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use std::fmt::{self, Debug, Display, Formatter};
use rustc_hir;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::{self as hir};
use rustc_span::Span;
use rustc_target::abi::{HasDataLayout, Size};
use crate::mir::interpret::{alloc_range, AllocId, ConstAllocation, ErrorHandled, Scalar};
use crate::mir::{pretty_print_const_value, Promoted};
use crate::ty::ScalarInt;
use crate::ty::{self, print::pretty_print_const, List, Ty, TyCtxt};
use crate::ty::{GenericArgs, GenericArgsRef};
///////////////////////////////////////////////////////////////////////////
/// Evaluated Constants
/// Represents the result of const evaluation via the `eval_to_allocation` query.
/// Not to be confused with `ConstAllocation`, which directly refers to the underlying data!
/// Here we indirect via an `AllocId`.
#[derive(Copy, Clone, HashStable, TyEncodable, TyDecodable, Debug, Hash, Eq, PartialEq)]
pub struct ConstAlloc<'tcx> {
/// The value lives here, at offset 0, and that allocation definitely is an `AllocKind::Memory`
/// (so you can use `AllocMap::unwrap_memory`).
pub alloc_id: AllocId,
pub ty: Ty<'tcx>,
}
/// Represents a constant value in Rust. `Scalar` and `Slice` are optimizations for
/// array length computations, enum discriminants and the pattern matching logic.
#[derive(Copy, Clone, Debug, Eq, PartialEq, TyEncodable, TyDecodable, Hash)]
#[derive(HashStable, Lift)]
pub enum ConstValue<'tcx> {
/// Used for types with `layout::abi::Scalar` ABI.
///
/// Not using the enum `Value` to encode that this must not be `Uninit`.
Scalar(Scalar),
/// Only for ZSTs.
ZeroSized,
/// Used for references to unsized types with slice tail.
///
/// This is worth an optimized representation since Rust has literals of type `&str` and
/// `&[u8]`. Not having to indirect those through an `AllocId` (or two, if we used `Indirect`)
/// has shown measurable performance improvements on stress tests. We then reuse this
/// optimization for slice-tail types more generally during valtree-to-constval conversion.
Slice {
/// The allocation storing the slice contents.
/// This always points to the beginning of the allocation.
data: ConstAllocation<'tcx>,
/// The metadata field of the reference.
/// This is a "target usize", so we use `u64` as in the interpreter.
meta: u64,
},
/// A value not representable by the other variants; needs to be stored in-memory.
///
/// Must *not* be used for scalars or ZST, but having `&str` or other slices in this variant is fine.
Indirect {
/// The backing memory of the value. May contain more memory than needed for just the value
/// if this points into some other larger ConstValue.
///
/// We use an `AllocId` here instead of a `ConstAllocation<'tcx>` to make sure that when a
/// raw constant (which is basically just an `AllocId`) is turned into a `ConstValue` and
/// back, we can preserve the original `AllocId`.
alloc_id: AllocId,
/// Offset into `alloc`
offset: Size,
},
}
#[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
static_assert_size!(ConstValue<'_>, 24);
impl<'tcx> ConstValue<'tcx> {
#[inline]
pub fn try_to_scalar(&self) -> Option<Scalar<AllocId>> {
match *self {
ConstValue::Indirect { .. } | ConstValue::Slice { .. } | ConstValue::ZeroSized => None,
ConstValue::Scalar(val) => Some(val),
}
}
pub fn try_to_scalar_int(&self) -> Option<ScalarInt> {
self.try_to_scalar()?.try_to_int().ok()
}
pub fn try_to_bits(&self, size: Size) -> Option<u128> {
self.try_to_scalar_int()?.to_bits(size).ok()
}
pub fn try_to_bool(&self) -> Option<bool> {
self.try_to_scalar_int()?.try_into().ok()
}
pub fn try_to_target_usize(&self, tcx: TyCtxt<'tcx>) -> Option<u64> {
self.try_to_scalar_int()?.try_to_target_usize(tcx).ok()
}
pub fn try_to_bits_for_ty(
&self,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
ty: Ty<'tcx>,
) -> Option<u128> {
let size = tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(ty)).ok()?.size;
self.try_to_bits(size)
}
pub fn from_bool(b: bool) -> Self {
ConstValue::Scalar(Scalar::from_bool(b))
}
pub fn from_u64(i: u64) -> Self {
ConstValue::Scalar(Scalar::from_u64(i))
}
pub fn from_u128(i: u128) -> Self {
ConstValue::Scalar(Scalar::from_u128(i))
}
pub fn from_target_usize(i: u64, cx: &impl HasDataLayout) -> Self {
ConstValue::Scalar(Scalar::from_target_usize(i, cx))
}
/// Must only be called on constants of type `&str` or `&[u8]`!
pub fn try_get_slice_bytes_for_diagnostics(&self, tcx: TyCtxt<'tcx>) -> Option<&'tcx [u8]> {
let (data, start, end) = match self {
ConstValue::Scalar(_) | ConstValue::ZeroSized => {
bug!("`try_get_slice_bytes` on non-slice constant")
}
&ConstValue::Slice { data, meta } => (data, 0, meta),
&ConstValue::Indirect { alloc_id, offset } => {
// The reference itself is stored behind an indirection.
