1 // Copyright 2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 // Not in interpret to make sure we do not use private implementation details
14 use std::error::Error;
15 use std::borrow::{Borrow, Cow};
17 use std::collections::hash_map::Entry;
19 use rustc::hir::{self, def_id::DefId};
20 use rustc::hir::def::Def;
21 use rustc::mir::interpret::{ConstEvalErr, ErrorHandled};
23 use rustc::ty::{self, TyCtxt, Instance, query::TyCtxtAt};
24 use rustc::ty::layout::{self, LayoutOf, TyLayout, VariantIdx};
25 use rustc::ty::subst::Subst;
26 use rustc::traits::Reveal;
27 use rustc_data_structures::indexed_vec::IndexVec;
28 use rustc_data_structures::fx::FxHashMap;
29 use rustc::util::common::ErrorReported;
31 use syntax::ast::Mutability;
32 use syntax::source_map::{Span, DUMMY_SP};
34 use crate::interpret::{self,
35 PlaceTy, MPlaceTy, MemPlace, OpTy, Operand, Immediate, Scalar, RawConst, ConstValue, Pointer,
36 EvalResult, EvalError, EvalErrorKind, GlobalId, EvalContext, StackPopCleanup,
37 Allocation, AllocId, MemoryKind,
38 snapshot, RefTracking,
41 /// Number of steps until the detector even starts doing anything.
42 /// Also, a warning is shown to the user when this number is reached.
43 const STEPS_UNTIL_DETECTOR_ENABLED: isize = 1_000_000;
44 /// The number of steps between loop detector snapshots.
45 /// Should be a power of two for performance reasons.
46 const DETECTOR_SNAPSHOT_PERIOD: isize = 256;
48 pub fn mk_borrowck_eval_cx<'a, 'mir, 'tcx>(
49 tcx: TyCtxt<'a, 'tcx, 'tcx>,
50 instance: Instance<'tcx>,
51 mir: &'mir mir::Mir<'tcx>,
53 ) -> EvalResult<'tcx, CompileTimeEvalContext<'a, 'mir, 'tcx>> {
54 debug!("mk_borrowck_eval_cx: {:?}", instance);
55 let param_env = tcx.param_env(instance.def_id());
56 let mut ecx = EvalContext::new(tcx.at(span), param_env, CompileTimeInterpreter::new());
57 // insert a stack frame so any queries have the correct substs
58 // cannot use `push_stack_frame`; if we do `const_prop` explodes
59 ecx.stack.push(interpret::Frame {
60 block: mir::START_BLOCK,
61 locals: IndexVec::new(),
66 return_to_block: StackPopCleanup::Goto(None), // never pop
72 pub fn mk_eval_cx<'a, 'tcx>(
73 tcx: TyCtxt<'a, 'tcx, 'tcx>,
74 instance: Instance<'tcx>,
75 param_env: ty::ParamEnv<'tcx>,
76 ) -> EvalResult<'tcx, CompileTimeEvalContext<'a, 'tcx, 'tcx>> {
77 debug!("mk_eval_cx: {:?}, {:?}", instance, param_env);
78 let span = tcx.def_span(instance.def_id());
79 let mut ecx = EvalContext::new(tcx.at(span), param_env, CompileTimeInterpreter::new());
80 let mir = ecx.load_mir(instance.def)?;
81 // insert a stack frame so any queries have the correct substs
87 StackPopCleanup::Goto(None), // never pop
92 pub(crate) fn eval_promoted<'a, 'mir, 'tcx>(
93 tcx: TyCtxt<'a, 'tcx, 'tcx>,
95 mir: &'mir mir::Mir<'tcx>,
96 param_env: ty::ParamEnv<'tcx>,
97 ) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
98 let mut ecx = mk_borrowck_eval_cx(tcx, cid.instance, mir, DUMMY_SP).unwrap();
99 eval_body_using_ecx(&mut ecx, cid, Some(mir), param_env)
102 // FIXME: This thing is a bad hack. We should get rid of it. Ideally constants are always
104 pub fn op_to_const<'tcx>(
105 ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
108 ) -> EvalResult<'tcx, &'tcx ty::Const<'tcx>> {
109 // We do not normalize just any data. Only scalar layout and fat pointers.
