compiler/rustc_const_eval/src/const_eval/eval_queries.rs - toolchain/rustc - Git at Google

 use crate::const_eval::CheckAlignment;
 use crate::errors::ConstEvalError;

 use either::{Left, Right};

 use rustc_hir::def::DefKind;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::{ErrorHandled, InterpErrorInfo};
 use rustc_middle::mir::pretty::write_allocation_bytes;
 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, TyCtxt};
 use rustc_span::source_map::Span;
 use rustc_target::abi::{self, Abi};

 use super::{CanAccessStatics, CompileTimeEvalContext, CompileTimeInterpreter};
 use crate::errors;
 use crate::interpret::eval_nullary_intrinsic;
 use crate::interpret::{
     intern_const_alloc_recursive, Allocation, ConstAlloc, ConstValue, CtfeValidationMode, GlobalId,
     Immediate, InternKind, InterpCx, InterpError, InterpResult, MPlaceTy, MemoryKind, OpTy,
     RefTracking, StackPopCleanup,
 };

 // 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().instantiate(tcx, cid.instance.args))?;
     assert!(layout.is_sized());
     let ret = ecx.allocate(layout, MemoryKind::Stack)?;

     trace!(
         "eval_body_using_ecx: pushing stack frame for global: {}{}",
         with_no_trimmed_paths!(ecx.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.clone().into(),
         StackPopCleanup::Root { cleanup: false },
     )?;

     // The main interpreter loop.
     while ecx.step()? {}

     // 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,
         }
     };
     ecx.machine.check_alignment = CheckAlignment::No; // interning doesn't need to respect alignment
     intern_const_alloc_recursive(ecx, intern_kind, &ret)?;
     // we leave alignment checks off, since this `ecx` will not be used for further evaluation anyway

     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. It never performs alignment checks.
 ///
 /// 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: CanAccessStatics,
 ) -> CompileTimeEvalContext<'mir, 'tcx> {
     debug!("mk_eval_cx: {:?}", param_env);
     InterpCx::new(
         tcx,
         root_span,
         param_env,
         CompileTimeInterpreter::new(can_access_statics, CheckAlignment::No),
     )
 }

 /// 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 {
         Right(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.as_mplace_or_imm()
     };

     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 {
         Left(ref mplace) => to_const_value(mplace),
         // see comment on `let try_as_immediate` above
         Right(imm) => match *imm {
             _ if imm.layout.is_zst() => ConstValue::ZeroSized,
             Immediate::Scalar(x) => ConstValue::Scalar(x),
             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.mk_const_alloc(Allocation::from_bytes_byte_aligned_immutable(
                             b"" as &[u8],
                         )),
                         0,
                     ),
                 };
                 let len = b.to_target_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", ret)]
 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);
     // This is just accessing an already computed constant, so no need to check alignment here.
     let ecx = mk_eval_cx(
         tcx,
         tcx.def_span(key.value.instance.def_id()),
         key.param_env,
         CanAccessStatics::from(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())
 }

 #[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> {
     // 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(_, args) = ty.kind() else {
             bug!("intrinsic with type {:?}", ty);
         };
         return eval_nullary_intrinsic(tcx, key.param_env, def_id, args).map_err(|error| {
             let span = tcx.def_span(def_id);

             super::report(
                 tcx,
                 error.into_kind(),
                 Some(span),
                 || (span, vec![]),
                 |span, _| errors::NullaryIntrinsicError { span },
             )
         });
     }

     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> {
     // 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.def_id();
     let is_static = tcx.is_static(def);

     let mut ecx = InterpCx::new(
         tcx,
         tcx.def_span(def),
         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(
             CanAccessStatics::from(is_static),
             if tcx.sess.opts.unstable_opts.extra_const_ub_checks {
                 CheckAlignment::Error
             } else {
                 CheckAlignment::FutureIncompat
             },
         ),
     );