// Load the reference, and then load the actual slice contents.
let a = tcx.global_alloc(alloc_id).unwrap_memory().inner();
let ptr_size = tcx.data_layout.pointer_size;
if a.size() < offset + 2 * ptr_size {
// (partially) dangling reference
return None;
}
// Read the wide pointer components.
let ptr = a
.read_scalar(
&tcx,
alloc_range(offset, ptr_size),
/* read_provenance */ true,
)
.ok()?;
let ptr = ptr.to_pointer(&tcx).ok()?;
let len = a
.read_scalar(
&tcx,
alloc_range(offset + ptr_size, ptr_size),
/* read_provenance */ false,
)
.ok()?;
let len = len.to_target_usize(&tcx).ok()?;
if len == 0 {
return Some(&[]);
}
// Non-empty slice, must have memory. We know this is a relative pointer.
let (inner_alloc_id, offset) = ptr.into_parts();
let data = tcx.global_alloc(inner_alloc_id?).unwrap_memory();
(data, offset.bytes(), offset.bytes() + len)
}
};
// This is for diagnostics only, so we are okay to use `inspect_with_uninit_and_ptr_outside_interpreter`.
let start = start.try_into().unwrap();
let end = end.try_into().unwrap();
Some(data.inner().inspect_with_uninit_and_ptr_outside_interpreter(start..end))
}
}
///////////////////////////////////////////////////////////////////////////
/// Constants
#[derive(Clone, Copy, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable, Debug)]
#[derive(TypeFoldable, TypeVisitable)]
pub enum Const<'tcx> {
/// This constant came from the type system.
///
/// Any way of turning `ty::Const` into `ConstValue` should go through `valtree_to_const_val`;
/// this ensures that we consistently produce "clean" values without data in the padding or
/// anything like that.
Ty(ty::Const<'tcx>),
/// An unevaluated mir constant which is not part of the type system.
///
/// Note that `Ty(ty::ConstKind::Unevaluated)` and this variant are *not* identical! `Ty` will
/// always flow through a valtree, so all data not captured in the valtree is lost. This variant
/// directly uses the evaluated result of the given constant, including e.g. data stored in
/// padding.
Unevaluated(UnevaluatedConst<'tcx>, Ty<'tcx>),
/// This constant cannot go back into the type system, as it represents
/// something the type system cannot handle (e.g. pointers).
Val(ConstValue<'tcx>, Ty<'tcx>),
}
impl<'tcx> Const<'tcx> {
#[inline(always)]
pub fn ty(&self) -> Ty<'tcx> {
match self {
Const::Ty(c) => c.ty(),
Const::Val(_, ty) | Const::Unevaluated(_, ty) => *ty,
}
}
#[inline]
pub fn try_to_scalar(self) -> Option<Scalar> {
match self {
Const::Ty(c) => match c.kind() {
ty::ConstKind::Value(valtree) => match valtree {
ty::ValTree::Leaf(scalar_int) => Some(Scalar::Int(scalar_int)),
ty::ValTree::Branch(_) => None,
},
_ => None,
},
Const::Val(val, _) => val.try_to_scalar(),
Const::Unevaluated(..) => None,
}
}
#[inline]
pub fn try_to_scalar_int(self) -> Option<ScalarInt> {
self.try_to_scalar()?.try_to_int().ok()
}
#[inline]
pub fn try_to_bits(self, size: Size) -> Option<u128> {
self.try_to_scalar_int()?.to_bits(size).ok()
}
#[inline]
pub fn try_to_bool(self) -> Option<bool> {
self.try_to_scalar_int()?.try_into().ok()
}
#[inline]
pub fn eval(
self,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
span: Option<Span>,
) -> Result<ConstValue<'tcx>, ErrorHandled> {
match self {
Const::Ty(c) => {
// We want to consistently have a "clean" value for type system constants (i.e., no
// data hidden in the padding), so we always go through a valtree here.
let val = c.eval(tcx, param_env, span)?;
Ok(tcx.valtree_to_const_val((self.ty(), val)))
}
Const::Unevaluated(uneval, _) => {
// FIXME: We might want to have a `try_eval`-like function on `Unevaluated`
tcx.const_eval_resolve(param_env, uneval, span)
}
Const::Val(val, _) => Ok(val),
}
}
/// Normalizes the constant to a value or an error if possible.