110 let normalize = may_normalize
111 && match op.layout.abi {
112 layout::Abi::Scalar(..) => true,
113 layout::Abi::ScalarPair(..) => {
114 // Must be a fat pointer
115 op.layout.ty.builtin_deref(true).is_some()
119 let normalized_op = if normalize {
120 ecx.try_read_immediate(op)?
123 Operand::Indirect(mplace) => Err(mplace),
124 Operand::Immediate(val) => Ok(val)
127 let val = match normalized_op {
128 Err(MemPlace { ptr, align, meta }) => {
129 // extract alloc-offset pair
130 assert!(meta.is_none());
131 let ptr = ptr.to_ptr()?;
132 let alloc = ecx.memory.get(ptr.alloc_id)?;
133 assert!(alloc.align.abi() >= align.abi());
134 assert!(alloc.bytes.len() as u64 - ptr.offset.bytes() >= op.layout.size.bytes());
135 let mut alloc = alloc.clone();
137 // FIXME shouldn't it be the case that `mark_static_initialized` has already
138 // interned this? I thought that is the entire point of that `FinishStatic` stuff?
139 let alloc = ecx.tcx.intern_const_alloc(alloc);
140 ConstValue::ByRef(ptr.alloc_id, alloc, ptr.offset)
142 Ok(Immediate::Scalar(x)) =>
143 ConstValue::Scalar(x.not_undef()?),
144 Ok(Immediate::ScalarPair(a, b)) =>
145 ConstValue::ScalarPair(a.not_undef()?, b.not_undef()?),
147 Ok(ty::Const::from_const_value(ecx.tcx.tcx, val, op.layout.ty))
150 fn eval_body_and_ecx<'a, 'mir, 'tcx>(
151 tcx: TyCtxt<'a, 'tcx, 'tcx>,
153 mir: Option<&'mir mir::Mir<'tcx>>,
154 param_env: ty::ParamEnv<'tcx>,
155 ) -> (EvalResult<'tcx, MPlaceTy<'tcx>>, CompileTimeEvalContext<'a, 'mir, 'tcx>) {
156 // we start out with the best span we have
157 // and try improving it down the road when more information is available
158 let span = tcx.def_span(cid.instance.def_id());
159 let span = mir.map(|mir| mir.span).unwrap_or(span);
160 let mut ecx = EvalContext::new(tcx.at(span), param_env, CompileTimeInterpreter::new());
161 let r = eval_body_using_ecx(&mut ecx, cid, mir, param_env);
165 // Returns a pointer to where the result lives
166 fn eval_body_using_ecx<'mir, 'tcx>(
167 ecx: &mut CompileTimeEvalContext<'_, 'mir, 'tcx>,
169 mir: Option<&'mir mir::Mir<'tcx>>,
170 param_env: ty::ParamEnv<'tcx>,
171 ) -> EvalResult<'tcx, MPlaceTy<'tcx>> {
172 debug!("eval_body_using_ecx: {:?}, {:?}", cid, param_env);
173 let tcx = ecx.tcx.tcx;
174 let mut mir = match mir {
176 None => ecx.load_mir(cid.instance.def)?,
178 if let Some(index) = cid.promoted {
179 mir = &mir.promoted[index];
181 let layout = ecx.layout_of(mir.return_ty().subst(tcx, cid.instance.substs))?;
182 assert!(!layout.is_unsized());
183 let ret = ecx.allocate(layout, MemoryKind::Stack)?;
185 let name = ty::tls::with(|tcx| tcx.item_path_str(cid.instance.def_id()));
186 let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
187 trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
188 assert!(mir.arg_count == 0);
189 ecx.push_stack_frame(
194 StackPopCleanup::None { cleanup: false },
197 // The main interpreter loop.
