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Auto merge of #67327 - oli-obk:cleanup, r=RalfJung

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Split up `const_eval.rs`

Fixes #67316

r? @RalfJung
This commit is contained in:
bors 2019-12-26 13:15:05 +00:00
commit 3ac40b69c7
7 changed files with 874 additions and 757 deletions
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729
src/librustc_mir/const_eval.rs
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@ -1,511 +1,25 @@
// Not in interpret to make sure we do not use private implementation details
use std::borrow::{Borrow, Cow};
use std::collections::hash_map::Entry;
use std::convert::TryInto;
use std::error::Error;
use std::fmt;
use std::hash::Hash;
use crate::interpret::eval_nullary_intrinsic;
use rustc::hir::def::DefKind;
use rustc::hir::def_id::DefId;
use rustc::mir;
use rustc::mir::interpret::{ConstEvalErr, ErrorHandled, ScalarMaybeUndef};
use rustc::traits::Reveal;
use rustc::ty::layout::{self, HasTyCtxt, LayoutOf, VariantIdx};
use rustc::ty::{self, subst::Subst, Ty, TyCtxt};
use rustc_data_structures::fx::FxHashMap;
use rustc::ty::layout::VariantIdx;
use rustc::ty::{self, TyCtxt};
use syntax::{
source_map::{Span, DUMMY_SP},
symbol::Symbol,
};
use syntax::{source_map::DUMMY_SP, symbol::Symbol};
use crate::interpret::{
self, intern_const_alloc_recursive, snapshot, AllocId, Allocation, AssertMessage, ConstValue,
GlobalId, ImmTy, Immediate, InterpCx, InterpErrorInfo, InterpResult, MPlaceTy, Machine, Memory,
MemoryKind, OpTy, PlaceTy, Pointer, RawConst, RefTracking, Scalar, StackPopCleanup,
};
use crate::interpret::{intern_const_alloc_recursive, ConstValue, InterpCx};
/// Number of steps until the detector even starts doing anything.
/// Also, a warning is shown to the user when this number is reached.
const STEPS_UNTIL_DETECTOR_ENABLED: isize = 1_000_000;
/// The number of steps between loop detector snapshots.
/// Should be a power of two for performance reasons.
const DETECTOR_SNAPSHOT_PERIOD: isize = 256;
mod error;
mod eval_queries;
mod machine;
/// The `InterpCx` is only meant to be used to do field and index projections into constants for
/// `simd_shuffle` and const patterns in match arms.
///
/// The function containing the `match` that is currently being analyzed may have generic bounds
/// that inform us about the generic bounds of the constant. E.g., using an associated constant
/// of a function's generic parameter will require knowledge about the bounds on the generic
/// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
fn mk_eval_cx<'mir, 'tcx>(
tcx: TyCtxt<'tcx>,
span: Span,
param_env: ty::ParamEnv<'tcx>,
can_access_statics: bool,
) -> CompileTimeEvalContext<'mir, 'tcx> {
debug!("mk_eval_cx: {:?}", param_env);
InterpCx::new(
tcx.at(span),
param_env,
CompileTimeInterpreter::new(),
MemoryExtra { can_access_statics },
)
}
fn op_to_const<'tcx>(
ecx: &CompileTimeEvalContext<'_, 'tcx>,
op: OpTy<'tcx>,
) -> &'tcx ty::Const<'tcx> {
// We do not have value optimizations for everything.
// Only scalars and slices, since they are very common.
// Note that further down we turn scalars of undefined bits back to `ByRef`. These can result
// from scalar unions that are initialized with one of their zero sized variants. We could
// instead allow `ConstValue::Scalar` to store `ScalarMaybeUndef`, but that would affect all
// the usual cases of extracting e.g. a `usize`, without there being a real use case for the
// `Undef` situation.
let try_as_immediate = match op.layout.abi {
layout::Abi::Scalar(..) => true,
layout::Abi::ScalarPair(..) => match op.layout.ty.kind {
ty::Ref(_, inner, _) => match inner.kind {
ty::Slice(elem) => elem == ecx.tcx.types.u8,
ty::Str => true,
_ => false,
},
_ => false,
},
_ => false,
};
let immediate = if try_as_immediate {
Err(ecx.read_immediate(op).expect("normalization works on validated constants"))
} else {
// It is guaranteed that any non-slice scalar pair is actually ByRef here.
// When we come back from raw const eval, we are always by-ref. The only way our op here is
// by-val is if we are in const_field, i.e., if this is (a field of) something that we
// "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
// structs containing such.
op.try_as_mplace()
};
let val = match immediate {
Ok(mplace) => {
let ptr = mplace.ptr.to_ptr().unwrap();
let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
ConstValue::ByRef { alloc, offset: ptr.offset }
}
// see comment on `let try_as_immediate` above
Err(ImmTy { imm: Immediate::Scalar(x), .. }) => match x {
ScalarMaybeUndef::Scalar(s) => ConstValue::Scalar(s),
ScalarMaybeUndef::Undef => {
// When coming out of "normal CTFE", we'll always have an `Indirect` operand as
// argument and we will not need this. The only way we can already have an
// `Immediate` is when we are called from `const_field`, and that `Immediate`
// comes from a constant so it can happen have `Undef`, because the indirect
// memory that was read had undefined bytes.
let mplace = op.assert_mem_place();
let ptr = mplace.ptr.to_ptr().unwrap();
let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
ConstValue::ByRef { alloc, offset: ptr.offset }
}
},
Err(ImmTy { imm: Immediate::ScalarPair(a, b), .. }) => {
let (data, start) = match a.not_undef().unwrap() {
Scalar::Ptr(ptr) => {
(ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id), ptr.offset.bytes())
}
Scalar::Raw { .. } => (
ecx.tcx.intern_const_alloc(Allocation::from_byte_aligned_bytes(b"" as &[u8])),
0,
),
};
let len = b.to_machine_usize(&ecx.tcx.tcx).unwrap();
let start = start.try_into().unwrap();
let len: usize = len.try_into().unwrap();
ConstValue::Slice { data, start, end: start + len }
}
};
ecx.tcx.mk_const(ty::Const { val: ty::ConstKind::Value(val), ty: op.layout.ty })
}
// Returns a pointer to where the result lives
fn eval_body_using_ecx<'mir, 'tcx>(
ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
cid: GlobalId<'tcx>,
body: &'mir mir::Body<'tcx>,
) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
debug!("eval_body_using_ecx: {:?}, {:?}", cid, ecx.param_env);
let tcx = ecx.tcx.tcx;
let layout = ecx.layout_of(body.return_ty().subst(tcx, cid.instance.substs))?;
assert!(!layout.is_unsized());
let ret = ecx.allocate(layout, MemoryKind::Stack);
let name = ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id()));
let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
// Assert all args (if any) are zero-sized types; `eval_body_using_ecx` doesn't
// make sense if the body is expecting nontrivial arguments.
