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Remove DefiningAnchor::Bubble from MIR validation #116803

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Remove DefiningAnchor::Bubble from MIR validation #116803

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2661f9e
Remove DefiningAnchor::Bubble from MIR validation
compiler-errors Oct 16, 2023
7a2a791
CTFE defining anchor from current stack frame
compiler-errors Oct 16, 2023
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10 changes: 9 additions & 1 deletion compiler/rustc_const_eval/src/interpret/eval_context.rs
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Expand Up @@ -9,6 +9,7 @@ use rustc_index::IndexVec;
use rustc_middle::mir;
use rustc_middle::mir::interpret::{ErrorHandled, InvalidMetaKind, ReportedErrorInfo};
use rustc_middle::query::TyCtxtAt;
use rustc_middle::traits::DefiningAnchor;
use rustc_middle::ty::layout::{
self, FnAbiError, FnAbiOfHelpers, FnAbiRequest, LayoutError, LayoutOf, LayoutOfHelpers,
TyAndLayout,
Expand Down Expand Up @@ -384,7 +385,14 @@ pub(super) fn mir_assign_valid_types<'tcx>(
// all normal lifetimes are erased, higher-ranked types with their
// late-bound lifetimes are still around and can lead to type
// differences.
if util::relate_types(tcx, param_env, Variance::Covariant, src.ty, dest.ty) {
if util::relate_types(
tcx,
param_env,
DefiningAnchor::Error,
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CTFE is always performed with a Reveal::All param-env (or it should, as far as I'm aware?) so it makes sense to use DefiningAnchor::Error here.

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I don't think that's true? We run CTFE for const generics as well and the param-env is different there.
Cc @oli-obk @lcnr

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@compiler-errors compiler-errors Oct 16, 2023 •
edited
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My justification is wrong here. We're not using a Reveal::All param-env, but we have passed this body through the RevealAll mir-pass.

Not totally clear if that's sufficient, but if it isn't, then we don't have a test for it.

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We can also approximate the defining anchor from the current stack frame. See newest commit for approach.

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@lcnr lcnr Oct 18, 2023 •
edited
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My justification is wrong here. We're not using a Reveal::All param-env, but we have passed this body through the RevealAll mir-pass.

Not totally clear if that's sufficient, but if it isn't, then we don't have a test for it.

This is a bit of a mess. We re-use the result from running with Reveal::UserFacing when running with Reveal::All in CTFE. However, afaik there is (and well... should be) no call site actually using Reveal::UserFacing. I think we should switch to always use Reveal::All:

  • using Reveal::UserFacing after revealing opaque types can result in weird errors and failures, as we end up trying to relate an opaque and its revealed (but normally hidden) type
  • when people call a const-function returning impl Iterator<Item = u32> they actually want to be able to use the returned value as an iterator. The check that we only treat the type opaquely happened in typeck but during codegen this behavior is undesirable. I haven't thought about specialization and default associated types yet, but also, idc. cc Stop using Reveal::All before borrowck #101478 where I tried to change const generics CTFE to use Reveal::UserFacing.

Variance::Covariant,
src.ty,
dest.ty,
) {
// Make sure the layout is equal, too -- just to be safe. Miri really
// needs layout equality. For performance reason we skip this check when
// the types are equal. Equal types *can* have different layouts when
Expand Down
17 changes: 16 additions & 1 deletion compiler/rustc_const_eval/src/transform/validate.rs
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Expand Up @@ -7,6 +7,7 @@ use rustc_infer::traits::Reveal;
use rustc_middle::mir::interpret::Scalar;
use rustc_middle::mir::visit::{NonUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
use rustc_middle::traits::DefiningAnchor;
use rustc_middle::ty::{self, InstanceDef, ParamEnv, Ty, TyCtxt, TypeVisitableExt, Variance};
use rustc_mir_dataflow::impls::MaybeStorageLive;
use rustc_mir_dataflow::storage::always_storage_live_locals;
Expand Down Expand Up @@ -612,7 +613,17 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
Variance::Covariant
};

crate::util::relate_types(self.tcx, self.param_env, variance, src, dest)
crate::util::relate_types(
self.tcx,
self.param_env,
DefiningAnchor::from_def_id_and_reveal(
self.body.source.def_id(),
self.param_env.reveal(),
),
variance,
src,
dest,
)
}
}

Expand Down Expand Up @@ -767,6 +778,10 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
if !relate_types(
self.tcx,
self.param_env,
DefiningAnchor::from_def_id_and_reveal(
self.body.source.def_id(),
self.param_env.reveal(),
),
Variance::Covariant,
ty,
place_ref.ty(&self.body.local_decls, self.tcx).ty,
Expand Down
37 changes: 21 additions & 16 deletions compiler/rustc_const_eval/src/util/compare_types.rs
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Expand Up @@ -15,6 +15,7 @@ use rustc_trait_selection::traits::ObligationCtxt;
pub fn is_equal_up_to_subtyping<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
anchor: DefiningAnchor,
src: Ty<'tcx>,
dest: Ty<'tcx>,
) -> bool {
Expand All @@ -24,8 +25,8 @@ pub fn is_equal_up_to_subtyping<'tcx>(
}

