381 lines
16 KiB
Rust
381 lines
16 KiB
Rust
use super::{error_to_const_error, CompileTimeEvalContext, CompileTimeInterpreter, MemoryExtra};
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use crate::interpret::eval_nullary_intrinsic;
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use crate::interpret::{
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intern_const_alloc_recursive, Allocation, ConstValue, GlobalId, ImmTy, Immediate, InternKind,
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InterpCx, InterpResult, MPlaceTy, MemoryKind, OpTy, RawConst, RefTracking, Scalar,
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ScalarMaybeUndef, StackPopCleanup,
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};
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use rustc::mir;
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use rustc::mir::interpret::{ConstEvalErr, ErrorHandled};
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use rustc::traits::Reveal;
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use rustc::ty::{self, layout, layout::LayoutOf, subst::Subst, TyCtxt};
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use rustc_hir::def::DefKind;
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use rustc_span::source_map::Span;
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use std::convert::TryInto;
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pub fn note_on_undefined_behavior_error() -> &'static str {
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"The rules on what exactly is undefined behavior aren't clear, \
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so this check might be overzealous. Please open an issue on the rustc \
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repository if you believe it should not be considered undefined behavior."
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}
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// Returns a pointer to where the result lives
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fn eval_body_using_ecx<'mir, 'tcx>(
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ecx: &mut CompileTimeEvalContext<'mir, 'tcx>,
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cid: GlobalId<'tcx>,
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body: &'mir mir::Body<'tcx>,
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) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
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debug!("eval_body_using_ecx: {:?}, {:?}", cid, ecx.param_env);
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let tcx = ecx.tcx.tcx;
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let layout = ecx.layout_of(body.return_ty().subst(tcx, cid.instance.substs))?;
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assert!(!layout.is_unsized());
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let ret = ecx.allocate(layout, MemoryKind::Stack);
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let name = ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id()));
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let prom = cid.promoted.map_or(String::new(), |p| format!("::promoted[{:?}]", p));
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trace!("eval_body_using_ecx: pushing stack frame for global: {}{}", name, prom);
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// Assert all args (if any) are zero-sized types; `eval_body_using_ecx` doesn't
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// make sense if the body is expecting nontrivial arguments.
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// (The alternative would be to use `eval_fn_call` with an args slice.)
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for arg in body.args_iter() {
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let decl = body.local_decls.get(arg).expect("arg missing from local_decls");
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let layout = ecx.layout_of(decl.ty.subst(tcx, cid.instance.substs))?;
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assert!(layout.is_zst())
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}
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ecx.push_stack_frame(
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cid.instance,
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body.span,
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body,
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Some(ret.into()),
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StackPopCleanup::None { cleanup: false },
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)?;
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// The main interpreter loop.
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ecx.run()?;
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// Intern the result
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let intern_kind = match tcx.static_mutability(cid.instance.def_id()) {
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Some(m) => InternKind::Static(m),
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None if cid.promoted.is_some() => InternKind::Promoted,
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_ => InternKind::Constant,
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};
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intern_const_alloc_recursive(
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ecx,
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intern_kind,
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ret,
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body.ignore_interior_mut_in_const_validation,
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)?;
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debug!("eval_body_using_ecx done: {:?}", *ret);
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Ok(ret)
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}
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/// The `InterpCx` is only meant to be used to do field and index projections into constants for
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/// `simd_shuffle` and const patterns in match arms.
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///
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/// The function containing the `match` that is currently being analyzed may have generic bounds
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/// that inform us about the generic bounds of the constant. E.g., using an associated constant
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/// of a function's generic parameter will require knowledge about the bounds on the generic
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/// parameter. These bounds are passed to `mk_eval_cx` via the `ParamEnv` argument.
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pub(super) fn mk_eval_cx<'mir, 'tcx>(
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tcx: TyCtxt<'tcx>,
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span: Span,
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param_env: ty::ParamEnv<'tcx>,
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can_access_statics: bool,
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) -> CompileTimeEvalContext<'mir, 'tcx> {
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debug!("mk_eval_cx: {:?}", param_env);
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InterpCx::new(
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tcx.at(span),
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param_env,
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CompileTimeInterpreter::new(),
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MemoryExtra { can_access_statics },
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)
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}
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pub(super) fn op_to_const<'tcx>(
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ecx: &CompileTimeEvalContext<'_, 'tcx>,
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op: OpTy<'tcx>,
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) -> &'tcx ty::Const<'tcx> {
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// We do not have value optimizations for everything.
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// Only scalars and slices, since they are very common.
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// Note that further down we turn scalars of undefined bits back to `ByRef`. These can result
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// from scalar unions that are initialized with one of their zero sized variants. We could
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// instead allow `ConstValue::Scalar` to store `ScalarMaybeUndef`, but that would affect all
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// the usual cases of extracting e.g. a `usize`, without there being a real use case for the
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// `Undef` situation.
