| 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, Immediate, InternKind, |
| InterpCx, InterpResult, MPlaceTy, MemoryKind, OpTy, RawConst, RefTracking, Scalar, |
| ScalarMaybeUninit, StackPopCleanup, |
| }; |
| use rustc_hir::def::DefKind; |
| use rustc_middle::mir; |
| use rustc_middle::mir::interpret::{ConstEvalErr, ErrorHandled}; |
| use rustc_middle::traits::Reveal; |
| use rustc_middle::ty::{self, subst::Subst, TyCtxt}; |
| use rustc_span::source_map::Span; |
| use rustc_target::abi::{Abi, LayoutOf}; |
| use std::convert::TryInto; |
| |
| 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; |
| 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, |
| Some(ret.into()), |
| StackPopCleanup::None { cleanup: false }, |
| )?; |
| |
| // The main interpreter loop. |
| ecx.run()?; |
| |
| // Intern the result |
| let intern_kind = match tcx.static_mutability(cid.instance.def_id()) { |
| Some(m) => InternKind::Static(m), |
| None if cid.promoted.is_some() => InternKind::Promoted, |
| _ => InternKind::Constant, |
| }; |
| intern_const_alloc_recursive( |
| ecx, |
| intern_kind, |
| ret, |
| body.ignore_interior_mut_in_const_validation, |
| ); |
| |
| 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>, |
| root_span: Span, |
| param_env: ty::ParamEnv<'tcx>, |
| can_access_statics: bool, |
| ) -> CompileTimeEvalContext<'mir, 'tcx> { |
| debug!("mk_eval_cx: {:?}", param_env); |
| InterpCx::new( |
| tcx, |
| root_span, |
| param_env, |
| CompileTimeInterpreter::new(tcx.sess.const_eval_limit()), |
| MemoryExtra { can_access_statics }, |
| ) |
| } |
| |
| pub(super) fn op_to_const<'tcx>( |
| ecx: &CompileTimeEvalContext<'_, 'tcx>, |
| op: OpTy<'tcx>, |
| ) -> ConstValue<'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 uninitialized 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 `ScalarMaybeUninit`, 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 { |
| Abi::Scalar(..) => true, |
| 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 destructure_const, 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(ecx) |
| }; |
| |
| let to_const_value = |mplace: MPlaceTy<'_>| match mplace.ptr { |
| Scalar::Ptr(ptr) => { |
| let alloc = ecx.tcx.global_alloc(ptr.alloc_id).unwrap_memory(); |
| ConstValue::ByRef { alloc, offset: ptr.offset } |
| } |
| Scalar::Raw { data, .. } => { |
| assert!(mplace.layout.is_zst()); |
| assert_eq!( |
| data, |
| mplace.layout.align.abi.bytes().into(), |
| "this MPlaceTy must come from `try_as_mplace` being used on a zst, so we know what |
| value this integer address must have", |
| ); |
| ConstValue::Scalar(Scalar::zst()) |
| } |
| }; |
| match immediate { |
| Ok(mplace) => to_const_value(mplace), |
| // see comment on `let try_as_immediate` above |
| Err(imm) => match *imm { |
| Immediate::Scalar(x) => match x { |
| ScalarMaybeUninit::Scalar(s) => ConstValue::Scalar(s), |
| ScalarMaybeUninit::Uninit => to_const_value(op.assert_mem_place(ecx)), |
| }, |
| Immediate::ScalarPair(a, b) => { |
| let (data, start) = match a.not_undef().unwrap() { |
| Scalar::Ptr(ptr) => { |
| (ecx.tcx.global_alloc(ptr.alloc_id).unwrap_memory(), 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).unwrap(); |
| let start = start.try_into().unwrap(); |
| let len: usize = len.try_into().unwrap(); |
| ConstValue::Slice { data, start, end: start + len } |
| } |
| }, |
| } |
| } |
| |
| fn validate_and_turn_into_const<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| constant: RawConst<'tcx>, |
| key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>, |
| ) -> ::rustc_middle::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)?; |
| |
| // FIXME do not validate promoteds until a decision on |
| // https://github.com/rust-lang/rust/issues/67465 is made |
| if cid.promoted.is_none() { |