#[inline]
pub fn normalize(self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Self {
match self.eval(tcx, param_env, None) {
Ok(val) => Self::Val(val, self.ty()),
Err(ErrorHandled::Reported(guar, _span)) => {
Self::Ty(ty::Const::new_error(tcx, guar.into(), self.ty()))
}
Err(ErrorHandled::TooGeneric(_span)) => self,
}
}
#[inline]
pub fn try_eval_scalar(
self,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Option<Scalar> {
self.eval(tcx, param_env, None).ok()?.try_to_scalar()
}
#[inline]
pub fn try_eval_scalar_int(
self,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Option<ScalarInt> {
match self {
// If the constant is already evaluated, we shortcut here.
Const::Ty(c) if let ty::ConstKind::Value(valtree) = c.kind() => {
valtree.try_to_scalar_int()
},
// This is a more general form of the previous case.
_ => {
self.try_eval_scalar(tcx, param_env)?.try_to_int().ok()
},
}
}
#[inline]
pub fn try_eval_bits(&self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Option<u128> {
let int = self.try_eval_scalar_int(tcx, param_env)?;
let size =
tcx.layout_of(param_env.with_reveal_all_normalized(tcx).and(self.ty())).ok()?.size;
int.to_bits(size).ok()
}
/// Panics if the value cannot be evaluated or doesn't contain a valid integer of the given type.
#[inline]
pub fn eval_bits(self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> u128 {
self.try_eval_bits(tcx, param_env)
.unwrap_or_else(|| bug!("expected bits of {:#?}, got {:#?}", self.ty(), self))
}
#[inline]
pub fn try_eval_target_usize(
self,
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
) -> Option<u64> {
self.try_eval_scalar_int(tcx, param_env)?.try_to_target_usize(tcx).ok()
}
#[inline]
/// Panics if the value cannot be evaluated or doesn't contain a valid `usize`.
pub fn eval_target_usize(self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> u64 {
self.try_eval_target_usize(tcx, param_env)
.unwrap_or_else(|| bug!("expected usize, got {:#?}", self))
}
#[inline]
pub fn try_eval_bool(self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Option<bool> {
self.try_eval_scalar_int(tcx, param_env)?.try_into().ok()
}
#[inline]
pub fn from_value(val: ConstValue<'tcx>, ty: Ty<'tcx>) -> Self {
Self::Val(val, ty)
}
pub fn from_bits(
tcx: TyCtxt<'tcx>,
bits: u128,
param_env_ty: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
) -> Self {
let size = tcx
.layout_of(param_env_ty)
.unwrap_or_else(|e| {
bug!("could not compute layout for {:?}: {:?}", param_env_ty.value, e)
})
.size;
let cv = ConstValue::Scalar(Scalar::from_uint(bits, size));
Self::Val(cv, param_env_ty.value)
}
#[inline]
pub fn from_bool(tcx: TyCtxt<'tcx>, v: bool) -> Self {
let cv = ConstValue::from_bool(v);
Self::Val(cv, tcx.types.bool)
}
#[inline]
pub fn zero_sized(ty: Ty<'tcx>) -> Self {
let cv = ConstValue::ZeroSized;
Self::Val(cv, ty)
}
pub fn from_usize(tcx: TyCtxt<'tcx>, n: u64) -> Self {
let ty = tcx.types.usize;
Self::from_bits(tcx, n as u128, ty::ParamEnv::empty().and(ty))
}
#[inline]
pub fn from_scalar(_tcx: TyCtxt<'tcx>, s: Scalar, ty: Ty<'tcx>) -> Self {
let val = ConstValue::Scalar(s);
Self::Val(val, ty)
}
/// Literals are converted to `Const::Val`, const generic parameters are eagerly
/// converted to a constant, everything else becomes `Unevaluated`.
