Fix evaluating trivial drop glue in constants
```rust
struct A;
impl Drop for A {
fn drop(&mut self) {}
}
const FOO: Option<A> = None;
const BAR: () = (FOO, ()).1;
```
was erroring with
```
error: any use of this value will cause an error
--> src/lib.rs:9:1
|
9 | const BAR: () = (FOO, ()).1;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^-^
| |
| calling non-const function `std::ptr::real_drop_in_place::<(std::option::Option<A>, ())> - shim(Some((std::option::Option<A>, ())))`
|
= note: #[deny(const_err)] on by default
error: aborting due to previous error
```
before this PR. According to godbolt this last compiled successfully in 1.27
Usually the layout of any locals is required at least three times, once
when it becomes live, once when it is written to, and once it is read
from. By adding a cache for them, we can reduce the number of layout
queries speeding up code that is heavy on const_eval.
Don't actually create a full MIR stack frame when not needed
r? @dotdash
This should significantly reduce overhead during const propagation and reduce overhead *after* copy propagation (cc https://github.com/rust-lang/rust/issues/36673)
miri engine: Stacked Borrows NG
For more refined tracking in miri, we do return untagged pointers from the memory abstraction after allocations and let the caller decide how to tag these.
Also refactor the `tag_(de)reference` hooks so they can be more easily called in the ref-to-place and place-to-ref methods, and reorder things in validation: validation calls ref-to-place which (when running in miri) triggers some checks, so we want to run it rather late and catch other problems first. We also do not need to redundantly check the ref to be allocated any more, the checks miri does anyway imply thath.
r? @oli-obk
Delayed CTFE backtraces
This renames the env var that controls CTFE backtraces from `MIRI_BACKTRACE` to `RUST_CTFE_BACKTRACE` so that we can use `MIRI_BACKTRACE` in the miri tool to only show backtraces of the main miri execution.
It also makes `RUST_CTFE_BACKTRACE` only show backtraces that actually get rendered as errors, instead of showing them eagerly when the `Err` happens. The current behavior is near useless in miri because it shows about one gazillion backtraces for errors that we later catch and do not care about. However, @oli-obk likes the current behavior for rustc CTFE work so it is still available via `RUST_CTFE_BACKTRACE=immediate`.
NOTE: This is based on top of https://github.com/rust-lang/rust/pull/53821. Only [the last three commits](https://github.com/oli-obk/rust/compare/sanity_query...RalfJung:ctfe-backtrace) are new.
Fixes https://github.com/rust-lang/rust/issues/53355
The env var is now RUST_CTFE_BACKTRACE. Similar to RUST_BACKTRACE, it usually
only prints a backtrace when the error actually surfaces, not when it happens.
This makes a difference when we catch errors.
As per @oli-obk's request, one can set RUST_CTFE_BACKTRACE=immediate to get the
backtrace shown immediately.
Report const eval error inside the query
Functional changes: We no longer warn about bad constants embedded in unused types. This relied on being able to report just a warning, not a hard error on that case, which we cannot do any more now that error reporting is consistently centralized.
r? @RalfJung
fixes#53561
