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, Ty, TyCtxt, subst::Subst};
15 use rustc::ty::layout::{self, LayoutOf, VariantIdx};
16 use rustc::traits::Reveal;
17 use rustc_data_structures::fx::FxHashMap;
18 use crate::interpret::eval_nullary_intrinsic;
20 use syntax::source_map::{Span, DUMMY_SP};
22 use crate::interpret::{self,
23 PlaceTy, MPlaceTy, OpTy, ImmTy, Immediate, Scalar, Pointer,
25 InterpResult, InterpErrorInfo, GlobalId, InterpCx, StackPopCleanup,
26 Allocation, AllocId, MemoryKind, Memory,
27 snapshot, RefTracking, intern_const_alloc_recursive,
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 `InterpCx` 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<'mir, 'tcx>(
47 param_env: ty::ParamEnv<'tcx>,
48 ) -> CompileTimeEvalContext<'mir, 'tcx> {
49 debug!("mk_eval_cx: {:?}", param_env);
50 InterpCx::new(tcx.at(span), param_env, CompileTimeInterpreter::new(), Default::default())
54 ecx: &CompileTimeEvalContext<'_, 'tcx>,
56 ) -> &'tcx ty::Const<'tcx> {
57 // We do not have value optmizations for everything.
58 // Only scalars and slices, since they are very common.
59 // Note that further down we turn scalars of undefined bits back to `ByRef`. These can result
60 // from scalar unions that are initialized with one of their zero sized variants. We could
61 // instead allow `ConstValue::Scalar` to store `ScalarMaybeUndef`, but that would affect all
62 // the usual cases of extracting e.g. a `usize`, without there being a real use case for the
64 let try_as_immediate = match op.layout.abi {
65 layout::Abi::Scalar(..) => true,
66 layout::Abi::ScalarPair(..) => match op.layout.ty.sty {
67 ty::Ref(_, inner, _) => match inner.sty {
68 ty::Slice(elem) => elem == ecx.tcx.types.u8,
76 let immediate = if try_as_immediate {
77 Err(ecx.read_immediate(op).expect("normalization works on validated constants"))
79 // It is guaranteed that any non-slice scalar pair is actually ByRef here.
80 // When we come back from raw const eval, we are always by-ref. The only way our op here is
81 // by-val is if we are in const_field, i.e., if this is (a field of) something that we
82 // "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
83 // structs containing such.
86 let val = match immediate {
88 let ptr = mplace.ptr.to_ptr().unwrap();
89 let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
90 ConstValue::ByRef { alloc, offset: ptr.offset }
92 // see comment on `let try_as_immediate` above
93 Err(ImmTy { imm: Immediate::Scalar(x), .. }) => match x {
94 ScalarMaybeUndef::Scalar(s) => ConstValue::Scalar(s),
95 ScalarMaybeUndef::Undef => {
96 // When coming out of "normal CTFE", we'll always have an `Indirect` operand as
97 // argument and we will not need this. The only way we can already have an
98 // `Immediate` is when we are called from `const_field`, and that `Immediate`
99 // comes from a constant so it can happen have `Undef`, because the indirect
100 // memory that was read had undefined bytes.
101 let mplace = op.assert_mem_place();
102 let ptr = mplace.ptr.to_ptr().unwrap();
103 let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
104 ConstValue::ByRef { alloc, offset: ptr.offset }
107 Err(ImmTy { imm: Immediate::ScalarPair(a, b), .. }) => {
108 let (data, start) = match a.not_undef().unwrap() {
109 Scalar::Ptr(ptr) => (
110 ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id),
113 Scalar::Raw { .. } => (
114 ecx.tcx.intern_const_alloc(Allocation::from_byte_aligned_bytes(
120 let len = b.to_usize(&ecx.tcx.tcx).unwrap();
121 let start = start.try_into().unwrap();
122 let len: usize = len.try_into().unwrap();
130 ecx.tcx.mk_const(ty::Const { val, ty: op.layout.ty })
133 // Returns a pointer to where the result lives
134 fn eval_body_using_ecx<'mir, 'tcx>(
135 ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
137 body: &'mir mir::Body<'tcx>,
138 ) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
139 debug!("eval_body_using_ecx: {:?}, {:?}", cid, ecx.param_env);
140 let tcx = ecx.tcx.tcx;
141 let layout = ecx.layout_of(body.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.def_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!(body.arg_count == 0);
149 ecx.push_stack_frame(
154 StackPopCleanup::None { cleanup: false },
157 // The main interpreter loop.