// (The alternative would be to use `eval_fn_call` with an args slice.)
for arg in body.args_iter() {
let decl = body.local_decls.get(arg).expect("arg missing from local_decls");
let layout = ecx.layout_of(decl.ty.subst(tcx, cid.instance.substs))?;
assert!(layout.is_zst())
}
ecx.push_stack_frame(
cid.instance,
body.span,
body,
Some(ret.into()),
StackPopCleanup::None { cleanup: false },
)?;
// The main interpreter loop.
ecx.run()?;
// Intern the result
intern_const_alloc_recursive(ecx, tcx.static_mutability(cid.instance.def_id()), ret)?;
debug!("eval_body_using_ecx done: {:?}", *ret);
Ok(ret)
}
#[derive(Clone, Debug)]
pub enum ConstEvalError {
NeedsRfc(String),
ConstAccessesStatic,
}
impl<'tcx> Into<InterpErrorInfo<'tcx>> for ConstEvalError {
fn into(self) -> InterpErrorInfo<'tcx> {
err_unsup!(Unsupported(self.to_string())).into()
}
}
impl fmt::Display for ConstEvalError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
use self::ConstEvalError::*;
match *self {
NeedsRfc(ref msg) => {
write!(f, "\"{}\" needs an rfc before being allowed inside constants", msg)
}
ConstAccessesStatic => write!(f, "constant accesses static"),
}
}
}
impl Error for ConstEvalError {}
// Extra machine state for CTFE, and the Machine instance
pub struct CompileTimeInterpreter<'mir, 'tcx> {
/// When this value is negative, it indicates the number of interpreter
/// steps *until* the loop detector is enabled. When it is positive, it is
/// the number of steps after the detector has been enabled modulo the loop
/// detector period.
pub(super) steps_since_detector_enabled: isize,
/// Extra state to detect loops.
pub(super) loop_detector: snapshot::InfiniteLoopDetector<'mir, 'tcx>,
}
#[derive(Copy, Clone, Debug)]
pub struct MemoryExtra {
/// Whether this machine may read from statics
can_access_statics: bool,
}
impl<'mir, 'tcx> CompileTimeInterpreter<'mir, 'tcx> {
fn new() -> Self {
CompileTimeInterpreter {
loop_detector: Default::default(),
steps_since_detector_enabled: -STEPS_UNTIL_DETECTOR_ENABLED,
}
}
}
impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
#[inline(always)]
fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
where
K: Borrow<Q>,
{
FxHashMap::contains_key(self, k)
}
#[inline(always)]
fn insert(&mut self, k: K, v: V) -> Option<V> {
FxHashMap::insert(self, k, v)
}
#[inline(always)]
fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
where
K: Borrow<Q>,
{
FxHashMap::remove(self, k)
}
#[inline(always)]
fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
self.iter().filter_map(move |(k, v)| f(k, &*v)).collect()
}
#[inline(always)]
fn get_or<E>(&self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&V, E> {
match self.get(&k) {
Some(v) => Ok(v),
None => {
vacant()?;
bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
}
}
}
#[inline(always)]
fn get_mut_or<E>(&mut self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&mut V, E> {
match self.entry(k) {
Entry::Occupied(e) => Ok(e.into_mut()),
Entry::Vacant(e) => {
let v = vacant()?;
Ok(e.insert(v))
}
}
}
}
crate type CompileTimeEvalContext<'mir, 'tcx> =
InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>;
impl interpret::MayLeak for ! {
#[inline(always)]
fn may_leak(self) -> bool {
// `self` is uninhabited
self
}
}
impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir, 'tcx> {
type MemoryKinds = !;
type PointerTag = ();
type ExtraFnVal = !;
type FrameExtra = ();
type MemoryExtra = MemoryExtra;
type AllocExtra = ();
type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
const STATIC_KIND: Option<!> = None; // no copying of statics allowed
// We do not check for alignment to avoid having to carry an `Align`
// in `ConstValue::ByRef`.
const CHECK_ALIGN: bool = false;
#[inline(always)]
fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
false // for now, we don't enforce validity
}
fn find_mir_or_eval_fn(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
instance: ty::Instance<'tcx>,
args: &[OpTy<'tcx>],
ret: Option<(PlaceTy<'tcx>, mir::BasicBlock)>,
_unwind: Option<mir::BasicBlock>, // unwinding is not supported in consts
) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>> {
debug!("find_mir_or_eval_fn: {:?}", instance);
// Only check non-glue functions
if let ty::InstanceDef::Item(def_id) = instance.def {
// Execution might have wandered off into other crates, so we cannot do a stability-
// sensitive check here. But we can at least rule out functions that are not const
// at all.
if ecx.tcx.is_const_fn_raw(def_id) {
// If this function is a `const fn` then as an optimization we can query this
// evaluation immediately.
//
// For the moment we only do this for functions which take no arguments
// (or all arguments are ZSTs) so that we don't memoize too much.
//
// Because `#[track_caller]` adds an implicit non-ZST argument, we also cannot
// perform this optimization on items tagged with it.
let no_implicit_args = !instance.def.requires_caller_location(ecx.tcx());
if args.iter().all(|a| a.layout.is_zst()) && no_implicit_args {
let gid = GlobalId { instance, promoted: None };
ecx.eval_const_fn_call(gid, ret)?;
return Ok(None);
}
} else {
// Some functions we support even if they are non-const -- but avoid testing
// that for const fn! We certainly do *not* want to actually call the fn
// though, so be sure we return here.
return if ecx.hook_panic_fn(instance, args, ret)? {
Ok(None)
} else {
throw_unsup_format!("calling non-const function `{}`", instance)
};
}
}
// This is a const fn. Call it.
Ok(Some(match ecx.load_mir(instance.def, None) {
Ok(body) => *body,
Err(err) => {
if let err_unsup!(NoMirFor(ref path)) = err.kind {
return Err(ConstEvalError::NeedsRfc(format!(
"calling extern function `{}`",
path
))
.into());
}
return Err(err);
}
}))
}
fn call_extra_fn(
_ecx: &mut InterpCx<'mir, 'tcx, Self>,
fn_val: !,
_args: &[OpTy<'tcx>],
_ret: Option<(PlaceTy<'tcx>, mir::BasicBlock)>,
_unwind: Option<mir::BasicBlock>,
) -> InterpResult<'tcx> {
match fn_val {}
}
fn call_intrinsic(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
span: Span,
instance: ty::Instance<'tcx>,
args: &[OpTy<'tcx>],
ret: Option<(PlaceTy<'tcx>, mir::BasicBlock)>,
_unwind: Option<mir::BasicBlock>,
) -> InterpResult<'tcx> {
if ecx.emulate_intrinsic(span, instance, args, ret)? {
return Ok(());
}
// An intrinsic that we do not support
let intrinsic_name = ecx.tcx.item_name(instance.def_id());
Err(ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into())
}
fn assert_panic(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
_span: Span,
msg: &AssertMessage<'tcx>,
_unwind: Option<mir::BasicBlock>,
) -> InterpResult<'tcx> {
use rustc::mir::interpret::PanicInfo::*;
Err(match msg {
BoundsCheck { ref len, ref index } => {
let len = ecx
.read_immediate(ecx.eval_operand(len, None)?)