     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 (error, backtrace) = error.into_parts();
             backtrace.print_backtrace();

             let (kind, instance) = if is_static {
                 ("static", String::new())
             } else {
                 // If the current item has generics, we'd like to enrich the message with the
                 // instance and its args: 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.args.is_empty() {
                     let instance = with_no_trimmed_paths!(instance.to_string());
                     ("const_with_path", instance)
                 } else {
                     ("const", String::new())
                 }
             };

             Err(super::report(
                 *ecx.tcx,
                 error,
                 None,
                 || super::get_span_and_frames(&ecx),
                 |span, frames| ConstEvalError {
                     span,
                     error_kind: kind,
                     instance,
                     frame_notes: frames,
                 },
             ))
         }
         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: Result<_, InterpErrorInfo<'_>> = try {
                 let mut ref_tracking = RefTracking::new(mplace.clone());
                 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();

             // Validation failed, report an error. This is always a hard error.
             if let Err(error) = validation {
                 let (error, backtrace) = error.into_parts();
                 backtrace.print_backtrace();

                 let ub_note = matches!(error, InterpError::UndefinedBehavior(_)).then(|| {});

                 let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory().inner();
                 let mut bytes = String::new();
                 if alloc.size() != abi::Size::ZERO {
                     bytes = "\n".into();
                     // FIXME(translation) there might be pieces that are translatable.
                     write_allocation_bytes(*ecx.tcx, alloc, &mut bytes, "    ").unwrap();
                 }
                 let raw_bytes = errors::RawBytesNote {
                     size: alloc.size().bytes(),
                     align: alloc.align.bytes(),
                     bytes,
                 };

                 Err(super::report(
                     *ecx.tcx,
                     error,
                     None,
                     || super::get_span_and_frames(&ecx),
                     move |span, frames| errors::UndefinedBehavior {
                         span,
                         ub_note,
                         frames,
                         raw_bytes,
                     },
                 ))
             } else {
                 // Convert to raw constant
                 Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })
             }
         }
     }
 }
	use crate::const_eval::CheckAlignment;
	use crate::errors::ConstEvalError;

	use either::{Left, Right};

	use rustc_hir::def::DefKind;
	use rustc_middle::mir;
	use rustc_middle::mir::interpret::{ErrorHandled, InterpErrorInfo};
	use rustc_middle::mir::pretty::write_allocation_bytes;
	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, TyCtxt};
	use rustc_span::source_map::Span;
	use rustc_target::abi::{self, Abi};

	use super::{CanAccessStatics, CompileTimeEvalContext, CompileTimeInterpreter};
	use crate::errors;
	use crate::interpret::eval_nullary_intrinsic;
	use crate::interpret::{
	intern_const_alloc_recursive, Allocation, ConstAlloc, ConstValue, CtfeValidationMode, GlobalId,
	Immediate, InternKind, InterpCx, InterpError, InterpResult, MPlaceTy, MemoryKind, OpTy,
	RefTracking, StackPopCleanup,
	};

	// 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().instantiate(tcx, cid.instance.args))?;
	assert!(layout.is_sized());
	let ret = ecx.allocate(layout, MemoryKind::Stack)?;

	trace!(
	"eval_body_using_ecx: pushing stack frame for global: {}{}",
	with_no_trimmed_paths!(ecx.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.clone().into(),
	StackPopCleanup::Root { cleanup: false },
	)?;

	// The main interpreter loop.
	while ecx.step()? {}

	// 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,
	}
	};
	ecx.machine.check_alignment = CheckAlignment::No; // interning doesn't need to respect alignment
	intern_const_alloc_recursive(ecx, intern_kind, &ret)?;
	// we leave alignment checks off, since this `ecx` will not be used for further evaluation anyway

	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. It never performs alignment checks.
	///
	/// 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: CanAccessStatics,
	) -> CompileTimeEvalContext<'mir, 'tcx> {
	debug!("mk_eval_cx: {:?}", param_env);
	InterpCx::new(
	tcx,
	root_span,
	param_env,
	CompileTimeInterpreter::new(can_access_statics, CheckAlignment::No),
	)
	}

