We lost the following comment during refactorings:
The current code for niche-filling relies on variant indices instead of actual discriminants, so enums with explicit discriminants (RFC 2363) would misbehave.
And leave only the type stuff without it.
This is because most expression stores don't have anything but types (e.g. generics, fields, signatures) so this saves a lot of memory.
This saves 58mb on `analysis-stats .`.
`rustc_pattern_analysis`: always check that deref patterns don't match on the same place as normal constructors
In rust-lang/rust#140106, deref pattern validation was tied to the `deref_patterns` feature to temporarily avoid affecting perf. However:
- As of rust-lang/rust#143414, box patterns are represented as deref patterns in `rustc_pattern_analysis`. Since they can be used by enabling `box_patterns` instead of `deref_patterns`, it was possible for them to skip validation, resulting in an ICE. This fixes that and adds a regression test.
- External tooling (e.g. rust-analyzer) will also need to validate matches containing deref patterns, which was not possible. This fixes that by making `compute_match_usefulness` validate deref patterns by default.
In order to avoid doing an extra pass for anything with patterns, the second commit makes `RustcPatCtxt` keep track of whether it encounters a deref pattern, so that it only does the check if so. This is purely for performance. If the perf impact of the first commit is negligible and the complexity cost introduced by the second commit is significant, it may be worth dropping the latter.
r? `@Nadrieril`
Allow custom default address spaces and parse `p-` specifications in the datalayout string
Some targets, such as CHERI, use as default an address space different from the "normal" default address space `0` (in the case of CHERI, [200 is used](https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-877.pdf)). Currently, `rustc` does not allow to specify custom address spaces and does not take into consideration [`p-` specifications in the datalayout string](https://llvm.org/docs/LangRef.html#langref-datalayout).
This patch tries to mitigate these problems by allowing targets to define a custom default address space (while keeping the default value to address space `0`) and adding the code to parse the `p-` specifications in `rustc_abi`. The main changes are that `TargetDataLayout` now uses functions to refer to pointer-related informations, instead of having specific fields for the size and alignment of pointers in the default address space; furthermore, the two `pointer_size` and `pointer_align` fields in `TargetDataLayout` are replaced with an `FxHashMap` that holds info for all the possible address spaces, as parsed by the `p-` specifications.
The potential performance drawbacks of not having ad-hoc fields for the default address space will be tested in this PR's CI run.
r? workingjubilee