.expect("can't eval len")
.to_scalar()?
.to_machine_usize(&*ecx)?;
let index = ecx
.read_immediate(ecx.eval_operand(index, None)?)
.expect("can't eval index")
.to_scalar()?
.to_machine_usize(&*ecx)?;
err_panic!(BoundsCheck { len, index })
}
Overflow(op) => err_panic!(Overflow(*op)),
OverflowNeg => err_panic!(OverflowNeg),
DivisionByZero => err_panic!(DivisionByZero),
RemainderByZero => err_panic!(RemainderByZero),
ResumedAfterReturn(generator_kind) => err_panic!(ResumedAfterReturn(*generator_kind)),
ResumedAfterPanic(generator_kind) => err_panic!(ResumedAfterPanic(*generator_kind)),
Panic { .. } => bug!("`Panic` variant cannot occur in MIR"),
}
.into())
}
fn ptr_to_int(_mem: &Memory<'mir, 'tcx, Self>, _ptr: Pointer) -> InterpResult<'tcx, u64> {
Err(ConstEvalError::NeedsRfc("pointer-to-integer cast".to_string()).into())
}
fn binary_ptr_op(
_ecx: &InterpCx<'mir, 'tcx, Self>,
_bin_op: mir::BinOp,
_left: ImmTy<'tcx>,
_right: ImmTy<'tcx>,
) -> InterpResult<'tcx, (Scalar, bool, Ty<'tcx>)> {
Err(ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into())
}
fn find_foreign_static(
_tcx: TyCtxt<'tcx>,
_def_id: DefId,
) -> InterpResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> {
throw_unsup!(ReadForeignStatic)
}
#[inline(always)]
fn init_allocation_extra<'b>(
_memory_extra: &MemoryExtra,
_id: AllocId,
alloc: Cow<'b, Allocation>,
_kind: Option<MemoryKind<!>>,
) -> (Cow<'b, Allocation<Self::PointerTag>>, Self::PointerTag) {
// We do not use a tag so we can just cheaply forward the allocation
(alloc, ())
}
#[inline(always)]
fn tag_static_base_pointer(_memory_extra: &MemoryExtra, _id: AllocId) -> Self::PointerTag {
()
}
fn box_alloc(
_ecx: &mut InterpCx<'mir, 'tcx, Self>,
_dest: PlaceTy<'tcx>,
) -> InterpResult<'tcx> {
Err(ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into())
}
fn before_terminator(ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
{
let steps = &mut ecx.machine.steps_since_detector_enabled;
*steps += 1;
if *steps < 0 {
return Ok(());
}
*steps %= DETECTOR_SNAPSHOT_PERIOD;
if *steps != 0 {
return Ok(());
}
}
let span = ecx.frame().span;
ecx.machine.loop_detector.observe_and_analyze(*ecx.tcx, span, &ecx.memory, &ecx.stack[..])
}
#[inline(always)]
fn stack_push(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
Ok(())
}
fn before_access_static(
memory_extra: &MemoryExtra,
_allocation: &Allocation,
) -> InterpResult<'tcx> {
if memory_extra.can_access_statics {
Ok(())
} else {
Err(ConstEvalError::ConstAccessesStatic.into())
}
}
}
pub use error::*;
pub use eval_queries::*;
pub use machine::*;
/// Extracts a field of a (variant of a) const.
// this function uses `unwrap` copiously, because an already validated constant must have valid
// fields and can thus never fail outside of compiler bugs
pub fn const_field<'tcx>(
pub(crate) fn const_field<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
variant: Option<VariantIdx>,
@ -528,7 +42,7 @@ pub fn const_field<'tcx>(
op_to_const(&ecx, field)
}
pub fn const_caller_location<'tcx>(
pub(crate) fn const_caller_location<'tcx>(
tcx: TyCtxt<'tcx>,
(file, line, col): (Symbol, u32, u32),
) -> &'tcx ty::Const<'tcx> {
@ -548,7 +62,7 @@ pub fn const_caller_location<'tcx>(
// this function uses `unwrap` copiously, because an already validated constant must have valid
// fields and can thus never fail outside of compiler bugs
pub fn const_variant_index<'tcx>(
pub(crate) fn const_variant_index<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
val: &'tcx ty::Const<'tcx>,
@ -558,220 +72,3 @@ pub fn const_variant_index<'tcx>(
let op = ecx.eval_const_to_op(val, None).unwrap();
ecx.read_discriminant(op).unwrap().1
}
/// Turn an interpreter error into something to report to the user.
/// As a side-effect, if RUSTC_CTFE_BACKTRACE is set, this prints the backtrace.
/// Should be called only if the error is actually going to to be reported!
pub fn error_to_const_error<'mir, 'tcx, M: Machine<'mir, 'tcx>>(
ecx: &InterpCx<'mir, 'tcx, M>,
mut error: InterpErrorInfo<'tcx>,
) -> ConstEvalErr<'tcx> {
error.print_backtrace();
let stacktrace = ecx.generate_stacktrace(None);
ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
}
pub fn note_on_undefined_behavior_error() -> &'static str {
"The rules on what exactly is undefined behavior aren't clear, \
so this check might be overzealous. Please open an issue on the rustc \
repository if you believe it should not be considered undefined behavior."
}
fn validate_and_turn_into_const<'tcx>(
tcx: TyCtxt<'tcx>,
constant: RawConst<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
let cid = key.value;
let def_id = cid.instance.def.def_id();
let is_static = tcx.is_static(def_id);
let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
let val = (|| {
let mplace = ecx.raw_const_to_mplace(constant)?;
let mut ref_tracking = RefTracking::new(mplace);
while let Some((mplace, path)) = ref_tracking.todo.pop() {
ecx.validate_operand(mplace.into(), path, Some(&mut ref_tracking))?;
}
// Now that we validated, turn this into a proper constant.
// Statics/promoteds are always `ByRef`, for the rest `op_to_const` decides
// whether they become immediates.
if is_static || cid.promoted.is_some() {
let ptr = mplace.ptr.to_ptr()?;
Ok(tcx.mk_const(ty::Const {
val: ty::ConstKind::Value(ConstValue::ByRef {
alloc: ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id),
offset: ptr.offset,
}),
ty: mplace.layout.ty,
}))
} else {
Ok(op_to_const(&ecx, mplace.into()))
}
})();
val.map_err(|error| {
let err = error_to_const_error(&ecx, error);
match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
Ok(mut diag) => {
diag.note(note_on_undefined_behavior_error());
diag.emit();
ErrorHandled::Reported
}
Err(err) => err,
}
})
}
pub fn const_eval_validated_provider<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
// see comment in const_eval_raw_provider for what we're doing here
if key.param_env.reveal == Reveal::All {
let mut key = key.clone();
key.param_env.reveal = Reveal::UserFacing;
match tcx.const_eval_validated(key) {
// try again with reveal all as requested
Err(ErrorHandled::TooGeneric) => {
// Promoteds should never be "too generic" when getting evaluated.
