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Auto merge of #115804 - RalfJung:valtree-to-const-val, r=oli-obk
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consistently pass ty::Const through valtrees

Some drive-by things extracted from #115748.
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@bors
bors committed Sep 14, 2023
2 parents 5e71913 + 19fb2c7 commit e437e57
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Showing 4 changed files with 78 additions and 106 deletions.
103 changes: 52 additions & 51 deletions compiler/rustc_const_eval/src/const_eval/valtrees.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ use crate::interpret::{
intern_const_alloc_recursive, ConstValue, ImmTy, Immediate, InternKind, MemPlaceMeta,
MemoryKind, PlaceTy, Projectable, Scalar,
};
use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
use rustc_middle::ty::layout::{LayoutCx, LayoutOf, TyAndLayout};
use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt};
use rustc_span::source_map::DUMMY_SP;
use rustc_target::abi::VariantIdx;
Expand Down Expand Up @@ -189,12 +189,11 @@ fn reconstruct_place_meta<'tcx>(
}

#[instrument(skip(ecx), level = "debug", ret)]
fn create_pointee_place<'tcx>(
fn create_valtree_place<'tcx>(
ecx: &mut CompileTimeEvalContext<'tcx, 'tcx>,
ty: Ty<'tcx>,
layout: TyAndLayout<'tcx>,
valtree: ty::ValTree<'tcx>,
) -> MPlaceTy<'tcx> {
let layout = ecx.layout_of(ty).unwrap();
let meta = reconstruct_place_meta(layout, valtree, ecx.tcx.tcx);
ecx.allocate_dyn(layout, MemoryKind::Stack, meta).unwrap()
}
Expand All @@ -216,11 +215,6 @@ pub fn valtree_to_const_value<'tcx>(
// FIXME Does this need an example?

let (param_env, ty) = param_env_ty.into_parts();
let mut ecx: crate::interpret::InterpCx<
'_,
'_,
crate::const_eval::CompileTimeInterpreter<'_, '_>,
> = mk_eval_cx(tcx, DUMMY_SP, param_env, CanAccessStatics::No);

match ty.kind() {
ty::FnDef(..) => {
Expand All @@ -233,33 +227,44 @@ pub fn valtree_to_const_value<'tcx>(
"ValTrees for Bool, Int, Uint, Float or Char should have the form ValTree::Leaf"
),
},
ty::Ref(_, _, _) | ty::Tuple(_) | ty::Array(_, _) | ty::Adt(..) => {
let place = match ty.kind() {
ty::Ref(_, inner_ty, _) => {
// Need to create a place for the pointee (the reference itself will be an immediate)
create_pointee_place(&mut ecx, *inner_ty, valtree)
}
_ => {
// Need to create a place for this valtree.
create_pointee_place(&mut ecx, ty, valtree)
ty::Ref(_, inner_ty, _) => {
let mut ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, CanAccessStatics::No);
let imm = valtree_to_ref(&mut ecx, valtree, *inner_ty);
let imm = ImmTy::from_immediate(imm, tcx.layout_of(param_env_ty).unwrap());
op_to_const(&ecx, &imm.into())
}
ty::Tuple(_) | ty::Array(_, _) | ty::Adt(..) => {
let layout = tcx.layout_of(param_env_ty).unwrap();
if layout.is_zst() {
// Fast path to avoid some allocations.
return ConstValue::ZeroSized;
}
if layout.abi.is_scalar()
&& (matches!(ty.kind(), ty::Tuple(_))
|| matches!(ty.kind(), ty::Adt(def, _) if def.is_struct()))
{
// A Scalar tuple/struct; we can avoid creating an allocation.
let branches = valtree.unwrap_branch();
// Find the non-ZST field. (There can be aligned ZST!)
for (i, &inner_valtree) in branches.iter().enumerate() {
let field = layout.field(&LayoutCx { tcx, param_env }, i);
if !field.is_zst() {
return valtree_to_const_value(tcx, param_env.and(field.ty), inner_valtree);
}
}
};
debug!(?place);
bug!("could not find non-ZST field during in {layout:#?}");
}

let mut ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, CanAccessStatics::No);

