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;
8 use std::convert::TryInto;
10 use rustc::hir::def::DefKind;
11 use rustc::hir::def_id::DefId;
12 use rustc::mir::interpret::{ConstEvalErr, ErrorHandled, ScalarMaybeUndef};
14 use rustc::ty::{self, TyCtxt, query::TyCtxtAt};
15 use rustc::ty::layout::{self, LayoutOf, VariantIdx};
16 use rustc::ty::subst::Subst;
17 use rustc::traits::Reveal;
18 use rustc::util::common::ErrorReported;
19 use rustc_data_structures::fx::FxHashMap;
21 use syntax::source_map::{Span, DUMMY_SP};
23 use crate::interpret::{self,
24 PlaceTy, MPlaceTy, OpTy, ImmTy, Immediate, Scalar,
26 InterpResult, InterpErrorInfo, InterpError, GlobalId, InterpretCx, StackPopCleanup,
27 Allocation, AllocId, MemoryKind, Memory,
28 snapshot, RefTracking, intern_const_alloc_recursive,
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 `InterpretCx` 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<'mir, 'tcx>(
48 param_env: ty::ParamEnv<'tcx>,
49 ) -> CompileTimeEvalContext<'mir, 'tcx> {
50 debug!("mk_eval_cx: {:?}", param_env);
51 InterpretCx::new(tcx.at(span), param_env, CompileTimeInterpreter::new())
54 pub(crate) fn eval_promoted<'mir, 'tcx>(
57 body: &'mir mir::Body<'tcx>,
58 param_env: ty::ParamEnv<'tcx>,
59 ) -> InterpResult<'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, body, param_env)
66 ecx: &CompileTimeEvalContext<'_, 'tcx>,
68 ) -> &'tcx ty::Const<'tcx> {
69 // We do not have value optmizations for everything.
70 // Only scalars and slices, since they are very common.
71 // Note that further down we turn scalars of undefined bits back to `ByRef`. These can result
72 // from scalar unions that are initialized with one of their zero sized variants. We could
73 // instead allow `ConstValue::Scalar` to store `ScalarMaybeUndef`, but that would affect all
74 // the usual cases of extracting e.g. a `usize`, without there being a real use case for the
76 let try_as_immediate = match op.layout.abi {
77 layout::Abi::Scalar(..) => true,
78 layout::Abi::ScalarPair(..) => match op.layout.ty.sty {
79 ty::Ref(_, inner, _) => match inner.sty {
80 ty::Slice(elem) => elem == ecx.tcx.types.u8,
88 let immediate = if try_as_immediate {
89 Err(ecx.read_immediate(op).expect("normalization works on validated constants"))
91 // It is guaranteed that any non-slice scalar pair is actually ByRef here.
92 // When we come back from raw const eval, we are always by-ref. The only way our op here is
93 // by-val is if we are in const_field, i.e., if this is (a field of) something that we
94 // "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
95 // structs containing such.
98 let val = match immediate {
100 let ptr = mplace.ptr.to_ptr().unwrap();
101 let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
102 ConstValue::ByRef { offset: ptr.offset, align: mplace.align, alloc }
104 // see comment on `let try_as_immediate` above
105 Err(ImmTy { imm: Immediate::Scalar(x), .. }) => match x {
106 ScalarMaybeUndef::Scalar(s) => ConstValue::Scalar(s),
107 ScalarMaybeUndef::Undef => {
108 // When coming out of "normal CTFE", we'll always have an `Indirect` operand as
109 // argument and we will not need this. The only way we can already have an
110 // `Immediate` is when we are called from `const_field`, and that `Immediate`
111 // comes from a constant so it can happen have `Undef`, because the indirect
112 // memory that was read had undefined bytes.
113 let mplace = op.to_mem_place();
114 let ptr = mplace.ptr.to_ptr().unwrap();
115 let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
116 ConstValue::ByRef { offset: ptr.offset, align: mplace.align, alloc }
119 Err(ImmTy { imm: Immediate::ScalarPair(a, b), .. }) => {
120 let (data, start) = match a.not_undef().unwrap() {
121 Scalar::Ptr(ptr) => (
122 ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id),
125 Scalar::Raw { .. } => (
126 ecx.tcx.intern_const_alloc(Allocation::from_byte_aligned_bytes(
132 let len = b.to_usize(&ecx.tcx.tcx).unwrap();
133 let start = start.try_into().unwrap();
134 let len: usize = len.try_into().unwrap();
142 ecx.tcx.mk_const(ty::Const { val, ty: op.layout.ty })
145 // Returns a pointer to where the result lives
146 fn eval_body_using_ecx<'mir, 'tcx>(
147 ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
149 body: &'mir mir::Body<'tcx>,
150 param_env: ty::ParamEnv<'tcx>,
151 ) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
152 debug!("eval_body_using_ecx: {:?}, {:?}", cid, param_env);
153 let tcx = ecx.tcx.tcx;
154 let layout = ecx.layout_of(body.return_ty().subst(tcx, cid.instance.substs))?;
155 assert!(!layout.is_unsized());
156 let ret = ecx.allocate(layout, MemoryKind::Stack);
158 let name = ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id()));
159 let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
160 trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
161 assert!(body.arg_count == 0);
162 ecx.push_stack_frame(
167 StackPopCleanup::None { cleanup: false },
170 // The main interpreter loop.
