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

 use super::{CompileTimeEvalContext, CompileTimeInterpreter, ConstEvalErr, MemoryExtra};
 use crate::interpret::eval_nullary_intrinsic;
 use crate::interpret::{
     intern_const_alloc_recursive, Allocation, ConstAlloc, ConstValue, GlobalId, Immediate,
     InternKind, InterpCx, InterpResult, MPlaceTy, MemoryKind, OpTy, RefTracking, Scalar,
     ScalarMaybeUninit, StackPopCleanup,
 };

 use rustc_hir::def::DefKind;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::traits::Reveal;
 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::{Abi, LayoutOf};
 use std::convert::{TryFrom, 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 =
         with_no_trimmed_paths(|| 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
     // FIXME: since the DefId of a promoted is the DefId of its owner, this
     // means that promoteds in statics are actually interned like statics!
     // However, this is also currently crucial because we promote mutable
     // non-empty slices in statics to extend their lifetime, and this
     // ensures that they are put into a mutable allocation.
     // For other kinds of promoteds in statics (like array initializers), this is rather silly.
     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 },
     )
 }

 /// This function converts an interpreter value into a constant that is meant for use in the
 /// type system.
 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!(
                 u64::try_from(data).unwrap() % mplace.layout.align.abi.bytes(),
                 0,
                 "this MPlaceTy must come from a validated constant, thus we can assume the \
                 alignment is correct",
             );
             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.check_init().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 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.
     op_to_const(&ecx, mplace.into())
 }

 pub fn eval_to_const_value_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'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.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 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.eval_to_allocation_raw(key).map(|val| turn_into_const_value(tcx, val, key))
 }

 pub fn eval_to_allocation_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'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.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();

     if let Some(def) = def.as_local() {
         if tcx.has_typeck_results(def.did) {
             if let Some(error_reported) = tcx.typeck_opt_const_arg(def).tainted_by_errors {
                 return Err(ErrorHandled::Reported(error_reported));
             }
         }
     }

     let is_static = tcx.is_static(def.did);

     let mut ecx = InterpCx::new(
         tcx,
         tcx.def_span(def.did),
         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);
     match res.and_then(|body| eval_body_using_ecx(&mut ecx, cid, &body)) {
         Err(error) => {
             let err = ConstEvalErr::new(&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),
                     );
                 }

                 Err(v)
             } else if let Some(def) = def.as_local() {
                 // constant defined in this crate, we can figure out a lint level!
                 match tcx.def_kind(def.did.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().local_def_id_to_hir_id(def.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),
                         ))
                     }
                     // 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_opt_const_arg(def.to_global())[p].span;
                             if let err_inval!(ReferencedConstant) = err.error {
                                 Err(err.report_as_error(
                                     tcx.at(span),
                                     "evaluation of constant expression failed",
                                 ))
                             } else {
                                 Err(err.report_as_lint(
                                     tcx.at(span),
                                     "reaching this expression at runtime will panic or abort",
                                     tcx.hir().local_def_id_to_hir_id(def.did),
                                     Some(err.span),
                                 ))
                             }
                         // anything else (array lengths, enum initializers, constant patterns) are
                         // reported as hard errors
                         } else {
                             Err(err.report_as_error(
                                 ecx.tcx.at(ecx.cur_span()),
                                 "evaluation of constant value failed",
                             ))
                         }
                     }
                 }
             } else {
                 // use of broken constant from other crate
                 Err(err.report_as_error(ecx.tcx.at(ecx.cur_span()), "could not evaluate constant"))
             }
         }
         Ok(mplace) => {
             // Since evaluation had no errors, valiate the resulting constant:
             let validation = try {
                 // 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,
                         )?;
                     }
                 }
             };
             if let Err(error) = validation {
                 // Validation failed, report an error
                 let err = ConstEvalErr::new(&ecx, error, None);
                 Err(err.struct_error(
                     ecx.tcx,
                     "it is undefined behavior to use this value",
                     |mut diag| {
                         diag.note(note_on_undefined_behavior_error());
                         diag.emit();
                     },
                 ))
             } else {
                 // Convert to raw constant
                 Ok(ConstAlloc { alloc_id: mplace.ptr.assert_ptr().alloc_id, ty: mplace.layout.ty })
             }
         }
     }
 }
	use super::{CompileTimeEvalContext, CompileTimeInterpreter, ConstEvalErr, MemoryExtra};
	use crate::interpret::eval_nullary_intrinsic;
	use crate::interpret::{
	intern_const_alloc_recursive, Allocation, ConstAlloc, ConstValue, GlobalId, Immediate,
	InternKind, InterpCx, InterpResult, MPlaceTy, MemoryKind, OpTy, RefTracking, Scalar,
	ScalarMaybeUninit, StackPopCleanup,
	};

