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Diffstat (limited to 'compiler/rustc_const_eval/src/const_eval/eval_queries.rs')
| -rw-r--r-- | compiler/rustc_const_eval/src/const_eval/eval_queries.rs | 395 |
1 files changed, 395 insertions, 0 deletions
diff --git a/compiler/rustc_const_eval/src/const_eval/eval_queries.rs b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs new file mode 100644 index 000000000..975fb4b22 --- /dev/null +++ b/compiler/rustc_const_eval/src/const_eval/eval_queries.rs @@ -0,0 +1,395 @@ +use super::{CompileTimeEvalContext, CompileTimeInterpreter, ConstEvalErr}; +use crate::interpret::eval_nullary_intrinsic; +use crate::interpret::{ + intern_const_alloc_recursive, Allocation, ConstAlloc, ConstValue, CtfeValidationMode, GlobalId, + Immediate, InternKind, InterpCx, InterpResult, MPlaceTy, MemoryKind, OpTy, RefTracking, + ScalarMaybeUninit, StackPopCleanup, InterpError, +}; + +use rustc_hir::def::DefKind; +use rustc_middle::mir; +use rustc_middle::mir::interpret::ErrorHandled; +use rustc_middle::mir::pretty::display_allocation; +use rustc_middle::traits::Reveal; +use rustc_middle::ty::layout::LayoutOf; +use rustc_middle::ty::print::with_no_trimmed_paths; +use rustc_middle::ty::{self, subst::Subst, TyCtxt}; +use rustc_span::source_map::Span; +use rustc_target::abi::{self, Abi}; +use std::borrow::Cow; +use std::convert::TryInto; + +const NOTE_ON_UNDEFINED_BEHAVIOR_ERROR: &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; + assert!( + cid.promoted.is_some() + || matches!( + ecx.tcx.def_kind(cid.instance.def_id()), + DefKind::Const + | DefKind::Static(_) + | DefKind::ConstParam + | DefKind::AnonConst + | DefKind::InlineConst + | DefKind::AssocConst + ), + "Unexpected DefKind: {:?}", + ecx.tcx.def_kind(cid.instance.def_id()) + ); + let layout = ecx.layout_of(body.bound_return_ty().subst(tcx, cid.instance.substs))?; + assert!(!layout.is_unsized()); + let ret = ecx.allocate(layout, MemoryKind::Stack)?; + + trace!( + "eval_body_using_ecx: pushing stack frame for global: {}{}", + with_no_trimmed_paths!(ty::tls::with(|tcx| tcx.def_path_str(cid.instance.def_id()))), + cid.promoted.map_or_else(String::new, |p| format!("::promoted[{:?}]", p)) + ); + + ecx.push_stack_frame( + cid.instance, + body, + &ret.into(), + StackPopCleanup::Root { cleanup: false }, + )?; + + // The main interpreter loop. + ecx.run()?; + + // Intern the result + let intern_kind = if cid.promoted.is_some() { + InternKind::Promoted + } else { + match tcx.static_mutability(cid.instance.def_id()) { + Some(m) => InternKind::Static(m), + None => InternKind::Constant, + } + }; + intern_const_alloc_recursive(ecx, intern_kind, &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>, + 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.const_eval_limit(), can_access_statics), + ) +} + +/// This function converts an interpreter value into a constant that is meant for use in the +/// type system. +#[instrument(skip(ecx), level = "debug")] +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(abi::Scalar::Initialized { .. }) => 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_mir_constant, 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() + }; + + debug!(?immediate); + + // We know `offset` is relative to the allocation, so we can use `into_parts`. + let to_const_value = |mplace: &MPlaceTy<'_>| { + debug!("to_const_value(mplace: {:?})", mplace); + match mplace.ptr.into_parts() { + (Some(alloc_id), offset) => { + let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory(); + ConstValue::ByRef { alloc, offset } + } + (None, offset) => { + assert!(mplace.layout.is_zst()); + assert_eq!( + offset.bytes() % mplace.layout.align.abi.bytes(), + 0, + "this MPlaceTy must come from a validated constant, thus we can assume the \ + alignment is correct", + ); + ConstValue::ZeroSized + } + } + }; + match immediate { + Ok(ref mplace) => to_const_value(mplace), + // see comment on `let try_as_immediate` above + Err(imm) => match *imm { + _ if imm.layout.is_zst() => ConstValue::ZeroSized, + Immediate::Scalar(x) => match x { + ScalarMaybeUninit::Scalar(s) => ConstValue::Scalar(s), + ScalarMaybeUninit::Uninit => to_const_value(&op.assert_mem_place()), + }, + Immediate::ScalarPair(a, b) => { + debug!("ScalarPair(a: {:?}, b: {:?})", a, b); + // We know `offset` is relative to the allocation, so we can use `into_parts`. + let (data, start) = match a.to_pointer(ecx).unwrap().into_parts() { + (Some(alloc_id), offset) => { + (ecx.tcx.global_alloc(alloc_id).unwrap_memory(), offset.bytes()) + } + (None, _offset) => ( + ecx.tcx.intern_const_alloc(Allocation::from_bytes_byte_aligned_immutable( + 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 } + } + Immediate::Uninit => to_const_value(&op.assert_mem_place()), + }, + } +} + +#[instrument(skip(tcx), level = "debug")] +pub(crate) fn turn_into_const_value<'tcx>( + tcx: TyCtxt<'tcx>, + constant: ConstAlloc<'tcx>, + key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>, +) -> ConstValue<'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 mplace = ecx.raw_const_to_mplace(constant).expect( + "can only fail if layout computation failed, \ + which should have given a good error before ever invoking this function", + ); + assert!