Removing nops can allow more basic blocks to be merged, but merging
basic blocks can't allow for more nops to be removed, so we should
remove nops first.
This doesn't matter *that* much, because normally we run SimplifyCfg
several times, but there's no reason not to do it.
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.
Make the "main" constructors of NonZero/Shared/Unique return Option
Per discussion in https://github.com/rust-lang/rust/issues/27730#issuecomment-303939441.
This is a breaking change to unstable APIs.
The old behavior is still available under the name `new_unchecked`. Note that only that one can be `const fn`, since `if` is currently not allowed in constant contexts.
In the case of `NonZero` this requires adding a new `is_zero` method to the `Zeroable` trait. I mildly dislike this, but it’s not much worse than having a `Zeroable` trait in the first place. `Zeroable` and `NonZero` are both unstable, this can be reworked later.