// Need to create a place for this valtree.
let place = create_valtree_place(&mut ecx, layout, valtree);

valtree_into_mplace(&mut ecx, &place, valtree);
dump_place(&ecx, &place);
intern_const_alloc_recursive(&mut ecx, InternKind::Constant, &place).unwrap();

match ty.kind() {
ty::Ref(_, _, _) => {
let ref_place = place.to_ref(&tcx);
let imm =
ImmTy::from_immediate(ref_place, tcx.layout_of(param_env_ty).unwrap());

op_to_const(&ecx, &imm.into())
}
_ => op_to_const(&ecx, &place.into()),
}
op_to_const(&ecx, &place.into())
}
ty::Never
| ty::Error(_)
Expand All @@ -283,6 +288,22 @@ pub fn valtree_to_const_value<'tcx>(
}
}

/// Put a valtree into memory and return a reference to that.
fn valtree_to_ref<'tcx>(
ecx: &mut CompileTimeEvalContext<'tcx, 'tcx>,
valtree: ty::ValTree<'tcx>,
pointee_ty: Ty<'tcx>,
) -> Immediate {
let pointee_place = create_valtree_place(ecx, ecx.layout_of(pointee_ty).unwrap(), valtree);
debug!(?pointee_place);

valtree_into_mplace(ecx, &pointee_place, valtree);
dump_place(ecx, &pointee_place);
intern_const_alloc_recursive(ecx, InternKind::Constant, &pointee_place).unwrap();

pointee_place.to_ref(&ecx.tcx)
}

#[instrument(skip(ecx), level = "debug")]
fn valtree_into_mplace<'tcx>(
ecx: &mut CompileTimeEvalContext<'tcx, 'tcx>,
Expand All @@ -292,7 +313,6 @@ fn valtree_into_mplace<'tcx>(
// This will match on valtree and write the value(s) corresponding to the ValTree
// inside the place recursively.

let tcx = ecx.tcx.tcx;
let ty = place.layout.ty;

match ty.kind() {
Expand All @@ -305,27 +325,8 @@ fn valtree_into_mplace<'tcx>(
ecx.write_immediate(Immediate::Scalar(scalar_int.into()), place).unwrap();
}
ty::Ref(_, inner_ty, _) => {
let pointee_place = create_pointee_place(ecx, *inner_ty, valtree);
debug!(?pointee_place);

valtree_into_mplace(ecx, &pointee_place, valtree);
dump_place(ecx, &pointee_place);
intern_const_alloc_recursive(ecx, InternKind::Constant, &pointee_place).unwrap();

let imm = match inner_ty.kind() {
ty::Slice(_) | ty::Str => {
let len = valtree.unwrap_branch().len();
let len_scalar = Scalar::from_target_usize(len as u64, &tcx);

Immediate::ScalarPair(
Scalar::from_maybe_pointer(pointee_place.ptr(), &tcx),
len_scalar,
)
}
_ => pointee_place.to_ref(&tcx),
};
let imm = valtree_to_ref(ecx, valtree, *inner_ty);
debug!(?imm);