// They either don't get evaluated, or we are in a monomorphic context
assert!(key.value.promoted.is_none());
}
// dedupliate calls
other => return other,
}
}
// We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
// Catch such calls and evaluate them instead of trying to load a constant's MIR.
if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
let ty = key.value.instance.ty(tcx);
let substs = match ty.kind {
ty::FnDef(_, substs) => substs,
_ => bug!("intrinsic with type {:?}", ty),
};
return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
let span = tcx.def_span(def_id);
let error = ConstEvalErr { error: error.kind, stacktrace: vec![], span };
error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
});
}
tcx.const_eval_raw(key).and_then(|val| validate_and_turn_into_const(tcx, val, key))
}
pub fn const_eval_raw_provider<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
// Because the constant is computed twice (once per value of `Reveal`), we are at risk of
// reporting the same error twice here. To resolve this, we check whether we can evaluate the
// constant in the more restrictive `Reveal::UserFacing`, which most likely already was
// computed. For a large percentage of constants that will already have succeeded. Only
// associated constants of generic functions will fail due to not enough monomorphization
// information being available.
// In case we fail in the `UserFacing` variant, we just do the real computation.
if key.param_env.reveal == Reveal::All {
let mut key = key.clone();
key.param_env.reveal = Reveal::UserFacing;
match tcx.const_eval_raw(key) {
// try again with reveal all as requested
Err(ErrorHandled::TooGeneric) => {}
// dedupliate calls
other => return other,
}
}
if cfg!(debug_assertions) {
// Make sure we format the instance even if we do not print it.
// This serves as a regression test against an ICE on printing.
// The next two lines concatenated contain some discussion:
// https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
// subject/anon_const_instance_printing/near/135980032
let instance = key.value.instance.to_string();
trace!("const eval: {:?} ({})", key, instance);
}
let cid = key.value;
let def_id = cid.instance.def.def_id();
if def_id.is_local() && tcx.typeck_tables_of(def_id).tainted_by_errors {
return Err(ErrorHandled::Reported);
}
let is_static = tcx.is_static(def_id);
let span = tcx.def_span(cid.instance.def_id());
let mut ecx = InterpCx::new(
tcx.at(span),
key.param_env,
CompileTimeInterpreter::new(),
MemoryExtra { can_access_statics: is_static },
);
let res = ecx.load_mir(cid.instance.def, cid.promoted);
res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, *body))
.and_then(|place| {
Ok(RawConst { alloc_id: place.ptr.assert_ptr().alloc_id, ty: place.layout.ty })
})
.map_err(|error| {
let err = error_to_const_error(&ecx, error);
// errors in statics are always emitted as fatal errors
if is_static {
// Ensure that if the above error was either `TooGeneric` or `Reported`
// an error must be reported.
let v = err.report_as_error(ecx.tcx, "could not evaluate static initializer");
tcx.sess.delay_span_bug(
err.span,
&format!("static eval failure did not emit an error: {:#?}", v),
);
v
} else if def_id.is_local() {
// constant defined in this crate, we can figure out a lint level!
match tcx.def_kind(def_id) {
// constants never produce a hard error at the definition site. Anything else is
// a backwards compatibility hazard (and will break old versions of winapi for sure)
//
// note that validation may still cause a hard error on this very same constant,
// because any code that existed before validation could not have failed validation
// thus preventing such a hard error from being a backwards compatibility hazard
Some(DefKind::Const) | Some(DefKind::AssocConst) => {
let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
err.report_as_lint(
tcx.at(tcx.def_span(def_id)),
"any use of this value will cause an error",
hir_id,
Some(err.span),
)
}
// promoting runtime code is only allowed to error if it references broken constants
// any other kind of error will be reported to the user as a deny-by-default lint
_ => {
if let Some(p) = cid.promoted {
let span = tcx.promoted_mir(def_id)[p].span;
if let err_inval!(ReferencedConstant) = err.error {
err.report_as_error(
tcx.at(span),
"evaluation of constant expression failed",
)
} else {
err.report_as_lint(
tcx.at(span),
"reaching this expression at runtime will panic or abort",
tcx.hir().as_local_hir_id(def_id).unwrap(),
Some(err.span),
)
}
// anything else (array lengths, enum initializers, constant patterns) are reported
// as hard errors
} else {
err.report_as_error(ecx.tcx, "evaluation of constant value failed")
}
}
}
} else {
// use of broken constant from other crate
err.report_as_error(ecx.tcx, "could not evaluate constant")
}
})
}

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use std::error::Error;
use std::fmt;
use super::InterpCx;
use crate::interpret::{ConstEvalErr, InterpErrorInfo, Machine};
#[derive(Clone, Debug)]
pub enum ConstEvalError {
NeedsRfc(String),
ConstAccessesStatic,
}
impl<'tcx> Into<InterpErrorInfo<'tcx>> for ConstEvalError {
fn into(self) -> InterpErrorInfo<'tcx> {
err_unsup!(Unsupported(self.to_string())).into()
}
}
impl fmt::Display for ConstEvalError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
use self::ConstEvalError::*;
match *self {
NeedsRfc(ref msg) => {
write!(f, "\"{}\" needs an rfc before being allowed inside constants", msg)
}
ConstAccessesStatic => write!(f, "constant accesses static"),
}
}
}
impl Error for ConstEvalError {}
/// Turn an interpreter error into something to report to the user.
/// As a side-effect, if RUSTC_CTFE_BACKTRACE is set, this prints the backtrace.
/// Should be called only if the error is actually going to to be reported!
pub fn error_to_const_error<'mir, 'tcx, M: Machine<'mir, 'tcx>>(
ecx: &InterpCx<'mir, 'tcx, M>,
mut error: InterpErrorInfo<'tcx>,
) -> ConstEvalErr<'tcx> {
error.print_backtrace();
let stacktrace = ecx.generate_stacktrace(None);
ConstEvalErr { error: error.kind, stacktrace, span: ecx.tcx.span }
}

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use super::{error_to_const_error, CompileTimeEvalContext, CompileTimeInterpreter, MemoryExtra};
use crate::interpret::eval_nullary_intrinsic;
use crate::interpret::{
intern_const_alloc_recursive, Allocation, ConstValue, GlobalId, ImmTy, Immediate, InterpCx,
InterpResult, MPlaceTy, MemoryKind, OpTy, RawConst, RefTracking, Scalar, ScalarMaybeUndef,
StackPopCleanup,
};
use rustc::hir::def::DefKind;
use rustc::mir;
use rustc::mir::interpret::{ConstEvalErr, ErrorHandled};
use rustc::traits::Reveal;
use rustc::ty::{self, layout, layout::LayoutOf, subst::Subst, TyCtxt};
use std::convert::TryInto;
use syntax::source_map::Span;
pub fn note_on_undefined_behavior_error() -> &'static str {
"The rules on what exactly is undefined behavior aren't clear, \
so this check might be overzealous. Please open an issue on the rustc \
repository if you believe it should not be considered undefined behavior."