201 let internally_mutable = !layout.ty.is_freeze(tcx, param_env, mir.span);
202 let is_static = tcx.is_static(cid.instance.def_id());
203 let mutability = if is_static == Some(hir::Mutability::MutMutable) || internally_mutable {
206 Mutability::Immutable
208 ecx.memory.intern_static(ret.ptr.to_ptr()?.alloc_id, mutability)?;
210 debug!("eval_body_using_ecx done: {:?}", *ret);
214 impl<'tcx> Into<EvalError<'tcx>> for ConstEvalError {
215 fn into(self) -> EvalError<'tcx> {
216 EvalErrorKind::MachineError(self.to_string()).into()
220 #[derive(Clone, Debug)]
221 enum ConstEvalError {
225 impl fmt::Display for ConstEvalError {
226 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
227 use self::ConstEvalError::*;
229 NeedsRfc(ref msg) => {
232 "\"{}\" needs an rfc before being allowed inside constants",
240 impl Error for ConstEvalError {
241 fn description(&self) -> &str {
242 use self::ConstEvalError::*;
244 NeedsRfc(_) => "this feature needs an rfc before being allowed inside constants",
248 fn cause(&self) -> Option<&dyn Error> {
253 // Extra machine state for CTFE, and the Machine instance
254 pub struct CompileTimeInterpreter<'a, 'mir, 'tcx: 'a+'mir> {
255 /// When this value is negative, it indicates the number of interpreter
256 /// steps *until* the loop detector is enabled. When it is positive, it is
257 /// the number of steps after the detector has been enabled modulo the loop
259 pub(super) steps_since_detector_enabled: isize,
261 /// Extra state to detect loops.
262 pub(super) loop_detector: snapshot::InfiniteLoopDetector<'a, 'mir, 'tcx>,
265 impl<'a, 'mir, 'tcx> CompileTimeInterpreter<'a, 'mir, 'tcx> {
267 CompileTimeInterpreter {
268 loop_detector: Default::default(),
269 steps_since_detector_enabled: -STEPS_UNTIL_DETECTOR_ENABLED,
274 impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
276 fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
279 FxHashMap::contains_key(self, k)
283 fn insert(&mut self, k: K, v: V) -> Option<V>
285 FxHashMap::insert(self, k, v)
289 fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
292 FxHashMap::remove(self, k)
296 fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
298 .filter_map(move |(k, v)| f(k, &*v))
306 vacant: impl FnOnce() -> Result<V, E>
313 bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
322 vacant: impl FnOnce() -> Result<V, E>
323 ) -> Result<&mut V, E>
325 match self.entry(k) {
326 Entry::Occupied(e) => Ok(e.into_mut()),
327 Entry::Vacant(e) => {
335 type CompileTimeEvalContext<'a, 'mir, 'tcx> =
336 EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>;
338 impl interpret::MayLeak for ! {
340 fn may_leak(self) -> bool {
341 // `self` is uninhabited
346 impl<'a, 'mir, 'tcx> interpret::Machine<'a, 'mir, 'tcx>
347 for CompileTimeInterpreter<'a, 'mir, 'tcx>
349 type MemoryKinds = !;
350 type AllocExtra = ();
351 type PointerTag = ();
353 type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
355 const STATIC_KIND: Option<!> = None; // no copying of statics allowed
358 fn enforce_validity(_ecx: &EvalContext<'a, 'mir, 'tcx, Self>) -> bool {
359 false // for now, we don't enforce validity
363 ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
364 instance: ty::Instance<'tcx>,
366 dest: Option<PlaceTy<'tcx>>,
367 ret: Option<mir::BasicBlock>,
368 ) -> EvalResult<'tcx, Option<&'mir mir::Mir<'tcx>>> {
369 debug!("eval_fn_call: {:?}", instance);
370 // Execution might have wandered off into other crates, so we cannot to a stability-
371 // sensitive check here. But we can at least rule out functions that are not const
373 if !ecx.tcx.is_const_fn_raw(instance.def_id()) {
374 // Some functions we support even if they are non-const -- but avoid testing
375 // that for const fn! We certainly do *not* want to actually call the fn
376 // though, so be sure we return here.
377 return if ecx.hook_fn(instance, args, dest)? {
378 ecx.goto_block(ret)?; // fully evaluated and done
381 err!(MachineError(format!("calling non-const function `{}`", instance)))
384 // This is a const fn. Call it.
