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};
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};
35 PlaceTy, MemPlace, OpTy, Operand, Value, Scalar, 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, OpTy<'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 pub fn op_to_const<'tcx>(
103 ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
106 ) -> EvalResult<'tcx, &'tcx ty::Const<'tcx>> {
107 // We do not normalize just any data. Only scalar layout and fat pointers.
108 let normalize = may_normalize
109 && match op.layout.abi {
110 layout::Abi::Scalar(..) => true,
111 layout::Abi::ScalarPair(..) => {
112 // Must be a fat pointer
113 op.layout.ty.builtin_deref(true).is_some()
117 let normalized_op = if normalize {
118 ecx.try_read_value(op)?
121 Operand::Indirect(mplace) => Err(mplace),
122 Operand::Immediate(val) => Ok(val)
125 let val = match normalized_op {
126 Err(MemPlace { ptr, align, meta }) => {
127 // extract alloc-offset pair
128 assert!(meta.is_none());
129 let ptr = ptr.to_ptr()?;
130 let alloc = ecx.memory.get(ptr.alloc_id)?;
131 assert!(alloc.align.abi() >= align.abi());
132 assert!(alloc.bytes.len() as u64 - ptr.offset.bytes() >= op.layout.size.bytes());
133 let mut alloc = alloc.clone();
135 // FIXME shouldn't it be the case that `mark_static_initialized` has already
136 // interned this? I thought that is the entire point of that `FinishStatic` stuff?
137 let alloc = ecx.tcx.intern_const_alloc(alloc);
138 ConstValue::ByRef(ptr.alloc_id, alloc, ptr.offset)
140 Ok(Value::Scalar(x)) =>
141 ConstValue::Scalar(x.not_undef()?),
142 Ok(Value::ScalarPair(a, b)) =>
143 ConstValue::ScalarPair(a.not_undef()?, b.not_undef()?),
145 Ok(ty::Const::from_const_value(ecx.tcx.tcx, val, op.layout.ty))
148 fn eval_body_and_ecx<'a, 'mir, 'tcx>(
149 tcx: TyCtxt<'a, 'tcx, 'tcx>,
151 mir: Option<&'mir mir::Mir<'tcx>>,
152 param_env: ty::ParamEnv<'tcx>,
153 ) -> (EvalResult<'tcx, OpTy<'tcx>>, CompileTimeEvalContext<'a, 'mir, 'tcx>) {
154 // we start out with the best span we have
155 // and try improving it down the road when more information is available
156 let span = tcx.def_span(cid.instance.def_id());
157 let span = mir.map(|mir| mir.span).unwrap_or(span);
158 let mut ecx = EvalContext::new(tcx.at(span), param_env, CompileTimeInterpreter::new());
159 let r = eval_body_using_ecx(&mut ecx, cid, mir, param_env);
163 // Returns a pointer to where the result lives
164 fn eval_body_using_ecx<'mir, 'tcx>(
165 ecx: &mut CompileTimeEvalContext<'_, 'mir, 'tcx>,
167 mir: Option<&'mir mir::Mir<'tcx>>,
168 param_env: ty::ParamEnv<'tcx>,
169 ) -> EvalResult<'tcx, OpTy<'tcx>> {
170 debug!("eval_body_using_ecx: {:?}, {:?}", cid, param_env);
171 let tcx = ecx.tcx.tcx;
172 let mut mir = match mir {
174 None => ecx.load_mir(cid.instance.def)?,
176 if let Some(index) = cid.promoted {
177 mir = &mir.promoted[index];
179 let layout = ecx.layout_of(mir.return_ty().subst(tcx, cid.instance.substs))?;
180 assert!(!layout.is_unsized());
181 let ret = ecx.allocate(layout, MemoryKind::Stack)?;
183 let name = ty::tls::with(|tcx| tcx.item_path_str(cid.instance.def_id()));
184 let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
185 trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
186 assert!(mir.arg_count == 0);
187 ecx.push_stack_frame(
192 StackPopCleanup::None { cleanup: false },
195 // The main interpreter loop.
