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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::{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().subst(tcx, cid.instance.substs))?;
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.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: bool,
) -> 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,
/*can_access_statics:*/ 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> {
assert!(key.param_env.is_const());
// see comment in eval_to_allocation_raw_provider for what we're doing here
if key.param_env.reveal() == Reveal::All {
let mut key = key;
key.param_env = key.param_env.with_user_facing();
match tcx.eval_to_const_value_raw(key) {
// try again with reveal all as requested
Err(ErrorHandled::TooGeneric) => {}
// deduplicate calls
other => return other,
}
}
// We call `const_eval` for zero arg intrinsics, too, in order to cache their value.
// Catch such calls and evaluate them instead of trying to load a constant's MIR.
if let ty::InstanceDef::Intrinsic(def_id) = key.value.instance.def {
let ty = key.value.instance.ty(tcx, key.param_env);
let ty::FnDef(_, substs) = ty.kind() else {
bug!("intrinsic with type {:?}", ty);
};
return eval_nullary_intrinsic(tcx, key.param_env, def_id, substs).map_err(|error| {
let span = tcx.def_span(def_id);
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> {
assert!(key.param_env.is_const());
// Because the constant is computed twice (once per value of `Reveal`), we are at risk of
// reporting the same error twice here. To resolve this, we check whether we can evaluate the
// constant in the more restrictive `Reveal::UserFacing`, which most likely already was
// computed. For a large percentage of constants that will already have succeeded. Only
// associated constants of generic functions will fail due to not enough monomorphization
// information being available.
// In case we fail in the `UserFacing` variant, we just do the real computation.
if key.param_env.reveal() == Reveal::All {
let mut key = key;
key.param_env = key.param_env.with_user_facing();
match tcx.eval_to_allocation_raw(key) {
// try again with reveal all as requested
Err(ErrorHandled::TooGeneric) => {}
// deduplicate calls
other => return other,
}
}
if cfg!(debug_assertions) {
// Make sure we format the instance even if we do not print it.
// This serves as a regression test against an ICE on printing.
// The next two lines concatenated contain some discussion:
// https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
// subject/anon_const_instance_printing/near/135980032
let instance = with_no_trimmed_paths!(key.value.instance.to_string());
trace!("const eval: {:?} ({})", key, instance);
}
let cid = key.value;
let def = cid.instance.def.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(
/*can_access_statics:*/ 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 substs: to show the actual compile-time values, in addition to
// the expression, leading to the const eval error.
let instance = &key.value.instance;
if !instance.substs.is_empty() {
let instance = with_no_trimmed_paths!(instance.to_string());
("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);
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 })
}
}
}
}