}
// Returns a pointer to where the result lives
fn eval_body_using_ecx<'mir, 'tcx>(
ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
cid: GlobalId<'tcx>,
body: &'mir mir::Body<'tcx>,
) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
debug!("eval_body_using_ecx: {:?}, {:?}", cid, ecx.param_env);
let tcx = ecx.tcx.tcx;
let layout = ecx.layout_of(body.return_ty().subst(tcx, cid.instance.substs))?;
assert!(!layout.is_unsized());
let ret = ecx.allocate(layout, MemoryKind::Stack);
let name = ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id()));
let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
// Assert all args (if any) are zero-sized types; `eval_body_using_ecx` doesn't
// make sense if the body is expecting nontrivial arguments.
// (The alternative would be to use `eval_fn_call` with an args slice.)
for arg in body.args_iter() {
let decl = body.local_decls.get(arg).expect("arg missing from local_decls");
let layout = ecx.layout_of(decl.ty.subst(tcx, cid.instance.substs))?;
assert!(layout.is_zst())
}
ecx.push_stack_frame(
cid.instance,
body.span,
body,
Some(ret.into()),
StackPopCleanup::None { cleanup: false },
)?;
// The main interpreter loop.
ecx.run()?;
// Intern the result
intern_const_alloc_recursive(ecx, tcx.static_mutability(cid.instance.def_id()), ret)?;
debug!("eval_body_using_ecx done: {:?}", *ret);
Ok(ret)
}
/// The `InterpCx` is only meant to be used to do field and index projections into constants for
/// `simd_shuffle` and const patterns in match arms.
///
/// The function containing the `match` that is currently being analyzed may have generic bounds
/// that inform us about the generic bounds of the constant. E.g., using an associated constant
/// of a function's generic parameter will require knowledge about the bounds on the generic
/// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
pub(super) fn mk_eval_cx<'mir, 'tcx>(
tcx: TyCtxt<'tcx>,
span: Span,
param_env: ty::ParamEnv<'tcx>,
can_access_statics: bool,
) -> CompileTimeEvalContext<'mir, 'tcx> {
debug!("mk_eval_cx: {:?}", param_env);
InterpCx::new(
tcx.at(span),
param_env,
CompileTimeInterpreter::new(),
MemoryExtra { can_access_statics },
)
}
pub(super) fn op_to_const<'tcx>(
ecx: &CompileTimeEvalContext<'_, 'tcx>,
op: OpTy<'tcx>,
) -> &'tcx ty::Const<'tcx> {
// We do not have value optimizations for everything.
// Only scalars and slices, since they are very common.
// Note that further down we turn scalars of undefined bits back to `ByRef`. These can result
// from scalar unions that are initialized with one of their zero sized variants. We could
// instead allow `ConstValue::Scalar` to store `ScalarMaybeUndef`, but that would affect all
// the usual cases of extracting e.g. a `usize`, without there being a real use case for the
// `Undef` situation.
let try_as_immediate = match op.layout.abi {
layout::Abi::Scalar(..) => true,
layout::Abi::ScalarPair(..) => match op.layout.ty.kind {
ty::Ref(_, inner, _) => match inner.kind {
ty::Slice(elem) => elem == ecx.tcx.types.u8,
ty::Str => true,
_ => false,
},
_ => false,
},
_ => false,
};
let immediate = if try_as_immediate {
Err(ecx.read_immediate(op).expect("normalization works on validated constants"))
} else {
// It is guaranteed that any non-slice scalar pair is actually ByRef here.
// When we come back from raw const eval, we are always by-ref. The only way our op here is
// by-val is if we are in const_field, i.e., if this is (a field of) something that we
// "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
// structs containing such.
op.try_as_mplace()
};
let val = match immediate {
Ok(mplace) => {
let ptr = mplace.ptr.to_ptr().unwrap();
let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
ConstValue::ByRef { alloc, offset: ptr.offset }
}
// see comment on `let try_as_immediate` above
Err(ImmTy { imm: Immediate::Scalar(x), .. }) => match x {
ScalarMaybeUndef::Scalar(s) => ConstValue::Scalar(s),
ScalarMaybeUndef::Undef => {
// When coming out of "normal CTFE", we'll always have an `Indirect` operand as
// argument and we will not need this. The only way we can already have an
// `Immediate` is when we are called from `const_field`, and that `Immediate`
// comes from a constant so it can happen have `Undef`, because the indirect
// memory that was read had undefined bytes.
let mplace = op.assert_mem_place();
let ptr = mplace.ptr.to_ptr().unwrap();
let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
ConstValue::ByRef { alloc, offset: ptr.offset }
}
},
Err(ImmTy { imm: Immediate::ScalarPair(a, b), .. }) => {
let (data, start) = match a.not_undef().unwrap() {
Scalar::Ptr(ptr) => {
(ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id), ptr.offset.bytes())
}
Scalar::Raw { .. } => (
ecx.tcx.intern_const_alloc(Allocation::from_byte_aligned_bytes(b"" as &[u8])),
0,
),
};
let len = b.to_machine_usize(&ecx.tcx.tcx).unwrap();
let start = start.try_into().unwrap();
let len: usize = len.try_into().unwrap();
ConstValue::Slice { data, start, end: start + len }
}
};
ecx.tcx.mk_const(ty::Const { val: ty::ConstKind::Value(val), ty: op.layout.ty })
}
fn validate_and_turn_into_const<'tcx>(
tcx: TyCtxt<'tcx>,
constant: RawConst<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
let cid = key.value;
let def_id = cid.instance.def.def_id();
let is_static = tcx.is_static(def_id);
let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
let val = (|| {
let mplace = ecx.raw_const_to_mplace(constant)?;
let mut ref_tracking = RefTracking::new(mplace);
while let Some((mplace, path)) = ref_tracking.todo.pop() {
ecx.validate_operand(mplace.into(), path, Some(&mut ref_tracking))?;
}
// Now that we validated, turn this into a proper constant.