161 intern_const_alloc_recursive(
163 cid.instance.def_id(),
167 debug!("eval_body_using_ecx done: {:?}", *ret);
171 #[derive(Clone, Debug)]
172 enum ConstEvalError {
176 impl<'tcx> Into<InterpErrorInfo<'tcx>> for ConstEvalError {
177 fn into(self) -> InterpErrorInfo<'tcx> {
178 err_unsup!(Unsupported(self.to_string())).into()
182 impl fmt::Display for ConstEvalError {
183 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
184 use self::ConstEvalError::*;
186 NeedsRfc(ref msg) => {
189 "\"{}\" needs an rfc before being allowed inside constants",
197 impl Error for ConstEvalError {
198 fn description(&self) -> &str {
199 use self::ConstEvalError::*;
201 NeedsRfc(_) => "this feature needs an rfc before being allowed inside constants",
205 fn cause(&self) -> Option<&dyn Error> {
210 // Extra machine state for CTFE, and the Machine instance
211 pub struct CompileTimeInterpreter<'mir, 'tcx> {
212 /// When this value is negative, it indicates the number of interpreter
213 /// steps *until* the loop detector is enabled. When it is positive, it is
214 /// the number of steps after the detector has been enabled modulo the loop
216 pub(super) steps_since_detector_enabled: isize,
218 /// Extra state to detect loops.
219 pub(super) loop_detector: snapshot::InfiniteLoopDetector<'mir, 'tcx>,
222 impl<'mir, 'tcx> CompileTimeInterpreter<'mir, 'tcx> {
224 CompileTimeInterpreter {
225 loop_detector: Default::default(),
226 steps_since_detector_enabled: -STEPS_UNTIL_DETECTOR_ENABLED,
231 impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
233 fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
236 FxHashMap::contains_key(self, k)
240 fn insert(&mut self, k: K, v: V) -> Option<V>
242 FxHashMap::insert(self, k, v)
246 fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
249 FxHashMap::remove(self, k)
253 fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
255 .filter_map(move |(k, v)| f(k, &*v))
263 vacant: impl FnOnce() -> Result<V, E>
270 bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
279 vacant: impl FnOnce() -> Result<V, E>
280 ) -> Result<&mut V, E>
282 match self.entry(k) {
283 Entry::Occupied(e) => Ok(e.into_mut()),
284 Entry::Vacant(e) => {
292 crate type CompileTimeEvalContext<'mir, 'tcx> =
293 InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>;
295 impl interpret::MayLeak for ! {
297 fn may_leak(self) -> bool {
298 // `self` is uninhabited
303 impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir, 'tcx> {
304 type MemoryKinds = !;
305 type PointerTag = ();
308 type FrameExtra = ();
309 type MemoryExtra = ();
310 type AllocExtra = ();
312 type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
314 const STATIC_KIND: Option<!> = None; // no copying of statics allowed
316 // We do not check for alignment to avoid having to carry an `Align`
317 // in `ConstValue::ByRef`.
318 const CHECK_ALIGN: bool = false;
321 fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
322 false // for now, we don't enforce validity
326 ecx: &mut InterpCx<'mir, 'tcx, Self>,
327 instance: ty::Instance<'tcx>,
329 dest: Option<PlaceTy<'tcx>>,
330 ret: Option<mir::BasicBlock>,
331 ) -> InterpResult<'tcx, Option<&'mir mir::Body<'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 do 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 throw_unsup_format!("calling non-const function `{}`", instance)
350 // This is a const fn. Call it.
351 Ok(Some(match ecx.load_mir(instance.def, None) {
354 if let err_unsup!(NoMirFor(ref path)) = err.kind {
356 ConstEvalError::NeedsRfc(format!("calling extern function `{}`", path))
366 _ecx: &mut InterpCx<'mir, 'tcx, Self>,
368 _args: &[OpTy<'tcx>],
369 _dest: Option<PlaceTy<'tcx>>,
370 _ret: Option<mir::BasicBlock>,
371 ) -> InterpResult<'tcx> {
376 ecx: &mut InterpCx<'mir, 'tcx, Self>,
377 instance: ty::Instance<'tcx>,
380 ) -> InterpResult<'tcx> {
381 if ecx.emulate_intrinsic(instance, args, dest)? {
384 // An intrinsic that we do not support
385 let intrinsic_name = ecx.tcx.item_name(instance.def_id());
387 ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into()
392 _mem: &Memory<'mir, 'tcx, Self>,
394 ) -> InterpResult<'tcx, u64> {
396 ConstEvalError::NeedsRfc("pointer-to-integer cast".to_string()).into(),
401 _ecx: &InterpCx<'mir, 'tcx, Self>,
405 ) -> InterpResult<'tcx, (Scalar, bool, Ty<'tcx>)> {
407 ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into(),
411 fn find_foreign_static(
414 ) -> InterpResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> {
415 throw_unsup!(ReadForeignStatic)
419 fn tag_allocation<'b>(
422 alloc: Cow<'b, Allocation>,
423 _kind: Option<MemoryKind<!>>,
424 ) -> (Cow<'b, Allocation<Self::PointerTag>>, Self::PointerTag) {
425 // We do not use a tag so we can just cheaply forward the allocation
430 fn tag_static_base_pointer(
433 ) -> Self::PointerTag {
438 _ecx: &mut InterpCx<'mir, 'tcx, Self>,
439 _dest: PlaceTy<'tcx>,
440 ) -> InterpResult<'tcx> {
442 ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into(),
446 fn before_terminator(ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
448 let steps = &mut ecx.machine.steps_since_detector_enabled;
455 *steps %= DETECTOR_SNAPSHOT_PERIOD;
461 let span = ecx.frame().span;
462 ecx.machine.loop_detector.observe_and_analyze(
471 fn stack_push(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
475 /// Called immediately before a stack frame gets popped.