174 intern_const_alloc_recursive(
176 cid.instance.def_id(),
181 debug!("eval_body_using_ecx done: {:?}", *ret);
185 impl<'tcx> Into<InterpErrorInfo<'tcx>> for ConstEvalError {
186 fn into(self) -> InterpErrorInfo<'tcx> {
187 InterpError::MachineError(self.to_string()).into()
191 #[derive(Clone, Debug)]
192 enum ConstEvalError {
196 impl fmt::Display for ConstEvalError {
197 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
198 use self::ConstEvalError::*;
200 NeedsRfc(ref msg) => {
203 "\"{}\" needs an rfc before being allowed inside constants",
211 impl Error for ConstEvalError {
212 fn description(&self) -> &str {
213 use self::ConstEvalError::*;
215 NeedsRfc(_) => "this feature needs an rfc before being allowed inside constants",
219 fn cause(&self) -> Option<&dyn Error> {
224 // Extra machine state for CTFE, and the Machine instance
225 pub struct CompileTimeInterpreter<'mir, 'tcx> {
226 /// When this value is negative, it indicates the number of interpreter
227 /// steps *until* the loop detector is enabled. When it is positive, it is
228 /// the number of steps after the detector has been enabled modulo the loop
230 pub(super) steps_since_detector_enabled: isize,
232 /// Extra state to detect loops.
233 pub(super) loop_detector: snapshot::InfiniteLoopDetector<'mir, 'tcx>,
236 impl<'mir, 'tcx> CompileTimeInterpreter<'mir, 'tcx> {
238 CompileTimeInterpreter {
239 loop_detector: Default::default(),
240 steps_since_detector_enabled: -STEPS_UNTIL_DETECTOR_ENABLED,
245 impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
247 fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
250 FxHashMap::contains_key(self, k)
254 fn insert(&mut self, k: K, v: V) -> Option<V>
256 FxHashMap::insert(self, k, v)
260 fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
263 FxHashMap::remove(self, k)
267 fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
269 .filter_map(move |(k, v)| f(k, &*v))
277 vacant: impl FnOnce() -> Result<V, E>
284 bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
293 vacant: impl FnOnce() -> Result<V, E>
294 ) -> Result<&mut V, E>
296 match self.entry(k) {
297 Entry::Occupied(e) => Ok(e.into_mut()),
298 Entry::Vacant(e) => {
306 crate type CompileTimeEvalContext<'mir, 'tcx> =
307 InterpretCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>;
309 impl interpret::MayLeak for ! {
311 fn may_leak(self) -> bool {
312 // `self` is uninhabited
317 impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir, 'tcx> {
318 type MemoryKinds = !;
319 type PointerTag = ();
321 type FrameExtra = ();
322 type MemoryExtra = ();
323 type AllocExtra = ();
325 type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
327 const STATIC_KIND: Option<!> = None; // no copying of statics allowed
330 fn enforce_validity(_ecx: &InterpretCx<'mir, 'tcx, Self>) -> bool {
331 false // for now, we don't enforce validity
335 ecx: &mut InterpretCx<'mir, 'tcx, Self>,
336 instance: ty::Instance<'tcx>,
338 dest: Option<PlaceTy<'tcx>>,
339 ret: Option<mir::BasicBlock>,
340 ) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>> {
341 debug!("eval_fn_call: {:?}", instance);
342 // Only check non-glue functions
343 if let ty::InstanceDef::Item(def_id) = instance.def {
344 // Execution might have wandered off into other crates, so we cannot to a stability-
345 // sensitive check here. But we can at least rule out functions that are not const
347 if !ecx.tcx.is_const_fn_raw(def_id) {
348 // Some functions we support even if they are non-const -- but avoid testing
349 // that for const fn! We certainly do *not* want to actually call the fn
350 // though, so be sure we return here.
351 return if ecx.hook_fn(instance, args, dest)? {
352 ecx.goto_block(ret)?; // fully evaluated and done
355 err!(MachineError(format!("calling non-const function `{}`", instance)))
359 // This is a const fn. Call it.