// Statics/promoteds are always `ByRef`, for the rest `op_to_const` decides
// whether they become immediates.
if is_static || cid.promoted.is_some() {
let ptr = mplace.ptr.to_ptr()?;
Ok(tcx.mk_const(ty::Const {
val: ty::ConstKind::Value(ConstValue::ByRef {
alloc: ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id),
offset: ptr.offset,
}),
ty: mplace.layout.ty,
}))
} else {
Ok(op_to_const(&ecx, mplace.into()))
}
})();
val.map_err(|error| {
let err = error_to_const_error(&ecx, error);
match err.struct_error(ecx.tcx, "it is undefined behavior to use this value") {
Ok(mut diag) => {
diag.note(note_on_undefined_behavior_error());
diag.emit();
ErrorHandled::Reported
}
Err(err) => err,
}
})
}
pub fn const_eval_validated_provider<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
// see comment in const_eval_raw_provider for what we're doing here
if key.param_env.reveal == Reveal::All {
let mut key = key.clone();
key.param_env.reveal = Reveal::UserFacing;
match tcx.const_eval_validated(key) {
// try again with reveal all as requested
Err(ErrorHandled::TooGeneric) => {
// Promoteds should never be "too generic" when getting evaluated.
// They either don't get evaluated, or we are in a monomorphic context
assert!(key.value.promoted.is_none());
}
// dedupliate calls
other => return other,
}
}
// We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
// Catch such calls and evaluate them instead of trying to load a constant's MIR.
if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
let ty = key.value.instance.ty(tcx);
let substs = match ty.kind {
ty::FnDef(_, substs) => substs,
_ => bug!("intrinsic with type {:?}", ty),
};
return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
let span = tcx.def_span(def_id);
let error = ConstEvalErr { error: error.kind, stacktrace: vec![], span };
error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
});
}
tcx.const_eval_raw(key).and_then(|val| validate_and_turn_into_const(tcx, val, key))
}
pub fn const_eval_raw_provider<'tcx>(
tcx: TyCtxt<'tcx>,
key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
// Because the constant is computed twice (once per value of `Reveal`), we are at risk of
// reporting the same error twice here. To resolve this, we check whether we can evaluate the
// constant in the more restrictive `Reveal::UserFacing`, which most likely already was
// computed. For a large percentage of constants that will already have succeeded. Only
// associated constants of generic functions will fail due to not enough monomorphization
// information being available.
// In case we fail in the `UserFacing` variant, we just do the real computation.
if key.param_env.reveal == Reveal::All {
let mut key = key.clone();
key.param_env.reveal = Reveal::UserFacing;
match tcx.const_eval_raw(key) {
// try again with reveal all as requested
Err(ErrorHandled::TooGeneric) => {}
// dedupliate calls
other => return other,
}
}
if cfg!(debug_assertions) {
// Make sure we format the instance even if we do not print it.
// This serves as a regression test against an ICE on printing.
// The next two lines concatenated contain some discussion:
// https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
// subject/anon_const_instance_printing/near/135980032
let instance = key.value.instance.to_string();
trace!("const eval: {:?} ({})", key, instance);
}
let cid = key.value;
let def_id = cid.instance.def.def_id();
if def_id.is_local() && tcx.typeck_tables_of(def_id).tainted_by_errors {
return Err(ErrorHandled::Reported);
}
let is_static = tcx.is_static(def_id);
let span = tcx.def_span(cid.instance.def_id());
let mut ecx = InterpCx::new(
tcx.at(span),
key.param_env,
CompileTimeInterpreter::new(),
MemoryExtra { can_access_statics: is_static },
);
let res = ecx.load_mir(cid.instance.def, cid.promoted);
res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, *body))
.and_then(|place| {
Ok(RawConst { alloc_id: place.ptr.assert_ptr().alloc_id, ty: place.layout.ty })
})
.map_err(|error| {
let err = error_to_const_error(&ecx, error);
// errors in statics are always emitted as fatal errors
if is_static {
// Ensure that if the above error was either `TooGeneric` or `Reported`
// an error must be reported.
let v = err.report_as_error(ecx.tcx, "could not evaluate static initializer");
tcx.sess.delay_span_bug(
err.span,
&format!("static eval failure did not emit an error: {:#?}", v),
);
v
} else if def_id.is_local() {
// constant defined in this crate, we can figure out a lint level!
match tcx.def_kind(def_id) {
// constants never produce a hard error at the definition site. Anything else is
// a backwards compatibility hazard (and will break old versions of winapi for
// sure)
//
// note that validation may still cause a hard error on this very same constant,
// because any code that existed before validation could not have failed
// validation thus preventing such a hard error from being a backwards
// compatibility hazard
Some(DefKind::Const) | Some(DefKind::AssocConst) => {
let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
err.report_as_lint(
tcx.at(tcx.def_span(def_id)),
"any use of this value will cause an error",
hir_id,
Some(err.span),
)
}
// promoting runtime code is only allowed to error if it references broken
// constants any other kind of error will be reported to the user as a
// deny-by-default lint
_ => {
if let Some(p) = cid.promoted {
let span = tcx.promoted_mir(def_id)[p].span;
if let err_inval!(ReferencedConstant) = err.error {
err.report_as_error(
tcx.at(span),
"evaluation of constant expression failed",
)
} else {
err.report_as_lint(
tcx.at(span),
"reaching this expression at runtime will panic or abort",
tcx.hir().as_local_hir_id(def_id).unwrap(),
Some(err.span),
)
}
// anything else (array lengths, enum initializers, constant patterns) are
// reported as hard errors
} else {
err.report_as_error(ecx.tcx, "evaluation of constant value failed")
}
}
}
} else {
// use of broken constant from other crate
err.report_as_error(ecx.tcx, "could not evaluate constant")
}
})
}

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use rustc::hir::def_id::DefId;
use rustc::mir;
use rustc::ty::layout::HasTyCtxt;
use rustc::ty::{self, Ty, TyCtxt};
use std::borrow::{Borrow, Cow};
use std::collections::hash_map::Entry;
use std::hash::Hash;
use rustc_data_structures::fx::FxHashMap;
use syntax::source_map::Span;
use crate::interpret::{
self, snapshot, AllocId, Allocation, AssertMessage, GlobalId, ImmTy, InterpCx, InterpResult,
Memory, MemoryKind, OpTy, PlaceTy, Pointer, Scalar,
};
use super::error::*;
impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> {
/// Evaluate a const function where all arguments (if any) are zero-sized types.
/// The evaluation is memoized thanks to the query system.
///
/// Returns `true` if the call has been evaluated.
fn try_eval_const_fn_call(
&mut self,
instance: ty::Instance<'tcx>,
ret: Option<(PlaceTy<'tcx>, mir::BasicBlock)>,
args: &[OpTy<'tcx>],
) -> InterpResult<'tcx, bool> {
trace!("try_eval_const_fn_call: {:?}", instance);
// Because `#[track_caller]` adds an implicit non-ZST argument, we also cannot
// perform this optimization on items tagged with it.
if instance.def.requires_caller_location(self.tcx()) {
return Ok(false);
}
// For the moment we only do this for functions which take no arguments
// (or all arguments are ZSTs) so that we don't memoize too much.
if args.iter().any(|a| !a.layout.is_zst()) {
return Ok(false);
}
let dest = match ret {
Some((dest, _)) => dest,
// Don't memoize diverging function calls.
