interpret: do not prune requires_caller_location stack frames quite so early
https://github.com/rust-lang/rust/pull/87000 made the interpreter skip `caller_location` frames for its stacktraces and `cur_span`. However, those functions are used for much more than just panic reporting, and e.g. when Miri reports UB somewhere, it probably wants to point inside `caller_location` frames. (And if it did not, it would want to have its own logic to decide that, not be forced into it by the core interpreter engine.) This fixes some rare ICEs in Miri that say "we should never pop more than one frame at once".
So let's remove all `caller_location` logic from the core interpreter, and instead move it to CTFE error reporting. This does not change user-visible behavior. That's the first commit.
We might additionally want to change CTFE error reporting to treat panics differently from other errors: only prune `caller_location` frames for panics. The second commit does that. But honestly I am not sure if this is an improvement.
r? ``@oli-obk``
Checking the size/alignment of an mplace may be costly, so we only do it
on the types where the walk we want to avoid could be expensive: the larger types
like arrays and slices, rather than on all aggregates being interned.
Reorganizes the previous commits to have a single exit-point to avoid doing the
potentially costly walk. Also moves the relocations tests before the interior
mutability test: only references are important when checking for `UnsafeCell`s
and we're checking if there are any to decide to avoid the walk anyways.
The interning of const allocations visits the mplace looking for references
to intern. Walking big aggregates like big static arrays can be costly,
so we only do it if the allocation we're interning contains references
or interior mutability.
Walking ZSTs was avoided before, and this optimization is now applied
to cases where there are no references/relocations either.
We now have an infallible function that also tells us which kind of allocation we are talking about.
Also we do longer have to distinguish between data and function allocations for liveness.
Remove dereferencing of Box from codegen
Through #94043, #94414, #94873, and #95328, I've been fixing issues caused by Box being treated like a pointer when it is not a pointer. However, these PRs just introduced special cases for Box. This PR removes those special cases and instead transforms a deref of Box into a deref of the pointer it contains.
Hopefully, this is the end of the Box<T, A> ICEs.
The current code is a basis for `is_const_fn_raw`, and `impl_constness`
is no longer a valid name, which is previously used for determining the
constness of impls, and not items in general.
And likewise for the `Const::val` method.
Because its type is called `ConstKind`. Also `val` is a confusing name
because `ConstKind` is an enum with seven variants, one of which is
called `Value`. Also, this gives consistency with `TyS` and `PredicateS`
which have `kind` fields.
The commit also renames a few `Const` variables from `val` to `c`, to
avoid confusion with the `ConstKind::Value` variant.
Remove unnecessary `to_string` and `String::new`
73fa217bc1 changed the type of the `suggestion` argument to `impl ToString`. This patch removes unnecessary `to_string` and `String::new`.
cc: `````@davidtwco`````
interpret: unify offset_from check with offset check
`offset` does the check with a single `check_ptr_access` call while `offset_from` used two calls. Make them both just one one call.
I originally intended to actually factor this into a common function, but I am no longer sure if that makes a lot of sense... the two functions start with pretty different precondition (e.g. `offset` *knows* that the 2nd pointer has the same provenance).
I also reworded the UB messages a little. Saying it "cannot" do something is not how we usually phrase UB (as far as I know). Instead it's not *allowed* to do that.
r? ``````@oli-obk``````
use precise spans for recursive const evaluation
This fixes https://github.com/rust-lang/rust/issues/73283 by using a `TyCtxtAt` with a more precise span when the interpreter recursively calls itself. Hopefully such calls are sufficiently rare that this does not cost us too much performance.
(In theory, cycles can also arise through layout computation, as layout can depend on consts -- but layout computation happens all the time so we'd have to do something to not make this terrible for performance.)
This commit makes type folding more like the way chalk does it.
Currently, `TypeFoldable` has `fold_with` and `super_fold_with` methods.
- `fold_with` is the standard entry point, and defaults to calling
`super_fold_with`.
- `super_fold_with` does the actual work of traversing a type.
- For a few types of interest (`Ty`, `Region`, etc.) `fold_with` instead
calls into a `TypeFolder`, which can then call back into
`super_fold_with`.
With the new approach, `TypeFoldable` has `fold_with` and
`TypeSuperFoldable` has `super_fold_with`.
- `fold_with` is still the standard entry point, *and* it does the
actual work of traversing a type, for all types except types of
interest.
- `super_fold_with` is only implemented for the types of interest.
Benefits of the new model.
- I find it easier to understand. The distinction between types of
interest and other types is clearer, and `super_fold_with` doesn't
exist for most types.
- With the current model is easy to get confused and implement a
`super_fold_with` method that should be left defaulted. (Some of the
precursor commits fixed such cases.)
- With the current model it's easy to call `super_fold_with` within
`TypeFolder` impls where `fold_with` should be called. The new
approach makes this mistake impossible, and this commit fixes a number
of such cases.
- It's potentially faster, because it avoids the `fold_with` ->
`super_fold_with` call in all cases except types of interest. A lot of
the time the compile would inline those away, but not necessarily
always.
Rollup of 5 pull requests
Successful merges:
- #97312 (Compute lifetimes in scope at diagnostic time)
- #97495 (Add E0788 for improper #[no_coverage] usage)
- #97579 (Avoid creating `SmallVec`s in `global_llvm_features`)
- #97767 (interpret: do not claim UB until we looked more into variadic functions)
- #97787 (E0432: rust 2018 -> rust 2018 or later in --explain message)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
interpret: better control over whether we read data with provenance
The resolution in https://github.com/rust-lang/unsafe-code-guidelines/issues/286 seems to be that when we load data at integer type, we implicitly strip provenance. So let's implement that in Miri at least for scalar loads. This makes use of the fact that `Scalar` layouts distinguish pointer-sized integers and pointers -- so I was expecting some wild bugs where layouts set this incorrectly, but so far that does not seem to happen.
This does not entirely implement the solution to https://github.com/rust-lang/unsafe-code-guidelines/issues/286; we still do the wrong thing for integers in larger types: we will `copy_op` them and then do validation, and validation will complain about the provenance. To fix that we need mutating validation; validation needs to strip the provenance rather than complaining about it. This is a larger undertaking (but will also help resolve https://github.com/rust-lang/miri/issues/845 since we can reset padding to `Uninit`).
The reason this is useful is that we can now implement `addr` as a `transmute` from a pointer to an integer, and actually get the desired behavior of stripping provenance without exposing it!