199 let internally_mutable = !layout.ty.is_freeze(tcx, param_env, mir.span);
200 let is_static = tcx.is_static(cid.instance.def_id());
201 let mutability = if is_static == Some(hir::Mutability::MutMutable) || internally_mutable {
204 Mutability::Immutable
206 ecx.memory.intern_static(ret.ptr.to_ptr()?.alloc_id, mutability)?;
208 debug!("eval_body_using_ecx done: {:?}", *ret);
212 impl<'tcx> Into<EvalError<'tcx>> for ConstEvalError {
213 fn into(self) -> EvalError<'tcx> {
214 EvalErrorKind::MachineError(self.to_string()).into()
218 #[derive(Clone, Debug)]
219 enum ConstEvalError {
223 impl fmt::Display for ConstEvalError {
224 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
225 use self::ConstEvalError::*;
227 NeedsRfc(ref msg) => {
230 "\"{}\" needs an rfc before being allowed inside constants",
238 impl Error for ConstEvalError {
239 fn description(&self) -> &str {
240 use self::ConstEvalError::*;
242 NeedsRfc(_) => "this feature needs an rfc before being allowed inside constants",
246 fn cause(&self) -> Option<&dyn Error> {
251 // Extra machine state for CTFE, and the Machine instance
252 pub struct CompileTimeInterpreter<'a, 'mir, 'tcx: 'a+'mir> {
253 /// When this value is negative, it indicates the number of interpreter
254 /// steps *until* the loop detector is enabled. When it is positive, it is
255 /// the number of steps after the detector has been enabled modulo the loop
257 pub(super) steps_since_detector_enabled: isize,
259 /// Extra state to detect loops.
260 pub(super) loop_detector: snapshot::InfiniteLoopDetector<'a, 'mir, 'tcx>,
263 impl<'a, 'mir, 'tcx> CompileTimeInterpreter<'a, 'mir, 'tcx> {
265 CompileTimeInterpreter {
266 loop_detector: Default::default(),
267 steps_since_detector_enabled: -STEPS_UNTIL_DETECTOR_ENABLED,
272 impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
274 fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
277 FxHashMap::contains_key(self, k)
281 fn insert(&mut self, k: K, v: V) -> Option<V>
283 FxHashMap::insert(self, k, v)
287 fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
290 FxHashMap::remove(self, k)
294 fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
296 .filter_map(move |(k, v)| f(k, &*v))
304 vacant: impl FnOnce() -> Result<V, E>
311 bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
320 vacant: impl FnOnce() -> Result<V, E>
321 ) -> Result<&mut V, E>
323 match self.entry(k) {
324 Entry::Occupied(e) => Ok(e.into_mut()),
325 Entry::Vacant(e) => {
333 type CompileTimeEvalContext<'a, 'mir, 'tcx> =
334 EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>;
336 impl interpret::MayLeak for ! {
338 fn may_leak(self) -> bool {
339 // `self` is uninhabited
344 impl<'a, 'mir, 'tcx> interpret::Machine<'a, 'mir, 'tcx>
345 for CompileTimeInterpreter<'a, 'mir, 'tcx>
347 type MemoryKinds = !;
348 type AllocExtra = ();
349 type PointerTag = ();
351 type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
353 const STATIC_KIND: Option<!> = None; // no copying of statics allowed
354 const ENABLE_PTR_TRACKING_HOOKS: bool = false; // we don't have no provenance
357 fn enforce_validity(_ecx: &EvalContext<'a, 'mir, 'tcx, Self>) -> bool {
358 false // for now, we don't enforce validity
362 ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
363 instance: ty::Instance<'tcx>,
365 dest: Option<PlaceTy<'tcx>>,
366 ret: Option<mir::BasicBlock>,
367 ) -> EvalResult<'tcx, Option<&'mir mir::Mir<'tcx>>> {
368 debug!("eval_fn_call: {:?}", instance);
369 if !ecx.tcx.is_const_fn(instance.def_id()) {
370 // Some functions we support even if they are non-const -- but avoid testing
371 // that for const fn!
372 if ecx.hook_fn(instance, args, dest)? {
373 ecx.goto_block(ret)?; // fully evaluated and done
377 // This is a const fn. Call it.