None => return Ok(false),
};
let gid = GlobalId { instance, promoted: None };
let place = self.const_eval_raw(gid)?;
self.copy_op(place.into(), dest)?;
self.return_to_block(ret.map(|r| r.1))?;
self.dump_place(*dest);
return Ok(true);
}
}
/// Number of steps until the detector even starts doing anything.
/// Also, a warning is shown to the user when this number is reached.
const STEPS_UNTIL_DETECTOR_ENABLED: isize = 1_000_000;
/// The number of steps between loop detector snapshots.
/// Should be a power of two for performance reasons.
const DETECTOR_SNAPSHOT_PERIOD: isize = 256;
// Extra machine state for CTFE, and the Machine instance
pub struct CompileTimeInterpreter<'mir, 'tcx> {
/// When this value is negative, it indicates the number of interpreter
/// steps *until* the loop detector is enabled. When it is positive, it is
/// the number of steps after the detector has been enabled modulo the loop
/// detector period.
pub(super) steps_since_detector_enabled: isize,
/// Extra state to detect loops.
pub(super) loop_detector: snapshot::InfiniteLoopDetector<'mir, 'tcx>,
}
#[derive(Copy, Clone, Debug)]
pub struct MemoryExtra {
/// Whether this machine may read from statics
pub(super) can_access_statics: bool,
}
impl<'mir, 'tcx> CompileTimeInterpreter<'mir, 'tcx> {
pub(super) fn new() -> Self {
CompileTimeInterpreter {
loop_detector: Default::default(),
steps_since_detector_enabled: -STEPS_UNTIL_DETECTOR_ENABLED,
}
}
}
impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxHashMap<K, V> {
#[inline(always)]
fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
where
K: Borrow<Q>,
{
FxHashMap::contains_key(self, k)
}
#[inline(always)]
fn insert(&mut self, k: K, v: V) -> Option<V> {
FxHashMap::insert(self, k, v)
}
#[inline(always)]
fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
where
K: Borrow<Q>,
{
FxHashMap::remove(self, k)
}
#[inline(always)]
fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
self.iter().filter_map(move |(k, v)| f(k, &*v)).collect()
}
#[inline(always)]
fn get_or<E>(&self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&V, E> {
match self.get(&k) {
Some(v) => Ok(v),
None => {
vacant()?;
bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
}
}
}
#[inline(always)]
fn get_mut_or<E>(&mut self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&mut V, E> {
match self.entry(k) {
Entry::Occupied(e) => Ok(e.into_mut()),
Entry::Vacant(e) => {
let v = vacant()?;
Ok(e.insert(v))
}
}
}
}
crate type CompileTimeEvalContext<'mir, 'tcx> =
InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>;
impl interpret::MayLeak for ! {
#[inline(always)]
fn may_leak(self) -> bool {
// `self` is uninhabited
self
}
}
impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir, 'tcx> {
type MemoryKinds = !;
type PointerTag = ();
type ExtraFnVal = !;
type FrameExtra = ();
type MemoryExtra = MemoryExtra;
type AllocExtra = ();
type MemoryMap = FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
const STATIC_KIND: Option<!> = None; // no copying of statics allowed
// We do not check for alignment to avoid having to carry an `Align`
// in `ConstValue::ByRef`.
const CHECK_ALIGN: bool = false;
#[inline(always)]
fn enforce_validity(_ecx: &InterpCx<'mir, 'tcx, Self>) -> bool {
false // for now, we don't enforce validity
}
fn find_mir_or_eval_fn(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
instance: ty::Instance<'tcx>,
args: &[OpTy<'tcx>],
ret: Option<(PlaceTy<'tcx>, mir::BasicBlock)>,
_unwind: Option<mir::BasicBlock>, // unwinding is not supported in consts
) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>> {
debug!("find_mir_or_eval_fn: {:?}", instance);
// Only check non-glue functions
if let ty::InstanceDef::Item(def_id) = instance.def {
// Execution might have wandered off into other crates, so we cannot do a stability-
// sensitive check here. But we can at least rule out functions that are not const
// at all.
if ecx.tcx.is_const_fn_raw(def_id) {
// If this function is a `const fn` then under certain circumstances we
// can evaluate call via the query system, thus memoizing all future calls.
if ecx.try_eval_const_fn_call(instance, ret, args)? {
return Ok(None);
}
} else {
// Some functions we support even if they are non-const -- but avoid testing
// that for const fn! We certainly do *not* want to actually call the fn
// though, so be sure we return here.
return if ecx.hook_panic_fn(instance, args, ret)? {
Ok(None)
} else {
throw_unsup_format!("calling non-const function `{}`", instance)
};
}
}
// This is a const fn. Call it.
Ok(Some(match ecx.load_mir(instance.def, None) {
Ok(body) => *body,
Err(err) => {
if let err_unsup!(NoMirFor(ref path)) = err.kind {
return Err(ConstEvalError::NeedsRfc(format!(
"calling extern function `{}`",
path
))
.into());
}
return Err(err);
}
}))
}
fn call_extra_fn(
_ecx: &mut InterpCx<'mir, 'tcx, Self>,
fn_val: !,
_args: &[OpTy<'tcx>],
_ret: Option<(PlaceTy<'tcx>, mir::BasicBlock)>,
_unwind: Option<mir::BasicBlock>,
) -> InterpResult<'tcx> {
match fn_val {}
}
fn call_intrinsic(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
span: Span,
instance: ty::Instance<'tcx>,
args: &[OpTy<'tcx>],
ret: Option<(PlaceTy<'tcx>, mir::BasicBlock)>,
_unwind: Option<mir::BasicBlock>,
) -> InterpResult<'tcx> {
if ecx.emulate_intrinsic(span, instance, args, ret)? {
return Ok(());
}
// An intrinsic that we do not support
let intrinsic_name = ecx.tcx.item_name(instance.def_id());
Err(ConstEvalError::NeedsRfc(format!("calling intrinsic `{}`", intrinsic_name)).into())
}
fn assert_panic(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
_span: Span,
msg: &AssertMessage<'tcx>,
_unwind: Option<mir::BasicBlock>,
) -> InterpResult<'tcx> {
use rustc::mir::interpret::PanicInfo::*;
Err(match msg {
BoundsCheck { ref len, ref index } => {
let len = ecx
.read_immediate(ecx.eval_operand(len, None)?)
.expect("can't eval len")
.to_scalar()?
.to_machine_usize(&*ecx)?;
let index = ecx
.read_immediate(ecx.eval_operand(index, None)?)
.expect("can't eval index")
.to_scalar()?