// Check for subtyping in either direction.
relate_types(tcx, param_env, Variance::Covariant, src, dest)
|| relate_types(tcx, param_env, Variance::Covariant, dest, src)
relate_types(tcx, param_env, anchor, Variance::Covariant, src, dest)
|| relate_types(tcx, param_env, anchor, Variance::Covariant, dest, src)
}

/// Returns whether `src` is a subtype of `dest`, i.e. `src <: dest`.
Expand All @@ -39,6 +40,7 @@ pub fn is_equal_up_to_subtyping<'tcx>(
pub fn relate_types<'tcx>(
tcx: TyCtxt<'tcx>,
param_env: ParamEnv<'tcx>,
anchor: DefiningAnchor,
variance: Variance,
src: Ty<'tcx>,
dest: Ty<'tcx>,
Expand All @@ -47,8 +49,7 @@ pub fn relate_types<'tcx>(
return true;
}

let mut builder =
tcx.infer_ctxt().ignoring_regions().with_opaque_type_inference(DefiningAnchor::Bubble);
let mut builder = tcx.infer_ctxt().ignoring_regions().with_opaque_type_inference(anchor);
let infcx = builder.build();
let ocx = ObligationCtxt::new(&infcx);
let cause = ObligationCause::dummy();
Expand All @@ -59,19 +60,23 @@ pub fn relate_types<'tcx>(
Err(_) => return false,
};
let errors = ocx.select_all_or_error();
// With `Reveal::All`, opaque types get normalized away, with `Reveal::UserFacing`
// we would get unification errors because we're unable to look into opaque types,
// even if they're constrained in our current function.
for (key, ty) in infcx.take_opaque_types() {
let hidden_ty = tcx.type_of(key.def_id).instantiate(tcx, key.args);
if hidden_ty != ty.hidden_type.ty {
span_bug!(
ty.hidden_type.span,
"{}, {}",
tcx.type_of(key.def_id).instantiate(tcx, key.args),
ty.hidden_type.ty
);

if anchor != DefiningAnchor::Error {
// With `Reveal::All`, opaque types get normalized away, with `Reveal::UserFacing`
Comment on lines +64 to +65
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The relationship between what the if is checking (DefiningAnchor, whatever that is) and what the comment talks about (Reveal::UserFacing/Reveal::All) is completely unclear.

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Well I didn't touch that comment, but I'll rework it I guess.

// we would get unification errors because we're unable to look into opaque types,
// even if they're constrained in our current function.
for (key, ty) in infcx.take_opaque_types() {
let hidden_ty = tcx.type_of(key.def_id).instantiate(tcx, key.args);
if hidden_ty != ty.hidden_type.ty {
span_bug!(
ty.hidden_type.span,
"{}, {}",
tcx.type_of(key.def_id).instantiate(tcx, key.args),
ty.hidden_type.ty
);
}
}
}

errors.is_empty()
}
11 changes: 11 additions & 0 deletions compiler/rustc_middle/src/traits/mod.rs
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Expand Up @@ -945,3 +945,14 @@ pub enum DefiningAnchor {
/// Used to catch type mismatch errors when handling opaque types.
Error,
}

impl DefiningAnchor {
/// Mostly for use in the MIR validator, which only needs to pass a `Bind`
/// anchor if the reveal is not yet `All` and we're validating a local body.
pub fn from_def_id_and_reveal(body_def_id: DefId, reveal: Reveal) -> DefiningAnchor {
body_def_id
.as_local()
.filter(|_| reveal == Reveal::UserFacing)
.map_or(DefiningAnchor::Error, |def_id| DefiningAnchor::Bind(def_id))
}
}
4 changes: 4 additions & 0 deletions compiler/rustc_mir_transform/src/inline.rs
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Expand Up @@ -8,6 +8,7 @@ use rustc_index::Idx;
use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
use rustc_middle::mir::visit::*;
use rustc_middle::mir::*;
use rustc_middle::traits::DefiningAnchor;
use rustc_middle::ty::TypeVisitableExt;
use rustc_middle::ty::{self, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
use rustc_session::config::OptLevel;
Expand Down Expand Up @@ -221,6 +222,7 @@ impl<'tcx> Inliner<'tcx> {
if !util::relate_types(
self.tcx,
self.param_env,
DefiningAnchor::Error,
ty::Variance::Covariant,
output_type,
destination_ty,
Expand Down Expand Up @@ -257,6 +259,7 @@ impl<'tcx> Inliner<'tcx> {
if !util::relate_types(
self.tcx,
self.param_env,
DefiningAnchor::Error,
ty::Variance::Covariant,
input_type,
arg_ty,
Expand All @@ -272,6 +275,7 @@ impl<'tcx> Inliner<'tcx> {
if !util::relate_types(
self.tcx,
self.param_env,
DefiningAnchor::Error,
ty::Variance::Covariant,
input_type,
arg_ty,
Expand Down