src/librustc_mir/const_eval/eval_queries.rs - third_party/rust - Git at Google

 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 rustc_span::source_map::Span;
 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.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.assert_ptr();
             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.assert_ptr();
                 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.assert_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) => {}
             // 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_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::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");

                 // 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 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")
             }
         })
 }
	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 rustc_span::source_map::Span;
	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.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.assert_ptr();
	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.assert_ptr();
	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.assert_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) => {}
	// 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_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::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");

	// 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 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")
	}
	})
	}