385 Ok(Some(match ecx.load_mir(instance.def) {
388 if let EvalErrorKind::NoMirFor(ref path) = err.kind {
390 ConstEvalError::NeedsRfc(format!("calling extern function `{}`", path))
400 ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
401 instance: ty::Instance<'tcx>,
404 ) -> EvalResult<'tcx> {
405 if ecx.emulate_intrinsic(instance, args, dest)? {
408 // An intrinsic that we do not support
409 let intrinsic_name = &ecx.tcx.item_name(instance.def_id()).as_str()[..];
411 ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into()
416 _ecx: &EvalContext<'a, 'mir, 'tcx, Self>,
419 _left_layout: TyLayout<'tcx>,
421 _right_layout: TyLayout<'tcx>,
422 ) -> EvalResult<'tcx, (Scalar, bool)> {
424 ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into(),
428 fn find_foreign_static(
429 _tcx: TyCtxtAt<'a, 'tcx, 'tcx>,
431 ) -> EvalResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> {
432 err!(ReadForeignStatic)
436 fn adjust_static_allocation(
437 alloc: &'_ Allocation
438 ) -> Cow<'_, Allocation<Self::PointerTag>> {
439 // We do not use a tag so we can just cheaply forward the reference
444 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
445 _dest: PlaceTy<'tcx>,
446 ) -> EvalResult<'tcx> {
448 ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into(),
452 fn before_terminator(ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>) -> EvalResult<'tcx> {
454 let steps = &mut ecx.machine.steps_since_detector_enabled;
461 *steps %= DETECTOR_SNAPSHOT_PERIOD;
467 let span = ecx.frame().span;
468 ecx.machine.loop_detector.observe_and_analyze(
477 fn tag_new_allocation(
478 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
480 _kind: MemoryKind<Self::MemoryKinds>,
481 ) -> EvalResult<'tcx, Pointer> {
486 /// Project to a field of a (variant of a) const
487 pub fn const_field<'a, 'tcx>(
488 tcx: TyCtxt<'a, 'tcx, 'tcx>,
489 param_env: ty::ParamEnv<'tcx>,
490 instance: ty::Instance<'tcx>,
491 variant: Option<VariantIdx>,
493 value: &'tcx ty::Const<'tcx>,
494 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
495 trace!("const_field: {:?}, {:?}, {:?}", instance, field, value);
496 let ecx = mk_eval_cx(tcx, instance, param_env).unwrap();
498 // get the operand again
499 let op = ecx.const_to_op(value)?;
501 let down = match variant {
503 Some(variant) => ecx.operand_downcast(op, variant)?
506 let field = ecx.operand_field(down, field.index() as u64)?;
507 // and finally move back to the const world, always normalizing because
508 // this is not called for statics.
509 op_to_const(&ecx, field, true)
511 result.map_err(|error| {
512 let err = error_to_const_error(&ecx, error);
513 err.report_as_error(ecx.tcx, "could not access field of constant");
514 ErrorHandled::Reported
518 pub fn const_variant_index<'a, 'tcx>(
519 tcx: TyCtxt<'a, 'tcx, 'tcx>,
520 param_env: ty::ParamEnv<'tcx>,
521 instance: ty::Instance<'tcx>,
522 val: &'tcx ty::Const<'tcx>,
523 ) -> EvalResult<'tcx, VariantIdx> {
524 trace!("const_variant_index: {:?}, {:?}", instance, val);
525 let ecx = mk_eval_cx(tcx, instance, param_env).unwrap();
526 let op = ecx.const_to_op(val)?;
527 Ok(ecx.read_discriminant(op)?.1)
530 pub fn error_to_const_error<'a, 'mir, 'tcx>(
531 ecx: &EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>,
532 mut error: EvalError<'tcx>
533 ) -> ConstEvalErr<'tcx> {
534 error.print_backtrace();
535 let stacktrace = ecx.generate_stacktrace(None);
536 ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
539 fn validate_and_turn_into_const<'a, 'tcx>(
540 tcx: ty::TyCtxt<'a, 'tcx, '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, cid.instance, key.param_env).unwrap();
547 let op = ecx.raw_const_to_mplace(constant)?.into();
548 // FIXME: Once the visitor infrastructure landed, change validation to
549 // work directly on `MPlaceTy`.
550 let mut ref_tracking = RefTracking::new(op);
551 while let Some((op, path)) = ref_tracking.todo.pop() {
552 ecx.validate_operand(
555 Some(&mut ref_tracking),
556 /* const_mode */ true,
559 // Now that we validated, turn this into a proper constant
560 let def_id = cid.instance.def.def_id();
561 let normalize = tcx.is_static(def_id).is_none() && cid.promoted.is_none();
562 op_to_const(&ecx, op, normalize)
565 val.map_err(|error| {
566 let err = error_to_const_error(&ecx, error);
567 match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
569 diag.note("The rules on what exactly is undefined behavior aren't clear, \
570 so this check might be overzealous. Please open an issue on the rust compiler \
571 repository if you believe it should not be considered undefined behavior",
574 ErrorHandled::Reported
581 pub fn const_eval_provider<'a, 'tcx>(
582 tcx: TyCtxt<'a, 'tcx, 'tcx>,
583 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
584 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
585 // see comment in const_eval_provider for what we're doing here
586 if key.param_env.reveal == Reveal::All {
587 let mut key = key.clone();
588 key.param_env.reveal = Reveal::UserFacing;
589 match tcx.const_eval(key) {
590 // try again with reveal all as requested
591 Err(ErrorHandled::TooGeneric) => {
592 // Promoteds should never be "too generic" when getting evaluated.
