For box expressions, use NZ drop instead of a free block
This falls naturally out of making drop elaboration work with `box`
expressions, which is probably required for sane MIR borrow-checking.
This is a pure refactoring with no intentional functional effects.
r? @nagisa
Non-lexical lifetimes region renumberer
Regenerates region variables for all regions in a cloned MIR in the nll mir pass. This is part of the work for #43234.
This falls naturally out of making drop elaboration work with `box`
expressions, which is probably required for sane MIR borrow-checking.
This is a pure refactoring with no intentional functional effects.
Add MIR Validate statement
This adds statements to MIR that express when types are to be validated (following [Types as Contracts](https://internals.rust-lang.org/t/types-as-contracts/5562)). Obviously nothing is stabilized, and in fact a `-Z` flag has to be passed for behavior to even change at all.
This is meant to make experimentation with Types as Contracts in miri possible. The design is definitely not final.
Cc @nikomatsakis @aturon
rustc_mir: don't build unused unwind cleanup blocks
When building a scope exit, don't build unwind cleanup blocks unless they will actually be used by the unwind path of a drop - the unused blocks are removed by SimplifyCfg, but they can cause a significant performance slowdown before they are removed. That fixes#43511.
Also a few other small MIR cleanups & optimizations.
r? @eddyb
I saw MIR cache invalidation somewhat hot on my profiler when per-BB
indexin was used. That shouldn't matter much, but there is no good
reason not to use an iterator.
erase types in the move-path abstract domain
Leaving types unerased would lead to 2 types with a different "name"
getting different move-paths, which would cause major brokenness (see
e.g. #42903).
This does not fix any *known* issue, but is required if we want to use
abs_domain with non-erased regions (because the same can easily
have different names). cc @RalfJung.
r? @eddyb
Provide positional information when visiting ty, substs and closure_substs in MIR
This will enable the region renumbering portion of #43234 (non-lexical lifetimes). @nikomatsakis's current plan [here](https://gist.github.com/nikomatsakis/dfc27b28cd024eb25054b52bb11082f2) shows that we need spans of the original code to create new region variables, e.g. `self.infcx.next_region_var(infer::MiscVariable(span))`. The current visitor impls did not pass positional information (`Location` in some, `Span` and `SourceInfo` for others) for all types. I did not expand this to all visits, just the ones necessary for the above-mentioned plan.
Leaving types unerased would lead to 2 types with a different "name"
getting different move-paths, which would cause major brokenness (see
e.g. #42903).
This does not fix any *known* issue, but is required if we want to use
abs_domain with non-erased regions (because the same can easily
have different names). cc @RalfJung.
