add_retag: ensure box-to-raw-ptr casts are preserved for Miri
In https://github.com/rust-lang/rust/pull/122233 I added `retag_box_to_raw` not realizing that we can already do `addr_of_mut!(*bx)` to turn a box into a raw pointer without an intermediate reference. We just need to ensure this information is preserved past the ElaborateBoxDerefs pass.
r? ``@oli-obk``
simplify_cfg: rename some passes so that they make more sense
I was extremely confused by `SimplifyCfg::ElaborateDrops`, since it runs way later than drop elaboration. It is used e.g. in `mir-opt/retag.rs` even though that pass doesn't care about drop elaboration at all.
"Early opt" is also very confusing since that makes it sounds like it runs early during optimizations, i.e. on runtime MIR, but actually it runs way before that.
So I decided to rename
- early-opt -> post-analysis
- elaborate-drops -> pre-optimizations
I am open to other suggestions.
preserve span when evaluating mir::ConstOperand
This lets us show to the user where they were using the faulty const (which can be quite relevant when generics are involved).
I wonder if we should change "erroneous constant encountered" to something like "the above error was encountered while evaluating this constant" or so, to make this more similar to what the collector emits when showing a "backtrace" of where things get monomorphized? It seems a bit strange to rely on the order of emitted diagnostics for that but it seems the collector already [does that](da8a8c9223/compiler/rustc_monomorphize/src/collector.rs (L472-L475)).
coverage: Initial support for branch coverage instrumentation
(This is a review-ready version of the changes that were drafted in #118305.)
This PR adds support for branch coverage instrumentation, gated behind the unstable flag value `-Zcoverage-options=branch`. (Coverage instrumentation must also be enabled with `-Cinstrument-coverage`.)
During THIR-to-MIR lowering (MIR building), if branch coverage is enabled, we collect additional information about branch conditions and their corresponding then/else blocks. We inject special marker statements into those blocks, so that the `InstrumentCoverage` MIR pass can reliably identify them even after the initially-built MIR has been simplified and renumbered.
The rest of the changes are mostly just plumbing needed to gather up the information that was collected during MIR building, and include it in the coverage metadata that we embed in the final binary.
Note that `llvm-cov show` doesn't print branch coverage information in its source views by default; that needs to be explicitly enabled with `--show-branches=count` or similar.
---
The current implementation doesn't have any support for instrumenting `if let` or let-chains. I think it's still useful without that, and adding it would be non-trivial, so I'm happy to leave that for future work.
interpret: ensure that Place is never used for a different frame
We store the address where the stack frame stores its `locals`. The idea is that even if we pop and push, or switch to a different thread with a larger number of frames, then the `locals` address will most likely change so we'll notice that problem. This is made possible by some recent changes by `@WaffleLapkin,` where we no longer use `Place` across things that change the number of stack frames.
I made these debug assertions for now, just to make sure this can't cost us any perf.
The first commit is unrelated but it's a one-line comment change so it didn't warrant a separate PR...
r? `@oli-obk`
This will allow MIR building to check whether a function is eligible for
coverage instrumentation, and avoid collecting branch coverage info if it is
not.
Distinguish between library and lang UB in assert_unsafe_precondition
As described in https://github.com/rust-lang/rust/pull/121583#issuecomment-1963168186, `assert_unsafe_precondition` now explicitly distinguishes between language UB (conditions we explicitly optimize on) and library UB (things we document you shouldn't do, and maybe some library internals assume you don't do).
`debug_assert_nounwind` was originally added to avoid the "only at runtime" aspect of `assert_unsafe_precondition`. Since then the difference between the macros has gotten muddied. This totally revamps the situation.
Now _all_ preconditions shall be checked with `assert_unsafe_precondition`. If you have a precondition that's only checkable at runtime, do a `const_eval_select` hack, as done in this PR.
r? RalfJung
Add asm goto support to `asm!`
Tracking issue: #119364
This PR implements asm-goto support, using the syntax described in "future possibilities" section of [RFC2873](https://rust-lang.github.io/rfcs/2873-inline-asm.html#asm-goto).
Currently I have only implemented the `label` part, not the `fallthrough` part (i.e. fallthrough is implicit). This doesn't reduce the expressive though, since you can use label-break to get arbitrary control flow or simply set a value and rely on jump threading optimisation to get the desired control flow. I can add that later if deemed necessary.
r? ``@Amanieu``
cc ``@ojeda``
interpret: avoid a long-lived PlaceTy in stack frames
`PlaceTy` uses a representation that's not very stable under changes to the stack. I'd feel better if we didn't have one in the long-term machine state.
r? `@oli-obk`
Fix `async Fn` confirmation for `FnDef`/`FnPtr`/`Closure` types
Fixes three issues:
1. The code in `extract_tupled_inputs_and_output_from_async_callable` was accidentally getting the *future* type and the *output* type (returned by the future) messed up for fnptr/fndef/closure types. :/
2. We have a (class of) bug(s) in the old solver where we don't really support higher ranked built-in `Future` goals for generators. This is not possible to hit on stable code, but [can be hit with `unboxed_closures`](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=e935de7181e37e13515ad01720bcb899) (#121653).
* I'm opting not to fix that in this PR. Instead, I just instantiate placeholders when confirming `async Fn` goals.
4. Fixed a bug when generating `FnPtr` shims for `async Fn` trait goals.
r? oli-obk
