Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Miri: avoid comparing layouts #70801

Closed
wants to merge 1 commit into from
Closed

Miri: avoid comparing layouts #70801

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
19 changes: 12 additions & 7 deletions src/librustc_mir/interpret/eval_context.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ use rustc_middle::ty::query::TyCtxtAt;
use rustc_middle::ty::subst::SubstsRef;
use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable};
use rustc_span::source_map::DUMMY_SP;
use rustc_target::abi::{Abi, Align, HasDataLayout, LayoutOf, Size, TargetDataLayout};
use rustc_target::abi::{Align, HasDataLayout, LayoutOf, Size, TargetDataLayout};

use super::{
Immediate, MPlaceTy, Machine, MemPlace, MemPlaceMeta, Memory, OpTy, Operand, Place, PlaceTy,
Expand Down Expand Up @@ -223,12 +223,17 @@ pub(super) fn mir_assign_valid_types<'tcx>(
// Type-changing assignments can happen for (at least) two reasons:
// - `&mut T` -> `&T` gets optimized from a reborrow to a mere assignment.
// - Subtyping is used. While all normal lifetimes are erased, higher-ranked lifetime
// bounds are still around and can lead to type differences.
// There is no good way to check the latter, so we compare layouts instead -- but only
// for values with `Scalar`/`ScalarPair` abi.
// FIXME: Do something more accurate, type-based.
match &src.abi {
Abi::Scalar(..) | Abi::ScalarPair(..) => src.layout == dest.layout,
// bounds on function pointers are still around and can lead to type differences.
match (&src.ty.kind, &dest.ty.kind) {
(ty::Ref(_, src_pointee, _), ty::Ref(_, dest_pointee, _)) => {
// After optimizations, there can be assignments that change reference mutability.
// This does not affect reference layout, so that is fine.
src_pointee == dest_pointee
Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I am slightly paranoid here about comparing the wrong thing (in an earlier version I accidentally compared mutabilities here instead of types, by using the wrong pattern). Is there any good way to assert that these things are types?

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

You can probably use Ty::eq to call the implementation of ==, but idk if it looks pretty.
The other option is I guess ascription, i.e. (src_pointeee: Ty) == (dest_pointee: Ty).

}
(ty::FnPtr(_), ty::FnPtr(_)) => {
// All function pointers have equal layout, and thus can be assigned.
true
}
_ => false,
}
}
Expand Down