477 fn stack_pop(_ecx: &mut InterpCx<'mir, 'tcx, Self>, _extra: ()) -> InterpResult<'tcx> {
482 /// Extracts a field of a (variant of a) const.
483 // this function uses `unwrap` copiously, because an already validated constant must have valid
484 // fields and can thus never fail outside of compiler bugs
485 pub fn const_field<'tcx>(
487 param_env: ty::ParamEnv<'tcx>,
488 variant: Option<VariantIdx>,
490 value: &'tcx ty::Const<'tcx>,
491 ) -> &'tcx ty::Const<'tcx> {
492 trace!("const_field: {:?}, {:?}", field, value);
493 let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
494 // get the operand again
495 let op = ecx.eval_const_to_op(value, None).unwrap();
497 let down = match variant {
499 Some(variant) => ecx.operand_downcast(op, variant).unwrap(),
502 let field = ecx.operand_field(down, field.index() as u64).unwrap();
503 // and finally move back to the const world, always normalizing because
504 // this is not called for statics.
505 op_to_const(&ecx, field)
508 // this function uses `unwrap` copiously, because an already validated constant must have valid
509 // fields and can thus never fail outside of compiler bugs
510 pub fn const_variant_index<'tcx>(
512 param_env: ty::ParamEnv<'tcx>,
513 val: &'tcx ty::Const<'tcx>,
515 trace!("const_variant_index: {:?}", val);
516 let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
517 let op = ecx.eval_const_to_op(val, None).unwrap();
518 ecx.read_discriminant(op).unwrap().1
521 /// Turn an interpreter error into something to report to the user.
522 /// As a side-effect, if RUSTC_CTFE_BACKTRACE is set, this prints the backtrace.
523 /// Should be called only if the error is actually going to to be reported!
524 pub fn error_to_const_error<'mir, 'tcx>(
525 ecx: &InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>,
526 mut error: InterpErrorInfo<'tcx>,
527 ) -> ConstEvalErr<'tcx> {
528 error.print_backtrace();
529 let stacktrace = ecx.generate_stacktrace(None);
530 ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
533 pub fn note_on_undefined_behavior_error() -> &'static str {
534 "The rules on what exactly is undefined behavior aren't clear, \
535 so this check might be overzealous. Please open an issue on the rustc \
536 repository if you believe it should not be considered undefined behavior."
539 fn validate_and_turn_into_const<'tcx>(
541 constant: RawConst<'tcx>,
542 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
543 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
545 let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env);
547 let mplace = ecx.raw_const_to_mplace(constant)?;
548 let mut ref_tracking = RefTracking::new(mplace);
549 while let Some((mplace, path)) = ref_tracking.todo.pop() {
550 ecx.validate_operand(
553 Some(&mut ref_tracking),
556 // Now that we validated, turn this into a proper constant.
557 // Statics/promoteds are always `ByRef`, for the rest `op_to_const` decides
558 // whether they become immediates.
559 let def_id = cid.instance.def.def_id();
560 if tcx.is_static(def_id) || cid.promoted.is_some() {
561 let ptr = mplace.ptr.to_ptr()?;
562 Ok(tcx.mk_const(ty::Const {
563 val: ConstValue::ByRef {
564 alloc: ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id),
567 ty: mplace.layout.ty,
570 Ok(op_to_const(&ecx, mplace.into()))
574 val.map_err(|error| {
575 let err = error_to_const_error(&ecx, error);
576 match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
578 diag.note(note_on_undefined_behavior_error());
580 ErrorHandled::Reported
587 pub fn const_eval_provider<'tcx>(
589 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
590 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
591 // see comment in const_eval_raw_provider for what we're doing here
592 if key.param_env.reveal == Reveal::All {
593 let mut key = key.clone();
594 key.param_env.reveal = Reveal::UserFacing;
595 match tcx.const_eval(key) {
596 // try again with reveal all as requested
597 Err(ErrorHandled::TooGeneric) => {
598 // Promoteds should never be "too generic" when getting evaluated.