	/// 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 {
	Right(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.as_mplace_or_imm()
	};

	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 {
	Left(ref mplace) => to_const_value(mplace),
	// see comment on `let try_as_immediate` above
	Right(imm) => match *imm {
	_ if imm.layout.is_zst() => ConstValue::ZeroSized,
	Immediate::Scalar(x) => ConstValue::Scalar(x),
	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.mk_const_alloc(Allocation::from_bytes_byte_aligned_immutable(
	b"" as &[u8],
	)),
	0,
	),
	};
	let len = b.to_target_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", ret)]
	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);
	// This is just accessing an already computed constant, so no need to check alignment here.
	let ecx = mk_eval_cx(
	tcx,
	tcx.def_span(key.value.instance.def_id()),
	key.param_env,
	CanAccessStatics::from(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())
	}

	#[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> {
	// 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(_, args) = ty.kind() else {
	bug!("intrinsic with type {:?}", ty);
	};
	return eval_nullary_intrinsic(tcx, key.param_env, def_id, args).map_err(\|error\| {
	let span = tcx.def_span(def_id);

	super::report(
	tcx,
	error.into_kind(),
	Some(span),
	\|\| (span, vec![]),
	\|span, _\| errors::NullaryIntrinsicError { span },
	)
	});
	}

	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> {
	// 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.def_id();
	let is_static = tcx.is_static(def);

	let mut ecx = InterpCx::new(
	tcx,
	tcx.def_span(def),
	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(
	CanAccessStatics::from(is_static),
	if tcx.sess.opts.unstable_opts.extra_const_ub_checks {
	CheckAlignment::Error
	} else {
	CheckAlignment::FutureIncompat
	},
	),
	);

	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 (error, backtrace) = error.into_parts();
	backtrace.print_backtrace();

	let (kind, instance) = if is_static {
	("static", String::new())
	} else {
	// If the current item has generics, we'd like to enrich the message with the
	// instance and its args: 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.args.is_empty() {
	let instance = with_no_trimmed_paths!(instance.to_string());
	("const_with_path", instance)
	} else {
	("const", String::new())
	}
	};

	Err(super::report(
	*ecx.tcx,
	error,
	None,
	\|\| super::get_span_and_frames(&ecx),
	\|span, frames\| ConstEvalError {
	span,
	error_kind: kind,
	instance,
	frame_notes: frames,
	},
	))
	}
	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: Result<_, InterpErrorInfo<'_>> = try {
	let mut ref_tracking = RefTracking::new(mplace.clone());
	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();

	// Validation failed, report an error. This is always a hard error.
	if let Err(error) = validation {
	let (error, backtrace) = error.into_parts();
	backtrace.print_backtrace();

	let ub_note = matches!(error, InterpError::UndefinedBehavior(_)).then(\|\| {});

	let alloc = ecx.tcx.global_alloc(alloc_id).unwrap_memory().inner();
	let mut bytes = String::new();
	if alloc.size() != abi::Size::ZERO {
	bytes = "\n".into();
	// FIXME(translation) there might be pieces that are translatable.
	write_allocation_bytes(*ecx.tcx, alloc, &mut bytes, " ").unwrap();
	}
	let raw_bytes = errors::RawBytesNote {
	size: alloc.size().bytes(),
	align: alloc.align.bytes(),
	bytes,
	};

	Err(super::report(
	*ecx.tcx,
	error,
	None,
	\|\| super::get_span_and_frames(&ecx),
	move \|span, frames\| errors::UndefinedBehavior {
	span,
	ub_note,
	frames,
	raw_bytes,
	},
	))
	} else {
	// Convert to raw constant
	Ok(ConstAlloc { alloc_id, ty: mplace.layout.ty })
	}
	}
	}
	}