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let try_as_immediate = match op.layout.abi {
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layout::Abi::Scalar(..) => true,
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layout::Abi::ScalarPair(..) => match op.layout.ty.kind {
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ty::Ref(_, inner, _) => match inner.kind {
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ty::Slice(elem) => elem == ecx.tcx.types.u8,
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ty::Str => true,
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_ => false,
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},
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_ => false,
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},
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_ => false,
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};
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let immediate = if try_as_immediate {
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Err(ecx.read_immediate(op).expect("normalization works on validated constants"))
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} else {
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// It is guaranteed that any non-slice scalar pair is actually ByRef here.
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// When we come back from raw const eval, we are always by-ref. The only way our op here is
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// by-val is if we are in const_field, i.e., if this is (a field of) something that we
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// "tried to make immediate" before. We wouldn't do that for non-slice scalar pairs or
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// structs containing such.
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op.try_as_mplace(ecx)
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};
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let to_const_value = |mplace: MPlaceTy<'_>| match mplace.ptr {
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Scalar::Ptr(ptr) => {
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let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
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ConstValue::ByRef { alloc, offset: ptr.offset }
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}
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Scalar::Raw { data, .. } => {
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assert!(mplace.layout.is_zst());
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assert_eq!(
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data,
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mplace.layout.align.abi.bytes().into(),
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"this MPlaceTy must come from `try_as_mplace` being used on a zst, so we know what
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value this integer address must have",
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);
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ConstValue::Scalar(Scalar::zst())
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}
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};
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let val = match immediate {
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Ok(mplace) => to_const_value(mplace),
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// see comment on `let try_as_immediate` above
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Err(ImmTy { imm: Immediate::Scalar(x), .. }) => match x {
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ScalarMaybeUndef::Scalar(s) => ConstValue::Scalar(s),
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ScalarMaybeUndef::Undef => to_const_value(op.assert_mem_place(ecx)),
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},
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Err(ImmTy { imm: Immediate::ScalarPair(a, b), .. }) => {
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let (data, start) = match a.not_undef().unwrap() {
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Scalar::Ptr(ptr) => {
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(ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id), ptr.offset.bytes())
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}
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Scalar::Raw { .. } => (
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ecx.tcx.intern_const_alloc(Allocation::from_byte_aligned_bytes(b"" as &[u8])),
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0,
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),
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};
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let len = b.to_machine_usize(&ecx.tcx.tcx).unwrap();
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let start = start.try_into().unwrap();
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let len: usize = len.try_into().unwrap();
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ConstValue::Slice { data, start, end: start + len }
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}
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};
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ecx.tcx.mk_const(ty::Const { val: ty::ConstKind::Value(val), ty: op.layout.ty })
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}
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fn validate_and_turn_into_const<'tcx>(
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tcx: TyCtxt<'tcx>,
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constant: RawConst<'tcx>,
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key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
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) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
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let cid = key.value;
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let def_id = cid.instance.def.def_id();
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let is_static = tcx.is_static(def_id);
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let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env, is_static);
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let val = (|| {
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let mplace = ecx.raw_const_to_mplace(constant)?;
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// FIXME do not validate promoteds until a decision on
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// https://github.com/rust-lang/rust/issues/67465 is made
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if cid.promoted.is_none() {
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let mut ref_tracking = RefTracking::new(mplace);
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while let Some((mplace, path)) = ref_tracking.todo.pop() {
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ecx.validate_operand(mplace.into(), path, Some(&mut ref_tracking))?;
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}
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}
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// Now that we validated, turn this into a proper constant.
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// Statics/promoteds are always `ByRef`, for the rest `op_to_const` decides
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// whether they become immediates.
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if is_static || cid.promoted.is_some() {
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let ptr = mplace.ptr.assert_ptr();
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Ok(tcx.mk_const(ty::Const {
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val: ty::ConstKind::Value(ConstValue::ByRef {
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alloc: ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id),
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offset: ptr.offset,
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}),
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ty: mplace.layout.ty,
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}))
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} else {
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Ok(op_to_const(&ecx, mplace.into()))
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}
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})();
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val.map_err(|error| {
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let err = error_to_const_error(&ecx, error);
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match err.struct_error(ecx.tcx, "it is undefined behavior to use this value", |mut diag| {
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diag.note(note_on_undefined_behavior_error());
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diag.emit();
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}) {
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Ok(_) => ErrorHandled::Reported,
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Err(err) => err,
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}
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})
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}
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pub fn const_eval_validated_provider<'tcx>(
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tcx: TyCtxt<'tcx>,
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key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
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) -> ::rustc::mir::interpret::ConstEvalResult<'tcx> {
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// see comment in const_eval_raw_provider for what we're doing here
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if key.param_env.reveal == Reveal::All {
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let mut key = key;
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key.param_env.reveal = Reveal::UserFacing;
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match tcx.const_eval_validated(key) {
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// try again with reveal all as requested
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Err(ErrorHandled::TooGeneric) => {}
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// dedupliate calls
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other => return other,
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}
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}
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// We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
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// Catch such calls and evaluate them instead of trying to load a constant's MIR.