599 // They either don't get evaluated, or we are in a monomorphic context
600 assert!(key.value.promoted.is_none());
603 other => return other,
607 // We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
608 // Catch such calls and evaluate them instead of trying to load a constant's MIR.
609 if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
610 let ty = key.value.instance.ty(tcx);
611 let substs = match ty.sty {
612 ty::FnDef(_, substs) => substs,
613 _ => bug!("intrinsic with type {:?}", ty),
615 return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs)
617 let span = tcx.def_span(def_id);
618 let error = ConstEvalErr { error: error.kind, stacktrace: vec![], span };
619 error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
623 tcx.const_eval_raw(key).and_then(|val| {
624 validate_and_turn_into_const(tcx, val, key)
628 pub fn const_eval_raw_provider<'tcx>(
630 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
631 ) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
632 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
633 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
634 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
635 // computed. For a large percentage of constants that will already have succeeded. Only
636 // associated constants of generic functions will fail due to not enough monomorphization
637 // information being available.
639 // In case we fail in the `UserFacing` variant, we just do the real computation.
640 if key.param_env.reveal == Reveal::All {
641 let mut key = key.clone();
642 key.param_env.reveal = Reveal::UserFacing;
643 match tcx.const_eval_raw(key) {
644 // try again with reveal all as requested
645 Err(ErrorHandled::TooGeneric) => {},
647 other => return other,
650 if cfg!(debug_assertions) {
651 // Make sure we format the instance even if we do not print it.
652 // This serves as a regression test against an ICE on printing.
653 // The next two lines concatenated contain some discussion:
654 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
655 // subject/anon_const_instance_printing/near/135980032
656 let instance = key.value.instance.to_string();
657 trace!("const eval: {:?} ({})", key, instance);
661 let def_id = cid.instance.def.def_id();
663 if def_id.is_local() && tcx.typeck_tables_of(def_id).tainted_by_errors {
664 return Err(ErrorHandled::Reported);
667 let span = tcx.def_span(cid.instance.def_id());
668 let mut ecx = InterpCx::new(
671 CompileTimeInterpreter::new(),
675 let res = ecx.load_mir(cid.instance.def, cid.promoted);
677 |body| eval_body_using_ecx(&mut ecx, cid, body)
680 alloc_id: place.ptr.assert_ptr().alloc_id,
684 let err = error_to_const_error(&ecx, error);
685 // errors in statics are always emitted as fatal errors
686 if tcx.is_static(def_id) {
687 // Ensure that if the above error was either `TooGeneric` or `Reported`
688 // an error must be reported.
689 let v = err.report_as_error(ecx.tcx, "could not evaluate static initializer");
690 tcx.sess.delay_span_bug(
692 &format!("static eval failure did not emit an error: {:#?}", v)
695 } else if def_id.is_local() {
696 // constant defined in this crate, we can figure out a lint level!
697 match tcx.def_kind(def_id) {
698 // constants never produce a hard error at the definition site. Anything else is
699 // a backwards compatibility hazard (and will break old versions of winapi for sure)
701 // note that validation may still cause a hard error on this very same constant,
702 // because any code that existed before validation could not have failed validation
703 // thus preventing such a hard error from being a backwards compatibility hazard
704 Some(DefKind::Const) | Some(DefKind::AssocConst) => {
705 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
707 tcx.at(tcx.def_span(def_id)),
708 "any use of this value will cause an error",
713 // promoting runtime code is only allowed to error if it references broken constants
714 // any other kind of error will be reported to the user as a deny-by-default lint
715 _ => if let Some(p) = cid.promoted {
716 let span = tcx.promoted_mir(def_id)[p].span;
717 if let err_inval!(ReferencedConstant) = err.error {
720 "evaluation of constant expression failed",
725 "reaching this expression at runtime will panic or abort",
726 tcx.hir().as_local_hir_id(def_id).unwrap(),
730 // anything else (array lengths, enum initializers, constant patterns) are reported
735 "evaluation of constant value failed",
740 // use of broken constant from other crate
741 err.report_as_error(ecx.tcx, "could not evaluate constant")