| let mut ref_tracking = RefTracking::new(mplace); |
| while let Some((mplace, path)) = ref_tracking.todo.pop() { |
| ecx.const_validate_operand( |
| mplace.into(), |
| path, |
| &mut ref_tracking, |
| /*may_ref_to_static*/ ecx.memory.extra.can_access_statics, |
| )?; |
| } |
| } |
| // 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.assert_ptr(); |
| Ok(ConstValue::ByRef { |
| alloc: ecx.tcx.global_alloc(ptr.alloc_id).unwrap_memory(), |
| offset: ptr.offset, |
| }) |
| } else { |
| Ok(op_to_const(&ecx, mplace.into())) |
| } |
| })(); |
| |
| val.map_err(|error| { |
| let err = error_to_const_error(&ecx, error, None); |
| err.struct_error(ecx.tcx, "it is undefined behavior to use this value", |mut diag| { |
| diag.note(note_on_undefined_behavior_error()); |
| diag.emit(); |
| }) |
| }) |
| } |
| |
| pub fn const_eval_validated_provider<'tcx>( |
| tcx: TyCtxt<'tcx>, |
| key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>, |
| ) -> ::rustc_middle::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; |
| key.param_env = key.param_env.with_user_facing(); |
| match tcx.const_eval_validated(key) { |
| // try again with reveal all as requested |
| Err(ErrorHandled::TooGeneric) => {} |
| // deduplicate 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_env(tcx, key.param_env); |
| 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_middle::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; |
| key.param_env = key.param_env.with_user_facing(); |
| match tcx.const_eval_raw(key) { |
| // try again with reveal all as requested |
| Err(ErrorHandled::TooGeneric) => {} |
| // deduplicate 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 let Some(def_id) = def_id.as_local() { |
| if tcx.has_typeck_tables(def_id) { |
| if let Some(error_reported) = tcx.typeck_tables_of(def_id).tainted_by_errors { |
| return Err(ErrorHandled::Reported(error_reported)); |
| } |
| } |
| } |
| |
| let is_static = tcx.is_static(def_id); |
| |
| let mut ecx = InterpCx::new( |
| tcx, |
| tcx.def_span(cid.instance.def_id()), |
| key.param_env, |
| CompileTimeInterpreter::new(tcx.sess.const_eval_limit()), |
| 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)) |
| .map(|place| RawConst { alloc_id: place.ptr.assert_ptr().alloc_id, ty: place.layout.ty }) |
| .map_err(|error| { |
| let err = error_to_const_error(&ecx, error, None); |
| // 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.at(ecx.cur_span()), |
| "could not evaluate static initializer", |
| ); |
| |
| // If this is `Reveal:All`, then we need to make sure an error is reported but if |
| // this is `Reveal::UserFacing`, then it's expected that we could get a |
| // `TooGeneric` error. When we fall back to `Reveal::All`, then it will either |
| // succeed or we'll report this error then. |
| if key.param_env.reveal() == Reveal::All { |
| tcx.sess.delay_span_bug( |
| err.span, |
| &format!("static eval failure did not emit an error: {:#?}", v), |
| ); |
| } |
| |
| v |
| } else if let Some(def_id) = def_id.as_local() { |
| // constant defined in this crate, we can figure out a lint level! |
| match tcx.def_kind(def_id.to_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 |
| DefKind::Const | DefKind::AssocConst => { |
| let hir_id = tcx.hir().as_local_hir_id(def_id); |
| 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), |
| Some(err.span), |
| ) |
| } |
| // anything else (array lengths, enum initializers, constant patterns) are |
| // reported as hard errors |
| } else { |
| err.report_as_error( |
| ecx.tcx.at(ecx.cur_span()), |
| "evaluation of constant value failed", |
| ) |
| } |
| } |
| } |
| } else { |
| // use of broken constant from other crate |
| err.report_as_error(ecx.tcx.at(ecx.cur_span()), "could not evaluate constant") |
| } |
| }) |
| } |