.to_machine_usize(&*ecx)?;
err_panic!(BoundsCheck { len, index })
}
Overflow(op) => err_panic!(Overflow(*op)),
OverflowNeg => err_panic!(OverflowNeg),
DivisionByZero => err_panic!(DivisionByZero),
RemainderByZero => err_panic!(RemainderByZero),
ResumedAfterReturn(generator_kind) => err_panic!(ResumedAfterReturn(*generator_kind)),
ResumedAfterPanic(generator_kind) => err_panic!(ResumedAfterPanic(*generator_kind)),
Panic { .. } => bug!("`Panic` variant cannot occur in MIR"),
}
.into())
}
fn ptr_to_int(_mem: &Memory<'mir, 'tcx, Self>, _ptr: Pointer) -> InterpResult<'tcx, u64> {
Err(ConstEvalError::NeedsRfc("pointer-to-integer cast".to_string()).into())
}
fn binary_ptr_op(
_ecx: &InterpCx<'mir, 'tcx, Self>,
_bin_op: mir::BinOp,
_left: ImmTy<'tcx>,
_right: ImmTy<'tcx>,
) -> InterpResult<'tcx, (Scalar, bool, Ty<'tcx>)> {
Err(ConstEvalError::NeedsRfc("pointer arithmetic or comparison".to_string()).into())
}
fn find_foreign_static(
_tcx: TyCtxt<'tcx>,
_def_id: DefId,
) -> InterpResult<'tcx, Cow<'tcx, Allocation<Self::PointerTag>>> {
throw_unsup!(ReadForeignStatic)
}
#[inline(always)]
fn init_allocation_extra<'b>(
_memory_extra: &MemoryExtra,
_id: AllocId,
alloc: Cow<'b, Allocation>,
_kind: Option<MemoryKind<!>>,
) -> (Cow<'b, Allocation<Self::PointerTag>>, Self::PointerTag) {
// We do not use a tag so we can just cheaply forward the allocation
(alloc, ())
}
#[inline(always)]
fn tag_static_base_pointer(_memory_extra: &MemoryExtra, _id: AllocId) -> Self::PointerTag {
()
}
fn box_alloc(
_ecx: &mut InterpCx<'mir, 'tcx, Self>,
_dest: PlaceTy<'tcx>,
) -> InterpResult<'tcx> {
Err(ConstEvalError::NeedsRfc("heap allocations via `box` keyword".to_string()).into())
}
fn before_terminator(ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
{
let steps = &mut ecx.machine.steps_since_detector_enabled;
*steps += 1;
if *steps < 0 {
return Ok(());
}
*steps %= DETECTOR_SNAPSHOT_PERIOD;
if *steps != 0 {
return Ok(());
}
}
let span = ecx.frame().span;
ecx.machine.loop_detector.observe_and_analyze(*ecx.tcx, span, &ecx.memory, &ecx.stack[..])
}
#[inline(always)]
fn stack_push(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
Ok(())
}
fn before_access_static(
memory_extra: &MemoryExtra,
_allocation: &Allocation,
) -> InterpResult<'tcx> {
if memory_extra.can_access_statics {
Ok(())
} else {
Err(ConstEvalError::ConstAccessesStatic.into())
}
}
}
// Please do not add any code below the above `Machine` trait impl. I (oli-obk) plan more cleanups
// so we can end up having a file with just that impl, but for now, let's keep the impl discoverable
// at the bottom of this file.

23
src/librustc_mir/interpret/terminator.rs
View File

@ -7,8 +7,7 @@ use rustc_target::spec::abi::Abi;
use syntax::source_map::Span;
use super::{
FnVal, GlobalId, ImmTy, InterpCx, InterpResult, MPlaceTy, Machine, OpTy, PlaceTy,
StackPopCleanup,
FnVal, ImmTy, InterpCx, InterpResult, MPlaceTy, Machine, OpTy, PlaceTy, StackPopCleanup,
};
impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
@ -402,26 +401,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
}
}
/// Evaluate a const function where all arguments (if any) are zero-sized types.
/// The evaluation is memoized thanks to the query system.
// FIXME: Consider moving this to `const_eval.rs`.
pub(crate) fn eval_const_fn_call(
&mut self,
gid: GlobalId<'tcx>,
ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
) -> InterpResult<'tcx> {
trace!("eval_const_fn_call: {:?}", gid);
let place = self.const_eval_raw(gid)?;
let dest = ret.ok_or_else(|| err_ub!(Unreachable))?.0;
self.copy_op(place.into(), dest)?;
self.return_to_block(ret.map(|r| r.1))?;
self.dump_place(*dest);
return Ok(());
}
fn drop_in_place(
&mut self,
place: PlaceTy<'tcx, M::PointerTag>,

8
src/test/ui/consts/uninhabited-const-issue-61744.rs
View File

@ -5,15 +5,15 @@ pub const unsafe fn fake_type<T>() -> T {
}
pub const unsafe fn hint_unreachable() -> ! {
fake_type() //~ ERROR cycle detected when const-evaluating `hint_unreachable` [E0391]
fake_type() //~ ERROR evaluation of constant value failed
}
trait Const {
const CONSTANT: i32 = unsafe { fake_type() };
const CONSTANT: i32 = unsafe { fake_type() }; //~ ERROR any use of this value will cause an err
}
impl <T> Const for T {}
impl<T> Const for T {}
pub fn main() -> () {
dbg!(i32::CONSTANT);
dbg!(i32::CONSTANT); //~ ERROR erroneous constant used
}

105
src/test/ui/consts/uninhabited-const-issue-61744.stderr
View File

@ -1,21 +1,96 @@
error[E0391]: cycle detected when const-evaluating `hint_unreachable`
error[E0080]: evaluation of constant value failed
--> $DIR/uninhabited-const-issue-61744.rs:8:5
|
LL | hint_unreachable()
| ------------------
| |
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
| inside call to `hint_unreachable` at $DIR/uninhabited-const-issue-61744.rs:4:5
...
LL | fake_type()
| ^^^^^^^^^^^
|
note: ...which requires const-evaluating `fake_type`...
--> $DIR/uninhabited-const-issue-61744.rs:4:5
|
LL | hint_unreachable()
| ^^^^^^^^^^^^^^^^^^
= note: ...which again requires const-evaluating `hint_unreachable`, completing the cycle
note: cycle used when const-evaluating `fake_type`
--> $DIR/uninhabited-const-issue-61744.rs:4:5
|
LL | hint_unreachable()
| ^^^^^^^^^^^^^^^^^^
| |
| reached the configured maximum number of stack frames
| inside call to `fake_type::<!>` at $DIR/uninhabited-const-issue-61744.rs:8:5
error: aborting due to previous error
error: any use of this value will cause an error
--> $DIR/uninhabited-const-issue-61744.rs:12:36
|
LL | const CONSTANT: i32 = unsafe { fake_type() };
| -------------------------------^^^^^^^^^^^---
| |
| referenced constant has errors
|
= note: `#[deny(const_err)]` on by default
For more information about this error, try `rustc --explain E0391`.
error[E0080]: erroneous constant used
--> $DIR/uninhabited-const-issue-61744.rs:18:10
|
LL | dbg!(i32::CONSTANT);
| ^^^^^^^^^^^^^ referenced constant has errors
error: aborting due to 3 previous errors
For more information about this error, try `rustc --explain E0080`.