360 Ok(Some(match ecx.load_mir(instance.def) {
363 if let InterpError::NoMirFor(ref path) = err.kind {
365 ConstEvalError::NeedsRfc(format!("calling extern function `{}`", path))
375 ecx: &mut InterpretCx<'mir, 'tcx, Self>,
376 instance: ty::Instance<'tcx>,
379 ) -> InterpResult<'tcx> {
380 if ecx.emulate_intrinsic(instance, args, dest)? {
383 // An intrinsic that we do not support
384 let intrinsic_name = &ecx.tcx.item_name(instance.def_id()).as_str()[..];
386 ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into()
391 _ecx: &InterpretCx<'mir, 'tcx, Self>,
395 ) -> InterpResult<'tcx, (Scalar, bool)> {
397 ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into(),
401 fn find_foreign_static(
403 _tcx: TyCtxtAt<'tcx>,
404 ) -> InterpResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> {
405 err!(ReadForeignStatic)
409 fn tag_allocation<'b>(
411 alloc: Cow<'b, Allocation>,
412 _kind: Option<MemoryKind<!>>,
413 _memory: &Memory<'mir, 'tcx, Self>,
414 ) -> (Cow<'b, Allocation<Self::PointerTag>>, Self::PointerTag) {
415 // We do not use a tag so we can just cheaply forward the allocation
420 fn tag_static_base_pointer(
422 _memory: &Memory<'mir, 'tcx, Self>,
423 ) -> Self::PointerTag {
428 _ecx: &mut InterpretCx<'mir, 'tcx, Self>,
429 _dest: PlaceTy<'tcx>,
430 ) -> InterpResult<'tcx> {
432 ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into(),
436 fn before_terminator(ecx: &mut InterpretCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
438 let steps = &mut ecx.machine.steps_since_detector_enabled;
445 *steps %= DETECTOR_SNAPSHOT_PERIOD;
451 let span = ecx.frame().span;
452 ecx.machine.loop_detector.observe_and_analyze(
461 fn stack_push(_ecx: &mut InterpretCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
465 /// Called immediately before a stack frame gets popped.
467 fn stack_pop(_ecx: &mut InterpretCx<'mir, 'tcx, Self>, _extra: ()) -> InterpResult<'tcx> {
472 /// Extracts a field of a (variant of a) const.
473 // this function uses `unwrap` copiously, because an already validated constant must have valid
474 // fields and can thus never fail outside of compiler bugs
475 pub fn const_field<'tcx>(
477 param_env: ty::ParamEnv<'tcx>,
478 variant: Option<VariantIdx>,
480 value: &'tcx ty::Const<'tcx>,
481 ) -> &'tcx ty::Const<'tcx> {
482 trace!("const_field: {:?}, {:?}", field, value);
483 let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
484 // get the operand again
485 let op = ecx.eval_const_to_op(value, None).unwrap();
487 let down = match variant {
489 Some(variant) => ecx.operand_downcast(op, variant).unwrap(),
492 let field = ecx.operand_field(down, field.index() as u64).unwrap();
493 // and finally move back to the const world, always normalizing because
494 // this is not called for statics.
495 op_to_const(&ecx, field)
498 // this function uses `unwrap` copiously, because an already validated constant must have valid
499 // fields and can thus never fail outside of compiler bugs
500 pub fn const_variant_index<'tcx>(
502 param_env: ty::ParamEnv<'tcx>,
503 val: &'tcx ty::Const<'tcx>,
505 trace!("const_variant_index: {:?}", val);
506 let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
507 let op = ecx.eval_const_to_op(val, None).unwrap();
508 ecx.read_discriminant(op).unwrap().1
511 pub fn error_to_const_error<'mir, 'tcx>(
512 ecx: &InterpretCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
513 mut error: InterpErrorInfo<'tcx>,
514 ) -> ConstEvalErr<'tcx> {
515 error.print_backtrace();
516 let stacktrace = ecx.generate_stacktrace(None);
517 ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
520 fn validate_and_turn_into_const<'tcx>(
522 constant: RawConst<'tcx>,
523 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
524 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
526 let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env);
528 let mplace = ecx.raw_const_to_mplace(constant)?;
529 let mut ref_tracking = RefTracking::new(mplace);
530 while let Some((mplace, path)) = ref_tracking.todo.pop() {
531 ecx.validate_operand(
534 Some(&mut ref_tracking),
537 // Now that we validated, turn this into a proper constant.
538 // Statics/promoteds are always `ByRef`, for the rest `op_to_const` decides
539 // whether they become immediates.