378 Ok(Some(match ecx.load_mir(instance.def) {
381 if let EvalErrorKind::NoMirFor(ref path) = err.kind {
383 ConstEvalError::NeedsRfc(format!("calling extern function `{}`", path))
393 ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
394 instance: ty::Instance<'tcx>,
397 ) -> EvalResult<'tcx> {
398 if ecx.emulate_intrinsic(instance, args, dest)? {
401 // An intrinsic that we do not support
402 let intrinsic_name = &ecx.tcx.item_name(instance.def_id()).as_str()[..];
404 ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into()
409 _ecx: &EvalContext<'a, 'mir, 'tcx, Self>,
412 _left_layout: TyLayout<'tcx>,
414 _right_layout: TyLayout<'tcx>,
415 ) -> EvalResult<'tcx, (Scalar, bool)> {
417 ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into(),
421 fn find_foreign_static(
422 _tcx: TyCtxtAt<'a, 'tcx, 'tcx>,
424 ) -> EvalResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> {
425 err!(ReadForeignStatic)
429 fn adjust_static_allocation(
430 alloc: &'_ Allocation
431 ) -> Cow<'_, Allocation<Self::PointerTag>> {
432 // We do not use a tag so we can just cheaply forward the reference
437 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
438 _dest: PlaceTy<'tcx>,
439 ) -> EvalResult<'tcx> {
441 ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into(),
445 fn before_terminator(ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>) -> EvalResult<'tcx> {
447 let steps = &mut ecx.machine.steps_since_detector_enabled;
454 *steps %= DETECTOR_SNAPSHOT_PERIOD;
460 let span = ecx.frame().span;
461 ecx.machine.loop_detector.observe_and_analyze(
470 fn tag_new_allocation(
471 _ecx: &mut EvalContext<'a, 'mir, 'tcx, Self>,
473 _kind: MemoryKind<Self::MemoryKinds>,
474 ) -> EvalResult<'tcx, Pointer> {
479 /// Project to a field of a (variant of a) const
480 pub fn const_field<'a, 'tcx>(
481 tcx: TyCtxt<'a, 'tcx, 'tcx>,
482 param_env: ty::ParamEnv<'tcx>,
483 instance: ty::Instance<'tcx>,
484 variant: Option<usize>,
486 value: &'tcx ty::Const<'tcx>,
487 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
488 trace!("const_field: {:?}, {:?}, {:?}", instance, field, value);
489 let ecx = mk_eval_cx(tcx, instance, param_env).unwrap();
491 // get the operand again
492 let op = ecx.const_to_op(value)?;
494 let down = match variant {
496 Some(variant) => ecx.operand_downcast(op, variant)?
499 let field = ecx.operand_field(down, field.index() as u64)?;
500 // and finally move back to the const world, always normalizing because
501 // this is not called for statics.
502 op_to_const(&ecx, field, true)
504 result.map_err(|error| {
505 let err = error_to_const_error(&ecx, error);
506 err.report_as_error(ecx.tcx, "could not access field of constant");
507 ErrorHandled::Reported
511 pub fn const_variant_index<'a, 'tcx>(
512 tcx: TyCtxt<'a, 'tcx, 'tcx>,
513 param_env: ty::ParamEnv<'tcx>,
514 instance: ty::Instance<'tcx>,
515 val: &'tcx ty::Const<'tcx>,
516 ) -> EvalResult<'tcx, usize> {
517 trace!("const_variant_index: {:?}, {:?}", instance, val);
518 let ecx = mk_eval_cx(tcx, instance, param_env).unwrap();
519 let op = ecx.const_to_op(val)?;
520 Ok(ecx.read_discriminant(op)?.1)
523 pub fn error_to_const_error<'a, 'mir, 'tcx>(
524 ecx: &EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>,
525 mut error: EvalError<'tcx>
526 ) -> ConstEvalErr<'tcx> {
527 error.print_backtrace();
528 let stacktrace = ecx.generate_stacktrace(None);
529 ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
532 fn validate_const<'a, 'tcx>(
533 tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
534 constant: &'tcx ty::Const<'tcx>,
535 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
536 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
538 let ecx = mk_eval_cx(tcx, cid.instance, key.param_env).unwrap();
540 let op = ecx.const_to_op(constant)?;
541 let mut ref_tracking = RefTracking::new(op);
542 while let Some((op, mut path)) = ref_tracking.todo.pop() {
543 ecx.validate_operand(
546 Some(&mut ref_tracking),
547 /* const_mode */ true,
553 val.map_err(|error| {
554 let err = error_to_const_error(&ecx, error);
555 match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
557 diag.note("The rules on what exactly is undefined behavior aren't clear, \
558 so this check might be overzealous. Please open an issue on the rust compiler \
559 repository if you believe it should not be considered undefined behavior",
562 ErrorHandled::Reported
569 pub fn const_eval_provider<'a, 'tcx>(
570 tcx: TyCtxt<'a, 'tcx, 'tcx>,
571 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
572 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
573 // see comment in const_eval_provider for what we're doing here
574 if key.param_env.reveal == Reveal::All {
575 let mut key = key.clone();
576 key.param_env.reveal = Reveal::UserFacing;
577 match tcx.const_eval(key) {
578 // try again with reveal all as requested
579 Err(ErrorHandled::TooGeneric) => {},
581 other => return other,
584 tcx.const_eval_raw(key).and_then(|val| {
585 validate_const(tcx, val, key)
589 pub fn const_eval_raw_provider<'a, 'tcx>(
590 tcx: TyCtxt<'a, 'tcx, 'tcx>,
591 key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
592 ) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
593 // Because the constant is computed twice (once per value of `Reveal`), we are at risk of
594 // reporting the same error twice here. To resolve this, we check whether we can evaluate the
595 // constant in the more restrictive `Reveal::UserFacing`, which most likely already was
596 // computed. For a large percentage of constants that will already have succeeded. Only
597 // associated constants of generic functions will fail due to not enough monomorphization
598 // information being available.
