diff --git a/src/librustc/mir/interpret/error.rs b/src/librustc/mir/interpret/error.rs index 0b33408edf02..4b1fad5d0b3e 100644 --- a/src/librustc/mir/interpret/error.rs +++ b/src/librustc/mir/interpret/error.rs @@ -565,8 +565,10 @@ impl fmt::Debug for UnsupportedOpInfo<'tcx> { pub enum ResourceExhaustionInfo { /// The stack grew too big. StackFrameLimitReached, - /// The program ran into an infinite loop. - InfiniteLoop, + /// The program ran for too long. + /// + /// The exact limit is set by the `const_eval_limit` attribute. + TimeLimitReached, } impl fmt::Debug for ResourceExhaustionInfo { @@ -576,11 +578,7 @@ impl fmt::Debug for ResourceExhaustionInfo { StackFrameLimitReached => { write!(f, "reached the configured maximum number of stack frames") } - InfiniteLoop => write!( - f, - "duplicate interpreter state observed here, const evaluation will never \ - terminate" - ), + TimeLimitReached => write!(f, "exceeded interpreter time limit"), } } } diff --git a/src/librustc_mir/const_eval/machine.rs b/src/librustc_mir/const_eval/machine.rs index bb661d3d2a30..22b01be299b1 100644 --- a/src/librustc_mir/const_eval/machine.rs +++ b/src/librustc_mir/const_eval/machine.rs @@ -3,7 +3,6 @@ use rustc::ty::layout::HasTyCtxt; use rustc::ty::{self, Ty}; use std::borrow::{Borrow, Cow}; use std::collections::hash_map::Entry; -use std::convert::TryFrom; use std::hash::Hash; use rustc_data_structures::fx::FxHashMap; @@ -13,13 +12,13 @@ use rustc_span::source_map::Span; use rustc_span::symbol::Symbol; use crate::interpret::{ - self, snapshot, AllocId, Allocation, GlobalId, ImmTy, InterpCx, InterpResult, Memory, - MemoryKind, OpTy, PlaceTy, Pointer, Scalar, + self, AllocId, Allocation, GlobalId, ImmTy, InterpCx, InterpResult, Memory, MemoryKind, OpTy, + PlaceTy, Pointer, Scalar, }; use super::error::*; -impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> { +impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter> { /// Evaluate a const function where all arguments (if any) are zero-sized types. /// The evaluation is memoized thanks to the query system. /// @@ -86,22 +85,13 @@ impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> { } } -/// 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, - - pub(super) is_detector_enabled: bool, - - /// Extra state to detect loops. - pub(super) loop_detector: snapshot::InfiniteLoopDetector<'mir, 'tcx>, +/// Extra machine state for CTFE, and the Machine instance +pub struct CompileTimeInterpreter { + /// For now, the number of terminators that can be evaluated before we throw a resource + /// exhuastion error. + /// + /// Setting this to `0` disables the limit and allows the interpreter to run forever. + pub steps_remaining: usize, } #[derive(Copy, Clone, Debug)] @@ -110,16 +100,9 @@ pub struct MemoryExtra { pub(super) can_access_statics: bool, } -impl<'mir, 'tcx> CompileTimeInterpreter<'mir, 'tcx> { +impl CompileTimeInterpreter { pub(super) fn new(const_eval_limit: usize) -> Self { - let steps_until_detector_enabled = - isize::try_from(const_eval_limit).unwrap_or(std::isize::MAX); - - CompileTimeInterpreter { - loop_detector: Default::default(), - steps_since_detector_enabled: -steps_until_detector_enabled, - is_detector_enabled: const_eval_limit != 0, - } + CompileTimeInterpreter { steps_remaining: const_eval_limit } } } @@ -173,8 +156,7 @@ impl interpret::AllocMap for FxHashMap { } } -crate type CompileTimeEvalContext<'mir, 'tcx> = - InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>; +crate type CompileTimeEvalContext<'mir, 'tcx> = InterpCx<'mir, 'tcx, CompileTimeInterpreter>; impl interpret::MayLeak for ! { #[inline(always)] @@ -184,7 +166,7 @@ impl interpret::MayLeak for ! { } } -impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir, 'tcx> { +impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter { type MemoryKinds = !; type PointerTag = (); type ExtraFnVal = !; @@ -346,26 +328,17 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir, } fn before_terminator(ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> { - if !ecx.machine.is_detector_enabled { + // The step limit has already been hit in a previous call to `before_terminator`. + if ecx.machine.steps_remaining == 0 { return Ok(()); } - { - 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(()); - } + ecx.machine.steps_remaining -= 1; + if ecx.machine.steps_remaining == 0 { + throw_exhaust!(TimeLimitReached) } - let span = ecx.frame().span; - ecx.machine.loop_detector.observe_and_analyze(*ecx.tcx, span, &ecx.memory, &ecx.stack[..]) + Ok(()) } #[inline(always)] diff --git a/src/librustc_mir/interpret/memory.rs b/src/librustc_mir/interpret/memory.rs index 82a467c7ba92..03be71f6174a 100644 --- a/src/librustc_mir/interpret/memory.rs +++ b/src/librustc_mir/interpret/memory.rs @@ -112,25 +112,6 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> HasDataLayout for Memory<'mir, 'tcx, M> } } -// FIXME: Really we shouldn't clone memory, ever. Snapshot machinery should instead -// carefully copy only the reachable parts. -impl<'mir, 'tcx, M> Clone for Memory<'mir, 'tcx, M> -where - M: Machine<'mir, 'tcx, PointerTag = (), AllocExtra = ()>, - M::MemoryExtra: Copy, - M::MemoryMap: AllocMap, Allocation)>, -{ - fn clone(&self) -> Self { - Memory { - alloc_map: self.alloc_map.clone(), - extra_fn_ptr_map: self.extra_fn_ptr_map.clone(), - dead_alloc_map: self.dead_alloc_map.clone(), - extra: self.extra, - tcx: self.tcx, - } - } -} - impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> { pub fn new(tcx: TyCtxtAt<'tcx>, extra: M::MemoryExtra) -> Self { Memory {