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if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
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let ty = key.value.instance.ty_env(tcx, key.param_env);
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let substs = match ty.kind {
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ty::FnDef(_, substs) => substs,
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_ => bug!("intrinsic with type {:?}", ty),
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};
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return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
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let span = tcx.def_span(def_id);
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let error = ConstEvalErr { error: error.kind, stacktrace: vec![], span };
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error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic")
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});
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}
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tcx.const_eval_raw(key).and_then(|val| validate_and_turn_into_const(tcx, val, key))
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}
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pub fn const_eval_raw_provider<'tcx>(
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tcx: TyCtxt<'tcx>,
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key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
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) -> ::rustc::mir::interpret::ConstEvalRawResult<'tcx> {
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// Because the constant is computed twice (once per value of `Reveal`), we are at risk of
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// reporting the same error twice here. To resolve this, we check whether we can evaluate the
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// constant in the more restrictive `Reveal::UserFacing`, which most likely already was
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// computed. For a large percentage of constants that will already have succeeded. Only
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// associated constants of generic functions will fail due to not enough monomorphization
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// information being available.
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// In case we fail in the `UserFacing` variant, we just do the real computation.
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if key.param_env.reveal == Reveal::All {
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let mut key = key;
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key.param_env.reveal = Reveal::UserFacing;
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match tcx.const_eval_raw(key) {
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// try again with reveal all as requested
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Err(ErrorHandled::TooGeneric) => {}
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// dedupliate calls
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other => return other,
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}
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}
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if cfg!(debug_assertions) {
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// Make sure we format the instance even if we do not print it.
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// This serves as a regression test against an ICE on printing.
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// The next two lines concatenated contain some discussion:
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// https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
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// subject/anon_const_instance_printing/near/135980032
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let instance = key.value.instance.to_string();
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trace!("const eval: {:?} ({})", key, instance);
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}
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let cid = key.value;
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let def_id = cid.instance.def.def_id();
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if def_id.is_local() && tcx.typeck_tables_of(def_id).tainted_by_errors {
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return Err(ErrorHandled::Reported);
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}
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let is_static = tcx.is_static(def_id);
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let span = tcx.def_span(cid.instance.def_id());
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let mut ecx = InterpCx::new(
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tcx.at(span),
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key.param_env,
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CompileTimeInterpreter::new(),
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MemoryExtra { can_access_statics: is_static },
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);
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let res = ecx.load_mir(cid.instance.def, cid.promoted);
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res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, *body))
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.and_then(|place| {
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Ok(RawConst { alloc_id: place.ptr.assert_ptr().alloc_id, ty: place.layout.ty })
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})
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.map_err(|error| {
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let err = error_to_const_error(&ecx, error);
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// errors in statics are always emitted as fatal errors
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if is_static {
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// Ensure that if the above error was either `TooGeneric` or `Reported`
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// an error must be reported.
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let v = err.report_as_error(ecx.tcx, "could not evaluate static initializer");
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// If this is `Reveal:All`, then we need to make sure an error is reported but if
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// this is `Reveal::UserFacing`, then it's expected that we could get a
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// `TooGeneric` error. When we fall back to `Reveal::All`, then it will either
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// succeed or we'll report this error then.
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if key.param_env.reveal == Reveal::All {
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tcx.sess.delay_span_bug(
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err.span,
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&format!("static eval failure did not emit an error: {:#?}", v),
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);
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}
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v
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} else if def_id.is_local() {
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// constant defined in this crate, we can figure out a lint level!
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match tcx.def_kind(def_id) {
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// constants never produce a hard error at the definition site. Anything else is
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// a backwards compatibility hazard (and will break old versions of winapi for
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// sure)
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//
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// note that validation may still cause a hard error on this very same constant,
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// because any code that existed before validation could not have failed
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// validation thus preventing such a hard error from being a backwards
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// compatibility hazard
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Some(DefKind::Const) | Some(DefKind::AssocConst) => {
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let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
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err.report_as_lint(
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tcx.at(tcx.def_span(def_id)),
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"any use of this value will cause an error",
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hir_id,
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Some(err.span),
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)
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}
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// promoting runtime code is only allowed to error if it references broken
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// constants any other kind of error will be reported to the user as a
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// deny-by-default lint
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_ => {
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if let Some(p) = cid.promoted {
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let span = tcx.promoted_mir(def_id)[p].span;
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if let err_inval!(ReferencedConstant) = err.error {
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err.report_as_error(
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tcx.at(span),
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"evaluation of constant expression failed",
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)
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} else {
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err.report_as_lint(
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tcx.at(span),
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"reaching this expression at runtime will panic or abort",
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tcx.hir().as_local_hir_id(def_id).unwrap(),
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Some(err.span),
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)
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}
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// anything else (array lengths, enum initializers, constant patterns) are
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// reported as hard errors
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} else {
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err.report_as_error(ecx.tcx, "evaluation of constant value failed")
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}
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}
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}
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} else {
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// use of broken constant from other crate
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err.report_as_error(ecx.tcx, "could not evaluate constant")
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}
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})
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}
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