#[instrument(skip(tcx), level = "debug", ret)]
pub fn from_anon_const(
tcx: TyCtxt<'tcx>,
def: LocalDefId,
param_env: ty::ParamEnv<'tcx>,
) -> Self {
let body_id = match tcx.hir().get_by_def_id(def) {
hir::Node::AnonConst(ac) => ac.body,
_ => {
span_bug!(tcx.def_span(def), "from_anon_const can only process anonymous constants")
}
};
let expr = &tcx.hir().body(body_id).value;
debug!(?expr);
// Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
// currently have to be wrapped in curly brackets, so it's necessary to special-case.
let expr = match &expr.kind {
hir::ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
block.expr.as_ref().unwrap()
}
_ => expr,
};
debug!("expr.kind: {:?}", expr.kind);
let ty = tcx.type_of(def).instantiate_identity();
debug!(?ty);
// FIXME(const_generics): We currently have to special case parameters because `min_const_generics`
// does not provide the parents generics to anonymous constants. We still allow generic const
// parameters by themselves however, e.g. `N`. These constants would cause an ICE if we were to
// ever try to substitute the generic parameters in their bodies.
//
// While this doesn't happen as these constants are always used as `ty::ConstKind::Param`, it does
// cause issues if we were to remove that special-case and try to evaluate the constant instead.
use hir::{def::DefKind::ConstParam, def::Res, ExprKind, Path, QPath};
match expr.kind {
ExprKind::Path(QPath::Resolved(_, &Path { res: Res::Def(ConstParam, def_id), .. })) => {
// Find the name and index of the const parameter by indexing the generics of
// the parent item and construct a `ParamConst`.
let item_def_id = tcx.parent(def_id);
let generics = tcx.generics_of(item_def_id);
let index = generics.param_def_id_to_index[&def_id];
let name = tcx.item_name(def_id);
let ty_const = ty::Const::new_param(tcx, ty::ParamConst::new(index, name), ty);
debug!(?ty_const);
return Self::Ty(ty_const);
}
_ => {}
}
let hir_id = tcx.hir().local_def_id_to_hir_id(def);
let parent_args = if let Some(parent_hir_id) = tcx.hir().opt_parent_id(hir_id)
&& let Some(parent_did) = parent_hir_id.as_owner()
{
GenericArgs::identity_for_item(tcx, parent_did)
} else {
List::empty()
};
debug!(?parent_args);
let did = def.to_def_id();
let child_args = GenericArgs::identity_for_item(tcx, did);
let args = tcx.mk_args_from_iter(parent_args.into_iter().chain(child_args.into_iter()));
debug!(?args);
let span = tcx.def_span(def);
let uneval = UnevaluatedConst::new(did, args);
debug!(?span, ?param_env);
match tcx.const_eval_resolve(param_env, uneval, Some(span)) {
Ok(val) => {
debug!("evaluated const value");
Self::Val(val, ty)
}
Err(_) => {
debug!("error encountered during evaluation");
// Error was handled in `const_eval_resolve`. Here we just create a
// new unevaluated const and error hard later in codegen
Self::Unevaluated(
UnevaluatedConst {
def: did,
args: GenericArgs::identity_for_item(tcx, did),
promoted: None,
},
ty,
)
}
}
}
pub fn from_ty_const(c: ty::Const<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
match c.kind() {
ty::ConstKind::Value(valtree) => {
// Make sure that if `c` is normalized, then the return value is normalized.
let const_val = tcx.valtree_to_const_val((c.ty(), valtree));
Self::Val(const_val, c.ty())
}
_ => Self::Ty(c),
}
}
}
/// An unevaluated (potentially generic) constant used in MIR.
#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)]
#[derive(Hash, HashStable, TypeFoldable, TypeVisitable)]
pub struct UnevaluatedConst<'tcx> {
pub def: DefId,
pub args: GenericArgsRef<'tcx>,
pub promoted: Option<Promoted>,
}
impl<'tcx> UnevaluatedConst<'tcx> {
#[inline]
pub fn shrink(self) -> ty::UnevaluatedConst<'tcx> {
assert_eq!(self.promoted, None);
ty::UnevaluatedConst { def: self.def, args: self.args }
}
}
impl<'tcx> UnevaluatedConst<'tcx> {
#[inline]
pub fn new(def: DefId, args: GenericArgsRef<'tcx>) -> UnevaluatedConst<'tcx> {
UnevaluatedConst { def, args, promoted: Default::default() }
}
#[inline]
pub fn from_instance(instance: ty::Instance<'tcx>) -> Self {
UnevaluatedConst::new(instance.def_id(), instance.args)
}
}
impl<'tcx> Display for Const<'tcx> {
fn fmt(&self, fmt: &mut Formatter<'_>) -> fmt::Result {
match *self {
Const::Ty(c) => pretty_print_const(c, fmt, true),
Const::Val(val, ty) => pretty_print_const_value(val, ty, fmt),
// FIXME(valtrees): Correctly print mir constants.
Const::Unevaluated(..) => {
fmt.write_str("_")?;
Ok(())
}
}
}
}