593 // They either don't get evaluated, or we are in a monomorphic context
594 assert!(key.value.promoted.is_none());
597 other => return other,
600 tcx.const_eval_raw(key).and_then(|val| {
601 validate_and_turn_into_const(tcx, val, key)
605 pub fn const_eval_raw_provider<'a, 'tcx>(
606 tcx: TyCtxt<'a, 'tcx, 'tcx>,
607 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
608 ) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
609 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
610 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
611 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
612 // computed. For a large percentage of constants that will already have succeeded. Only
613 // associated constants of generic functions will fail due to not enough monomorphization
614 // information being available.
616 // In case we fail in the `UserFacing` variant, we just do the real computation.
617 if key.param_env.reveal == Reveal::All {
618 let mut key = key.clone();
619 key.param_env.reveal = Reveal::UserFacing;
620 match tcx.const_eval_raw(key) {
621 // try again with reveal all as requested
622 Err(ErrorHandled::TooGeneric) => {},
624 other => return other,
627 // the first trace is for replicating an ice
628 // There's no tracking issue, but the next two lines concatenated link to the discussion on
629 // zulip. It's not really possible to test this, because it doesn't show up in diagnostics
631 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
632 // subject/anon_const_instance_printing/near/135980032
633 trace!("const eval: {}", key.value.instance);
634 trace!("const eval: {:?}", key);
637 let def_id = cid.instance.def.def_id();
639 if let Some(id) = tcx.hir.as_local_node_id(def_id) {
640 let tables = tcx.typeck_tables_of(def_id);
642 // Do match-check before building MIR
643 if let Err(ErrorReported) = tcx.check_match(def_id) {
644 return Err(ErrorHandled::Reported)
647 if let hir::BodyOwnerKind::Const = tcx.hir.body_owner_kind(id) {
648 tcx.mir_const_qualif(def_id);
651 // Do not continue into miri if typeck errors occurred; it will fail horribly
652 if tables.tainted_by_errors {
653 return Err(ErrorHandled::Reported)
657 let (res, ecx) = eval_body_and_ecx(tcx, cid, None, key.param_env);
658 res.and_then(|place| {
660 alloc_id: place.to_ptr().expect("we allocated this ptr!").alloc_id,
664 let err = error_to_const_error(&ecx, error);
665 // errors in statics are always emitted as fatal errors
666 if tcx.is_static(def_id).is_some() {
667 let err = err.report_as_error(ecx.tcx, "could not evaluate static initializer");
668 // check that a static never produces `TooGeneric`
669 if tcx.sess.err_count() == 0 {
670 span_bug!(ecx.tcx.span, "static eval failure didn't emit an error: {:#?}", err);
673 } else if def_id.is_local() {
674 // constant defined in this crate, we can figure out a lint level!
675 match tcx.describe_def(def_id) {
676 // constants never produce a hard error at the definition site. Anything else is
677 // a backwards compatibility hazard (and will break old versions of winapi for sure)
679 // note that validation may still cause a hard error on this very same constant,
680 // because any code that existed before validation could not have failed validation
681 // thus preventing such a hard error from being a backwards compatibility hazard
682 Some(Def::Const(_)) | Some(Def::AssociatedConst(_)) => {
683 let node_id = tcx.hir.as_local_node_id(def_id).unwrap();
685 tcx.at(tcx.def_span(def_id)),
686 "any use of this value will cause an error",
690 // promoting runtime code is only allowed to error if it references broken constants
691 // any other kind of error will be reported to the user as a deny-by-default lint
692 _ => if let Some(p) = cid.promoted {
693 let span = tcx.optimized_mir(def_id).promoted[p].span;
694 if let EvalErrorKind::ReferencedConstant = err.error {
697 "evaluation of constant expression failed",
702 "reaching this expression at runtime will panic or abort",
703 tcx.hir.as_local_node_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")