, enum initializers, constant patterns) are reported
698 "evaluation of constant value failed",
703 // use of broken constant from other crate
704 err.report_as_error(ecx.tcx, "could not evaluate constant")