540 let def_id = cid.instance.def.def_id();
541 if tcx.is_static(def_id) || cid.promoted.is_some() {
542 let ptr = mplace.ptr.to_ptr()?;
543 Ok(tcx.mk_const(ty::Const {
544 val: ConstValue::ByRef {
547 alloc: ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id),
549 ty: mplace.layout.ty,
552 Ok(op_to_const(&ecx, mplace.into()))
556 val.map_err(|error| {
557 let err = error_to_const_error(&ecx, error);
558 match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
560 diag.note("The rules on what exactly is undefined behavior aren't clear, \
561 so this check might be overzealous. Please open an issue on the rust compiler \
562 repository if you believe it should not be considered undefined behavior",
565 ErrorHandled::Reported
572 pub fn const_eval_provider<'tcx>(
574 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
575 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
576 // see comment in const_eval_provider for what we're doing here
577 if key.param_env.reveal == Reveal::All {
578 let mut key = key.clone();
579 key.param_env.reveal = Reveal::UserFacing;
580 match tcx.const_eval(key) {
581 // try again with reveal all as requested
582 Err(ErrorHandled::TooGeneric) => {
583 // Promoteds should never be "too generic" when getting evaluated.
584 // They either don't get evaluated, or we are in a monomorphic context
585 assert!(key.value.promoted.is_none());
588 other => return other,
591 tcx.const_eval_raw(key).and_then(|val| {
592 validate_and_turn_into_const(tcx, val, key)
596 pub fn const_eval_raw_provider<'tcx>(
598 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
599 ) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
600 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
601 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
602 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
603 // computed. For a large percentage of constants that will already have succeeded. Only
604 // associated constants of generic functions will fail due to not enough monomorphization
605 // information being available.
607 // In case we fail in the `UserFacing` variant, we just do the real computation.
608 if key.param_env.reveal == Reveal::All {
609 let mut key = key.clone();
610 key.param_env.reveal = Reveal::UserFacing;
611 match tcx.const_eval_raw(key) {
612 // try again with reveal all as requested
613 Err(ErrorHandled::TooGeneric) => {},
615 other => return other,
618 if cfg!(debug_assertions) {
619 // Make sure we format the instance even if we do not print it.
620 // This serves as a regression test against an ICE on printing.
621 // The next two lines concatenated contain some discussion:
622 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
623 // subject/anon_const_instance_printing/near/135980032
624 let instance = key.value.instance.to_string();
625 trace!("const eval: {:?} ({})", key, instance);
629 let def_id = cid.instance.def.def_id();
631 if def_id.is_local() && tcx.typeck_tables_of(def_id).tainted_by_errors {
632 return Err(ErrorHandled::Reported);
635 let span = tcx.def_span(cid.instance.def_id());
636 let mut ecx = InterpretCx::new(tcx.at(span), key.param_env, CompileTimeInterpreter::new());
638 let res = ecx.load_mir(cid.instance.def);
640 if let Some(index) = cid.promoted {
641 &body.promoted[index]
646 |body| eval_body_using_ecx(&mut ecx, cid, body, key.param_env)
649 alloc_id: place.to_ptr().expect("we allocated this ptr!").alloc_id,
653 let err = error_to_const_error(&ecx, error);
654 // errors in statics are always emitted as fatal errors
655 if tcx.is_static(def_id) {
656 // Ensure that if the above error was either `TooGeneric` or `Reported`
657 // an error must be reported.
658 let reported_err = tcx.sess.track_errors(|| {
659 err.report_as_error(ecx.tcx,
660 "could not evaluate static initializer")
664 tcx.sess.delay_span_bug(err.span,
665 &format!("static eval failure did not emit an error: {:#?}",
669 Err(ErrorReported) => ErrorHandled::Reported,
671 } else if def_id.is_local() {
672 // constant defined in this crate, we can figure out a lint level!
673 match tcx.def_kind(def_id) {
674 // constants never produce a hard error at the definition site. Anything else is
675 // a backwards compatibility hazard (and will break old versions of winapi for sure)
677 // note that validation may still cause a hard error on this very same constant,
678 // because any code that existed before validation could not have failed validation
679 // thus preventing such a hard error from being a backwards compatibility hazard
680 Some(DefKind::Const) | Some(DefKind::AssocConst) => {
681 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
683 tcx.at(tcx.def_span(def_id)),
684 "any use of this value will cause an error",
689 // promoting runtime code is only allowed to error if it references broken constants
690 // any other kind of error will be reported to the user as a deny-by-default lint
691 _ => if let Some(p) = cid.promoted {
692 let span = tcx.optimized_mir(def_id).promoted[p].span;
693 if let InterpError::ReferencedConstant = err.error {
696 "evaluation of constant expression failed",
701 "reaching this expression at runtime will panic or abort",
702 tcx.hir().as_local_hir_id(def_id).unwrap(),
706 // anything else (array lengths, enum initializers, constant patterns) are reported
711 "evaluation of constant value failed",
716 // use of broken constant from other crate
717 err.report_as_error(ecx.tcx, "could not evaluate constant")