600 // In case we fail in the `UserFacing` variant, we just do the real computation.
601 if key.param_env.reveal == Reveal::All {
602 let mut key = key.clone();
603 key.param_env.reveal = Reveal::UserFacing;
604 match tcx.const_eval_raw(key) {
605 // try again with reveal all as requested
606 Err(ErrorHandled::TooGeneric) => {},
608 other => return other,
611 // the first trace is for replicating an ice
612 // There's no tracking issue, but the next two lines concatenated link to the discussion on
613 // zulip. It's not really possible to test this, because it doesn't show up in diagnostics
615 // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
616 // subject/anon_const_instance_printing/near/135980032
617 trace!("const eval: {}", key.value.instance);
618 trace!("const eval: {:?}", key);
621 let def_id = cid.instance.def.def_id();
623 if let Some(id) = tcx.hir.as_local_node_id(def_id) {
624 let tables = tcx.typeck_tables_of(def_id);
626 // Do match-check before building MIR
627 if let Err(ErrorReported) = tcx.check_match(def_id) {
628 return Err(ErrorHandled::Reported)
631 if let hir::BodyOwnerKind::Const = tcx.hir.body_owner_kind(id) {
632 tcx.mir_const_qualif(def_id);
635 // Do not continue into miri if typeck errors occurred; it will fail horribly
636 if tables.tainted_by_errors {
637 return Err(ErrorHandled::Reported)
641 let (res, ecx) = eval_body_and_ecx(tcx, cid, None, key.param_env);
643 let normalize = tcx.is_static(def_id).is_none() && cid.promoted.is_none();
645 // Sanity check: These must always be a MemPlace
647 Operand::Indirect(_) => { /* all is good */ },
648 Operand::Immediate(_) => bug!("const eval gave us an Immediate"),
651 op_to_const(&ecx, op, normalize)
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).is_some() {
656 let err = err.report_as_error(ecx.tcx, "could not evaluate static initializer");
657 // check that a static never produces `TooGeneric`
658 if tcx.sess.err_count() == 0 {
659 span_bug!(ecx.tcx.span, "static eval failure didn't emit an error: {:#?}", err);
662 } else if def_id.is_local() {
663 // constant defined in this crate, we can figure out a lint level!
664 match tcx.describe_def(def_id) {
665 // constants never produce a hard error at the definition site. Anything else is
666 // a backwards compatibility hazard (and will break old versions of winapi for sure)
668 // note that validation may still cause a hard error on this very same constant,
669 // because any code that existed before validation could not have failed validation
670 // thus preventing such a hard error from being a backwards compatibility hazard
671 Some(Def::Const(_)) | Some(Def::AssociatedConst(_)) => {
672 let node_id = tcx.hir.as_local_node_id(def_id).unwrap();
674 tcx.at(tcx.def_span(def_id)),
675 "any use of this value will cause an error",
679 // promoting runtime code is only allowed to error if it references broken constants
680 // any other kind of error will be reported to the user as a deny-by-default lint
681 _ => if let Some(p) = cid.promoted {
682 let span = tcx.optimized_mir(def_id).promoted[p].span;
683 if let EvalErrorKind::ReferencedConstant = err.error {
686 "evaluation of constant expression failed",
691 "reaching this expression at runtime will panic or abort",
692 tcx.hir.as_local_node_id(def_id).unwrap(),
695 // anything else (array lengths, enum initializers, constant patterns) are reported
700 "evaluation of constant value failed",
705 // use of broken constant from other crate
706 err.report_as_error(ecx.tcx, "could not evaluate constant")