	use rustc_hir::def::DefKind;
	use rustc_middle::mir;
	use rustc_middle::mir::interpret::ErrorHandled;
	use rustc_middle::traits::Reveal;
	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::{Abi, LayoutOf};
	use std::convert::{TryFrom, 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 =
	with_no_trimmed_paths(\|\| 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
	// FIXME: since the DefId of a promoted is the DefId of its owner, this
	// means that promoteds in statics are actually interned like statics!
	// However, this is also currently crucial because we promote mutable
	// non-empty slices in statics to extend their lifetime, and this
	// ensures that they are put into a mutable allocation.
	// For other kinds of promoteds in statics (like array initializers), this is rather silly.
	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 },
	)
	}

	/// This function converts an interpreter value into a constant that is meant for use in the
	/// type system.
	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!(
	u64::try_from(data).unwrap() % mplace.layout.align.abi.bytes(),
	0,
	"this MPlaceTy must come from a validated constant, thus we can assume the \
	alignment is correct",
	);
	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.check_init().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 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.
	op_to_const(&ecx, mplace.into())
	}

	pub fn eval_to_const_value_raw_provider<'tcx>(
	tcx: TyCtxt<'tcx>,
	key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
	) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'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.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 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.eval_to_allocation_raw(key).map(\|val\| turn_into_const_value(tcx, val, key))
	}

	pub fn eval_to_allocation_raw_provider<'tcx>(
	tcx: TyCtxt<'tcx>,
	key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>,
	) -> ::rustc_middle::mir::interpret::EvalToAllocationRawResult<'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.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();

	if let Some(def) = def.as_local() {
	if tcx.has_typeck_results(def.did) {
	if let Some(error_reported) = tcx.typeck_opt_const_arg(def).tainted_by_errors {
	return Err(ErrorHandled::Reported(error_reported));
	}
	}
	}

	let is_static = tcx.is_static(def.did);

	let mut ecx = InterpCx::new(
	tcx,
	tcx.def_span(def.did),
	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);
	match res.and_then(\|body\| eval_body_using_ecx(&mut ecx, cid, &body)) {
	Err(error) => {
	let err = ConstEvalErr::new(&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),
	);
	}

	Err(v)
	} else if let Some(def) = def.as_local() {
	// constant defined in this crate, we can figure out a lint level!
	match tcx.def_kind(def.did.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().local_def_id_to_hir_id(def.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),
	))
	}
	// 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_opt_const_arg(def.to_global())[p].span;
	if let err_inval!(ReferencedConstant) = err.error {
	Err(err.report_as_error(
	tcx.at(span),
	"evaluation of constant expression failed",
	))
	} else {
	Err(err.report_as_lint(
	tcx.at(span),
	"reaching this expression at runtime will panic or abort",
	tcx.hir().local_def_id_to_hir_id(def.did),
	Some(err.span),
	))
	}
	// anything else (array lengths, enum initializers, constant patterns) are
	// reported as hard errors
	} else {
	Err(err.report_as_error(
	ecx.tcx.at(ecx.cur_span()),
	"evaluation of constant value failed",
	))
	}
	}
	}
	} else {
	// use of broken constant from other crate
	Err(err.report_as_error(ecx.tcx.at(ecx.cur_span()), "could not evaluate constant"))
	}
	}
	Ok(mplace) => {
	// Since evaluation had no errors, valiate the resulting constant:
	let validation = try {
	// 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,
	)?;
	}
	}
	};
	if let Err(error) = validation {
	// Validation failed, report an error
	let err = ConstEvalErr::new(&ecx, error, None);
	Err(err.struct_error(
	ecx.tcx,
	"it is undefined behavior to use this value",
	\|mut diag\| {
	diag.note(note_on_undefined_behavior_error());
	diag.emit();
	},
	))
	} else {
	// Convert to raw constant
	Ok(ConstAlloc { alloc_id: mplace.ptr.assert_ptr().alloc_id, ty: mplace.layout.ty })
	}
	}
	}
	}