( + !is_static || cid.promoted.is_some(), + "the `eval_to_const_value_raw` query should not be used for statics, use `eval_to_allocation` instead" + ); + + // Turn this into a proper constant. + let const_val = op_to_const(&ecx, &mplace.into()); + debug!(?const_val); + + const_val +} + +#[instrument(skip(tcx), level = "debug")] +pub fn eval_to_const_value_raw_provider<'tcx>( + tcx: TyCtxt<'tcx>, + key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>, +) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> { + assert!(key.param_env.is_const()); + // see comment in eval_to_allocation_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.eval_to_const_value_raw(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(tcx, key.param_env); + let ty::FnDef(_, substs) = ty.kind() else { + 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.into_kind(), stacktrace: vec![], span }; + error.report_as_error(tcx.at(span), "could not evaluate nullary intrinsic") + }); + } + + tcx.eval_to_allocation_raw(key).map(|val| turn_into_const_value(tcx, val, key)) +} + +#[instrument(skip(tcx), level = "debug")] +pub fn eval_to_allocation_raw_provider<'tcx>( + tcx: TyCtxt<'tcx>, + key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>, +) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'tcx> { + assert!(key.param_env.is_const()); + // 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.eval_to_allocation_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 = with_no_trimmed_paths!(key.value.instance.to_string()); + trace!("const eval: {:?} ({})", key, instance); + } + + let cid = key.value; + let def = cid.instance.def.with_opt_param(); + let is_static = tcx.is_static(def.did); + + let mut ecx = InterpCx::new( + tcx, + tcx.def_span(def.did), + key.param_env, + // Statics (and promoteds inside statics) may access other statics, because unlike consts + // they do not have to behave "as if" they were evaluated at runtime. + CompileTimeInterpreter::new(tcx.const_eval_limit(), /*can_access_statics:*/ is_static), + ); + + let res = ecx.load_mir(cid.instance.def, cid.promoted); + match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) { + Err(error) => { + let err = ConstEvalErr::new(&ecx, error, None); + // Some CTFE errors raise just a lint, not a hard error; see + // <https://github.com/rust-lang/rust/issues/71800>. + let is_hard_err = if let Some(def) = def.as_local() { + // (Associated) consts only emit a lint, since they might be unused. + !matches!(tcx.def_kind(def.did.to_def_id()), DefKind::Const | DefKind::AssocConst) + // check if the inner InterpError is hard + || err.error.is_hard_err() + } else { + // use of broken constant from other crate: always an error + true + }; + + if is_hard_err { + let msg = if is_static { + Cow::from("could not evaluate static initializer") + } else { + // If the current item has generics, we'd like to enrich the message with the + // instance and its substs: to show the actual compile-time values, in addition to + // the expression, leading to the const eval error. + let instance = &key.value.instance; + if !instance.substs.is_empty() { + let instance = with_no_trimmed_paths!(instance.to_string()); + let msg = format!("evaluation of `{}` failed", instance); + Cow::from(msg) + } else { + Cow::from("evaluation of constant value failed") + } + }; + + Err(err.report_as_error(ecx.tcx.at(err.span), &msg)) + } else { + let hir_id = tcx.hir().local_def_id_to_hir_id(def.as_local().unwrap().did); + Err(err.report_as_lint( + tcx.at(tcx.def_span(def.did)), + "any use of this value will cause an error", + hir_id, + Some(err.span), + )) + } + } + Ok(mplace) => { + // Since evaluation had no errors, validate the resulting constant. + // This is a separate `try` block to provide more targeted error reporting. + let validation = try { + let mut ref_tracking = RefTracking::new(mplace); + let mut inner = false; + while let Some((mplace, path)) = ref_tracking.todo.pop() { + let mode = match tcx.static_mutability(cid.instance.def_id()) { + Some(_) if cid.promoted.is_some() => { + // Promoteds in statics are allowed to point to statics. + CtfeValidationMode::Const { inner, allow_static_ptrs: true } + } + Some(_) => CtfeValidationMode::Regular, // a `static` + None => CtfeValidationMode::Const { inner, allow_static_ptrs: false }, + }; + ecx.const_validate_operand(&mplace.into(), path, &mut ref_tracking, mode)?; + inner = true; + } + }; + let alloc_id = mplace.ptr.provenance.unwrap(); + if let Err(error) = validation { + // Validation failed, report an error. This is always a hard error. + let err = ConstEvalErr::new(&ecx, error, None); + Err(err.struct_error( + ecx.tcx, + "it is undefined behavior to use this value", + |diag| { + if matches!(err.error, InterpError::UndefinedBehavior(_)) { + diag.note(NOTE_ON_UNDEFINED_BEHAVIOR_ERROR); + } + diag.note(&format!( + "the raw bytes of the constant ({}", + display_allocation( + *ecx.tcx, + ecx.tcx.global_alloc(alloc_id).unwrap_memory().inner() + ) + )); + }, + )) + } else { + // Convert to raw constant + Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty }) + } + } + } +} |