ecx.write_immediate(imm, place).unwrap();
}
ty::Adt(_, _) | ty::Tuple(_) | ty::Array(_, _) | ty::Str | ty::Slice(_) => {
Expand Down
34 changes: 17 additions & 17 deletions compiler/rustc_middle/src/mir/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2297,7 +2297,11 @@ pub struct Constant<'tcx> {
#[derive(Clone, Copy, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable, Debug)]
#[derive(Lift, TypeFoldable, TypeVisitable)]
pub enum ConstantKind<'tcx> {
/// This constant came from the type system
/// 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.
Expand Down Expand Up @@ -2373,23 +2377,19 @@ impl<'tcx> ConstantKind<'tcx> {
param_env: ty::ParamEnv<'tcx>,
span: Option<Span>,
) -> Result<interpret::ConstValue<'tcx>, ErrorHandled> {
let (uneval, param_env) = match self {
match self {
ConstantKind::Ty(c) => {
if let ty::ConstKind::Unevaluated(uneval) = c.kind() {
// Avoid the round-trip via valtree, evaluate directly to ConstValue.
let (param_env, uneval) = uneval.prepare_for_eval(tcx, param_env);
(uneval.expand(), param_env)
} else {
// It's already a valtree, or an error.
let val = c.eval(tcx, param_env, span)?;
return Ok(tcx.valtree_to_const_val((self.ty(), val)));
}
// 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)))
}
ConstantKind::Unevaluated(uneval, _) => (uneval, param_env),
ConstantKind::Val(val, _) => return Ok(val),
};
// FIXME: We might want to have a `try_eval`-like function on `Unevaluated`
tcx.const_eval_resolve(param_env, uneval, span)
ConstantKind::Unevaluated(uneval, _) => {
// FIXME: We might want to have a `try_eval`-like function on `Unevaluated`
tcx.const_eval_resolve(param_env, uneval, span)
}
ConstantKind::Val(val, _) => Ok(val),
}
}

/// Normalizes the constant to a value or an error if possible.
Expand Down Expand Up @@ -2605,10 +2605,10 @@ impl<'tcx> ConstantKind<'tcx> {
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())
}
ty::ConstKind::Unevaluated(uv) => Self::Unevaluated(uv.expand(), c.ty()),
_ => Self::Ty(c),
}
}
Expand Down
5 changes: 0 additions & 5 deletions compiler/rustc_middle/src/ty/consts/kind.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,11 +22,6 @@ impl rustc_errors::IntoDiagnosticArg for UnevaluatedConst<'_> {
}

impl<'tcx> UnevaluatedConst<'tcx> {
#[inline]
pub fn expand(self) -> mir::UnevaluatedConst<'tcx> {
mir::UnevaluatedConst { def: self.def, args: self.args, promoted: None }
}

/// FIXME(RalfJung): I cannot explain what this does or why it makes sense, but not doing this
/// hurts performance.
#[inline]
Expand Down
42 changes: 9 additions & 33 deletions compiler/rustc_monomorphize/src/collector.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -749,39 +749,15 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
#[instrument(skip(self), level = "debug")]
fn visit_constant(&mut self, constant: &mir::Constant<'tcx>, location: Location) {
let literal = self.monomorphize(constant.literal);
let val = match literal {
mir::ConstantKind::Val(val, _) => val,
mir::ConstantKind::Ty(ct) => match ct.kind() {
ty::ConstKind::Value(val) => self.tcx.valtree_to_const_val((ct.ty(), val)),
ty::ConstKind::Unevaluated(ct) => {
debug!(?ct);
let param_env = ty::ParamEnv::reveal_all();
match self.tcx.const_eval_resolve(param_env, ct.expand(), None) {
// The `monomorphize` call should have evaluated that constant already.
Ok(val) => val,
Err(ErrorHandled::Reported(_)) => return,
Err(ErrorHandled::TooGeneric) => span_bug!(
self.body.source_info(location).span,
"collection encountered polymorphic constant: {:?}",
literal
),
}
}
_ => return,
},
mir::ConstantKind::Unevaluated(uv, _) => {
let param_env = ty::ParamEnv::reveal_all();
match self.tcx.const_eval_resolve(param_env, uv, None) {
// The `monomorphize` call should have evaluated that constant already.
Ok(val) => val,
Err(ErrorHandled::Reported(_)) => return,
Err(ErrorHandled::TooGeneric) => span_bug!(
self.body.source_info(location).span,
"collection encountered polymorphic constant: {:?}",
literal
),
}
}
let param_env = ty::ParamEnv::reveal_all();
let val = match literal.eval(self.tcx, param_env, None) {
Ok(v) => v,
Err(ErrorHandled::Reported(_)) => return,
Err(ErrorHandled::TooGeneric) => span_bug!(
self.body.source_info(location).span,
"collection encountered polymorphic constant: {:?}",
literal
),
};
collect_const_value(self.tcx, val, self.output);
MirVisitor::visit_ty(self, literal.ty(), TyContext::Location(location));
Expand Down

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