change `mir::Constant` in mir dumps
this removes duplicate information and avoids printing the `stable_crate_id` in mir dumps which broke CI in #94059
r? `@oli-obk` cc `@b-naber`
Simplify rustc_serialize by dropping support for decoding into JSON
This PR currently bundles two (somewhat separate) tasks.
First, it removes the JSON Decoder trait impl, which permitted going from JSON to Rust structs. For now, we keep supporting JSON deserialization, but only to `Json` (an equivalent of serde_json::Value). The primary hard to remove user there is for custom targets -- which need some form of JSON deserialization -- but they already have a custom ad-hoc pass for moving from Json to a Rust struct.
A [comment](e7aca89598/compiler/rustc_target/src/spec/mod.rs (L1653)) there suggests that it would be impractical to move them to a Decodable-based impl, at least without backwards compatibility concerns. I suspect that if we were widely breaking compat there, it would make sense to use serde_json at this point which would produce better error messages; the types in rustc_target are relatively isolated so we would not particularly suffer from using serde_derive.
The second part of the PR (all but the first commit) is to simplify the Decoder API by removing the non-primitive `read_*` functions. These primarily add indirection (through a closure), which doesn't directly cause a performance issue (the unique closure types essentially guarantee monomorphization), but does increase the amount of work rustc and LLVM need to do. This could be split out to a separate PR, but is included here in part to help motivate the first part.
Future work might consist of:
* Specializing enum discriminant encoding to avoid leb128 for small enums (since we know the variant count, we can directly use read/write u8 in almost all cases)
* Adding new methods to support faster deserialization (e.g., access to the underlying byte stream)
* Currently these are somewhat ad-hoc supported by specializations for e.g. `Vec<u8>`, but other types which could benefit don't today.
* Removing the Decoder trait entirely in favor of a concrete type -- today, we only really have one impl of it modulo wrappers used for specialization-based dispatch.
Highly recommend review with whitespace changes off, as the removal of closures frequently causes things to be de-indented.
Better error if the user tries to do assignment ... else
If the user tries to do assignment ... else, we now issue a more comprehensible error in the parser.
closes#93995
CTFE engine: Scalar: expose size-generic to_(u)int methods
This matches the size-generic constructors `Scalar::from_(u)int`, and it would have helped in https://github.com/rust-lang/miri/pull/1978.
r? `@oli-obk`
Use Metadata::modified instead of FileTime::from_last_modification_ti…
…me in run_cargo
Metadata::modified works in all platforms supported by the filetime
crate. This changes brings rustbuild a tiny bit closer towards dropping
the filetime dependency.
rustc_const_eval: adopt let else in more places
Continuation of #89933, #91018, #91481, #93046, #93590, #94011.
I have extended my clippy lint to also recognize tuple passing and match statements. The diff caused by fixing it is way above 1 thousand lines. Thus, I split it up into multiple pull requests to make reviewing easier. This PR handles rustc_const_eval.
Some improvements to the async docs
The goal here is to make the docs overall a little bit more comprehensive and add more links between the things.
One thing that's not working yet is the links to the keywords. Somehow I couldn't get them to work.
r? ````@GuillaumeGomez```` do you know how I could get the keyword links to work?
safely `transmute<&List<Ty<'tcx>>, &List<GenericArg<'tcx>>>`
This PR has 3 relevant steps which are is split in distinct commits.
The first commit now interns `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>` together, potentially reusing memory while allowing free conversions between these two using `List<Ty<'tcx>>::as_substs()` and `SubstsRef<'tcx>::try_as_type_list()`.
Using this, we then use `&'tcx List<Ty<'tcx>>` instead of a `SubstsRef<'tcx>` for tuple fields, simplifying a bunch of code.
Finally, as tuple fields and other generic arguments now use a different `TypeFoldable<'tcx>` impl, we optimize the impl for `List<Ty<'tcx>>` improving perf by slightly less than 1% in tuple heavy benchmarks.
Revert #93800, fixing CI time regression
This reverts commit a240ccd81c (merge commit of #93800), reversing
changes made to 393fdc1048.
This PR was likely responsible for a relatively large regression in
dist-x86_64-msvc-alt builder times, from approximately 1.7 to 2.8 hours,
bringing that builder into the pool of the slowest builders we currently have.
This seems to be limited to the alt builder due to needing parallel-compiler
enabled, likely leading to slow LLVM compilation for some reason. See some
investigation in [this Zulip stream](https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/msvc.28.3F.29.20builders.20running.20much.20slower).
cc `@lcnr` `@oli-obk` `@b-naber` (per original PRs review/author)
We can re-apply this PR once the regression is fixed, but it is sufficiently large that I don't think keeping this on master is viable in the meantime unless there's a very strong case to be made for it. Alternatively, we can disable that builder (it's not critical since it's an alt build), but that obviously carries its own costs.
Normalize obligation and expected trait_refs in confirm_poly_trait_refs
Consolidate normalization the obligation and expected trait refs in `confirm_poly_trait_refs`. Also, _always_ normalize these trait refs -- we were already normalizing the obligation trait ref when confirming closure and generator candidates, but this does it for fn pointer confirmation as well.
This presumably does more work in the case that the obligation's trait ref is already normalized, but we can see from the perf runs in #94070, it actually (paradoxically, perhaps) improves performance when paired with logic that normalizes projections in fulfillment loop.
This reverts commit a240ccd81c, reversing
changes made to 393fdc1048.
This PR was likely responsible for a relatively large regression in
dist-x86_64-msvc-alt builder times, from approximately 1.7 to 2.8 hours,
bringing that builder into the pool of the slowest builders we currently have.
This seems to be limited to the alt builder due to needing parallel-compiler
enabled, likely leading to slow LLVM compilation for some reason.
